mirror of
https://codeberg.org/ziglang/zig.git
synced 2025-12-06 05:44:20 +00:00
111305678c
this is not necessary according to zig language, but works around a flaw in the C backend
1880 lines
75 KiB
Zig
1880 lines
75 KiB
Zig
const Decompress = @This();
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const std = @import("std");
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const assert = std.debug.assert;
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const Reader = std.io.Reader;
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const Limit = std.io.Limit;
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const zstd = @import("../zstd.zig");
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const Writer = std.io.Writer;
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input: *Reader,
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reader: Reader,
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state: State,
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verify_checksum: bool,
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window_len: u32,
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err: ?Error = null,
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const State = union(enum) {
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new_frame,
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in_frame: InFrame,
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skipping_frame: usize,
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end,
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const InFrame = struct {
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frame: Frame,
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checksum: ?u32,
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decompressed_size: usize,
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decode: Frame.Zstandard.Decode,
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};
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};
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pub const Options = struct {
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/// Verifying checksums is not implemented yet and will cause a panic if
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/// you set this to true.
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verify_checksum: bool = false,
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/// The output buffer is asserted to have capacity for `window_len` plus
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/// `zstd.block_size_max`.
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///
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/// If `window_len` is too small, then some streams will fail to decompress
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/// with `error.OutputBufferUndersize`.
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window_len: u32 = zstd.default_window_len,
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};
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pub const Error = error{
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BadMagic,
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BlockOversize,
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ChecksumFailure,
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ContentOversize,
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DictionaryIdFlagUnsupported,
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EndOfStream,
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HuffmanTreeIncomplete,
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InvalidBitStream,
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MalformedAccuracyLog,
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MalformedBlock,
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MalformedCompressedBlock,
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MalformedFrame,
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MalformedFseBits,
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MalformedFseTable,
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MalformedHuffmanTree,
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MalformedLiteralsHeader,
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MalformedLiteralsLength,
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MalformedLiteralsSection,
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MalformedSequence,
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MissingStartBit,
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OutputBufferUndersize,
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InputBufferUndersize,
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ReadFailed,
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RepeatModeFirst,
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ReservedBitSet,
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ReservedBlock,
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SequenceBufferUndersize,
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TreelessLiteralsFirst,
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UnexpectedEndOfLiteralStream,
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WindowOversize,
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WindowSizeUnknown,
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};
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/// When connecting `reader` to a `Writer`, `buffer` should be empty, and
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/// `Writer.buffer` capacity has requirements based on `Options.window_len`.
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///
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/// Otherwise, `buffer` has those requirements.
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pub fn init(input: *Reader, buffer: []u8, options: Options) Decompress {
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return .{
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.input = input,
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.state = .new_frame,
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.verify_checksum = options.verify_checksum,
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.window_len = options.window_len,
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.reader = .{
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.vtable = &.{
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.stream = stream,
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.rebase = rebase,
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.discard = discard,
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.readVec = readVec,
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},
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.buffer = buffer,
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.seek = 0,
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.end = 0,
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},
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};
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}
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fn rebase(r: *Reader, capacity: usize) Reader.RebaseError!void {
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const d: *Decompress = @alignCast(@fieldParentPtr("reader", r));
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assert(capacity <= r.buffer.len - d.window_len);
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assert(r.end + capacity > r.buffer.len);
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const discard_n = r.end - d.window_len;
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const keep = r.buffer[discard_n..r.end];
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@memmove(r.buffer[0..keep.len], keep);
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r.end = keep.len;
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r.seek -= discard_n;
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}
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/// This could be improved so that when an amount is discarded that includes an
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/// entire frame, skip decoding that frame.
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fn discard(r: *Reader, limit: std.Io.Limit) Reader.Error!usize {
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const d: *Decompress = @alignCast(@fieldParentPtr("reader", r));
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r.rebase(d.window_len) catch unreachable;
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var writer: Writer = .{
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.vtable = &.{
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.drain = std.Io.Writer.Discarding.drain,
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.sendFile = std.Io.Writer.Discarding.sendFile,
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},
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.buffer = r.buffer,
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.end = r.end,
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};
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const n = r.stream(&writer, limit) catch |err| switch (err) {
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error.WriteFailed => unreachable,
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error.ReadFailed => return error.ReadFailed,
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error.EndOfStream => return error.EndOfStream,
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};
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assert(n <= @intFromEnum(limit));
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return n;
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}
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fn readVec(r: *Reader, data: [][]u8) Reader.Error!usize {
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_ = data;
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const d: *Decompress = @alignCast(@fieldParentPtr("reader", r));
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assert(r.seek == r.end);
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r.rebase(d.window_len) catch unreachable;
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var writer: Writer = .{
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.buffer = r.buffer,
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.end = r.end,
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.vtable = &.{ .drain = Writer.fixedDrain },
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};
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r.end += r.vtable.stream(r, &writer, .limited(writer.buffer.len - writer.end)) catch |err| switch (err) {
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error.WriteFailed => unreachable,
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else => |e| return e,
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};
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return 0;
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}
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fn stream(r: *Reader, w: *Writer, limit: Limit) Reader.StreamError!usize {
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const d: *Decompress = @alignCast(@fieldParentPtr("reader", r));
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const in = d.input;
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switch (d.state) {
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.new_frame => {
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// Allow error.EndOfStream only on the frame magic.
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const magic = try in.takeEnumNonexhaustive(Frame.Magic, .little);
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initFrame(d, w.buffer.len, magic) catch |err| {
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d.err = err;
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return error.ReadFailed;
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};
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return readInFrame(d, w, limit, &d.state.in_frame) catch |err| switch (err) {
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error.ReadFailed => return error.ReadFailed,
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error.WriteFailed => return error.WriteFailed,
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else => |e| {
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d.err = e;
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return error.ReadFailed;
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},
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};
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},
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.in_frame => |*in_frame| {
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return readInFrame(d, w, limit, in_frame) catch |err| switch (err) {
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error.ReadFailed => return error.ReadFailed,
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error.WriteFailed => return error.WriteFailed,
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else => |e| {
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d.err = e;
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return error.ReadFailed;
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},
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};
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},
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.skipping_frame => |*remaining| {
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const n = in.discard(.limited(remaining.*)) catch |err| {
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d.err = err;
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return error.ReadFailed;
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};
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remaining.* -= n;
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if (remaining.* == 0) d.state = .new_frame;
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return 0;
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},
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.end => return error.EndOfStream,
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}
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}
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fn initFrame(d: *Decompress, window_size_max: usize, magic: Frame.Magic) !void {
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const in = d.input;
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switch (magic.kind() orelse return error.BadMagic) {
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.zstandard => {
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const header = try Frame.Zstandard.Header.decode(in);
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d.state = .{ .in_frame = .{
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.frame = try Frame.init(header, window_size_max, d.verify_checksum),
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.checksum = null,
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.decompressed_size = 0,
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.decode = .init,
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} };
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},
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.skippable => {
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const frame_size = try in.takeInt(u32, .little);
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d.state = .{ .skipping_frame = frame_size };
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},
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}
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}
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fn readInFrame(d: *Decompress, w: *Writer, limit: Limit, state: *State.InFrame) !usize {
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const in = d.input;
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const window_len = d.window_len;
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const block_header = try in.takeStruct(Frame.Zstandard.Block.Header, .little);
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const block_size = block_header.size;
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const frame_block_size_max = state.frame.block_size_max;
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if (frame_block_size_max < block_size) return error.BlockOversize;
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if (@intFromEnum(limit) < block_size) return error.OutputBufferUndersize;
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var bytes_written: usize = 0;
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switch (block_header.type) {
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.raw => {
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try in.streamExactPreserve(w, window_len, block_size);
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bytes_written = block_size;
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},
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.rle => {
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const byte = try in.takeByte();
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try w.splatBytePreserve(window_len, byte, block_size);
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bytes_written = block_size;
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},
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.compressed => {
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var literals_buffer: [zstd.block_size_max]u8 = undefined;
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var sequence_buffer: [zstd.block_size_max]u8 = undefined;
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var remaining: Limit = .limited(block_size);
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const literals = try LiteralsSection.decode(in, &remaining, &literals_buffer);
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const sequences_header = try SequencesSection.Header.decode(in, &remaining);
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const decode = &state.decode;
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try decode.prepare(in, &remaining, literals, sequences_header);
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{
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if (sequence_buffer.len < @intFromEnum(remaining))
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return error.SequenceBufferUndersize;
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const seq_slice = remaining.slice(&sequence_buffer);
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try in.readSliceAll(seq_slice);
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var bit_stream = try ReverseBitReader.init(seq_slice);
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if (sequences_header.sequence_count > 0) {
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try decode.readInitialFseState(&bit_stream);
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// Ensures the following calls to `decodeSequence` will not flush.
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if (window_len + frame_block_size_max > w.buffer.len) return error.OutputBufferUndersize;
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const dest = (try w.writableSliceGreedyPreserve(window_len, frame_block_size_max))[0..frame_block_size_max];
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const write_pos = dest.ptr - w.buffer.ptr;
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for (0..sequences_header.sequence_count - 1) |_| {
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bytes_written += try decode.decodeSequence(w.buffer, write_pos + bytes_written, &bit_stream);
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try decode.updateState(.literal, &bit_stream);
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try decode.updateState(.match, &bit_stream);
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try decode.updateState(.offset, &bit_stream);
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}
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bytes_written += try decode.decodeSequence(w.buffer, write_pos + bytes_written, &bit_stream);
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if (bytes_written > dest.len) return error.MalformedSequence;
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w.advance(bytes_written);
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}
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if (!bit_stream.isEmpty()) {
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return error.MalformedCompressedBlock;
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}
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}
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if (decode.literal_written_count < literals.header.regenerated_size) {
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const len = literals.header.regenerated_size - decode.literal_written_count;
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try decode.decodeLiterals(w, len);
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decode.literal_written_count += len;
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bytes_written += len;
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}
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switch (decode.literal_header.block_type) {
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.treeless, .compressed => {
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if (!decode.isLiteralStreamEmpty()) return error.MalformedCompressedBlock;
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},
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.raw, .rle => {},
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}
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if (bytes_written > frame_block_size_max) return error.BlockOversize;
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},
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.reserved => return error.ReservedBlock,
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}
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if (state.frame.hasher_opt) |*hasher| {
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if (bytes_written > 0) {
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_ = hasher;
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@panic("TODO all those bytes written needed to go through the hasher too");
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}
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}
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state.decompressed_size += bytes_written;
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if (block_header.last) {
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if (state.frame.has_checksum) {
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const expected_checksum = try in.takeInt(u32, .little);
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if (state.frame.hasher_opt) |*hasher| {
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const actual_checksum: u32 = @truncate(hasher.final());
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if (expected_checksum != actual_checksum) return error.ChecksumFailure;
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}
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}
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if (state.frame.content_size) |content_size| {
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if (content_size != state.decompressed_size) {
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return error.MalformedFrame;
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}
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}
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d.state = .new_frame;
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} else if (state.frame.content_size) |content_size| {
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if (state.decompressed_size > content_size) return error.MalformedFrame;
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}
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return bytes_written;
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}
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pub const Frame = struct {
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hasher_opt: ?std.hash.XxHash64,
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window_size: usize,
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has_checksum: bool,
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block_size_max: usize,
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content_size: ?usize,
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pub const Magic = enum(u32) {
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zstandard = 0xFD2FB528,
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_,
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pub fn kind(m: Magic) ?Kind {
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return switch (@intFromEnum(m)) {
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@intFromEnum(Magic.zstandard) => .zstandard,
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@intFromEnum(Skippable.magic_min)...@intFromEnum(Skippable.magic_max) => .skippable,
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else => null,
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};
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}
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pub fn isSkippable(m: Magic) bool {
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return switch (@intFromEnum(m)) {
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@intFromEnum(Skippable.magic_min)...@intFromEnum(Skippable.magic_max) => true,
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else => false,
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};
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}
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};
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pub const Kind = enum { zstandard, skippable };
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pub const Zstandard = struct {
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pub const magic: Magic = .zstandard;
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header: Header,
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data_blocks: []Block,
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checksum: ?u32,
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pub const Header = struct {
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descriptor: Descriptor,
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window_descriptor: ?u8,
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dictionary_id: ?u32,
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content_size: ?u64,
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pub const Descriptor = packed struct {
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dictionary_id_flag: u2,
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content_checksum_flag: bool,
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reserved: bool,
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unused: bool,
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single_segment_flag: bool,
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content_size_flag: u2,
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};
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pub const DecodeError = Reader.Error || error{ReservedBitSet};
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pub fn decode(in: *Reader) DecodeError!Header {
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const descriptor: Descriptor = @bitCast(try in.takeByte());
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if (descriptor.reserved) return error.ReservedBitSet;
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const window_descriptor: ?u8 = if (descriptor.single_segment_flag) null else try in.takeByte();
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const dictionary_id: ?u32 = if (descriptor.dictionary_id_flag > 0) d: {
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// if flag is 3 then field_size = 4, else field_size = flag
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const field_size = (@as(u4, 1) << descriptor.dictionary_id_flag) >> 1;
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break :d try in.takeVarInt(u32, .little, field_size);
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} else null;
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const content_size: ?u64 = if (descriptor.single_segment_flag or descriptor.content_size_flag > 0) c: {
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const field_size = @as(u4, 1) << descriptor.content_size_flag;
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const content_size = try in.takeVarInt(u64, .little, field_size);
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break :c if (field_size == 2) content_size + 256 else content_size;
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} else null;
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return .{
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.descriptor = descriptor,
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.window_descriptor = window_descriptor,
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.dictionary_id = dictionary_id,
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.content_size = content_size,
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};
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}
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/// Returns the window size required to decompress a frame, or `null` if it
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/// cannot be determined (which indicates a malformed frame header).
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pub fn windowSize(header: Header) ?u64 {
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if (header.window_descriptor) |descriptor| {
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const exponent = (descriptor & 0b11111000) >> 3;
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const mantissa = descriptor & 0b00000111;
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const window_log = 10 + exponent;
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const window_base = @as(u64, 1) << @as(u6, @intCast(window_log));
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const window_add = (window_base / 8) * mantissa;
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return window_base + window_add;
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} else return header.content_size;
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}
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};
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pub const Block = struct {
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pub const Header = packed struct(u24) {
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last: bool,
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type: Type,
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size: u21,
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};
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pub const Type = enum(u2) {
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raw,
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rle,
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compressed,
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reserved,
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};
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};
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pub const Decode = struct {
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repeat_offsets: [3]u32,
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offset: StateData(8),
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match: StateData(9),
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literal: StateData(9),
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literal_fse_buffer: [zstd.table_size_max.literal]Table.Fse,
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match_fse_buffer: [zstd.table_size_max.match]Table.Fse,
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offset_fse_buffer: [zstd.table_size_max.offset]Table.Fse,
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fse_tables_undefined: bool,
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literal_stream_reader: ReverseBitReader,
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literal_stream_index: usize,
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literal_streams: LiteralsSection.Streams,
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literal_header: LiteralsSection.Header,
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huffman_tree: ?LiteralsSection.HuffmanTree,
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literal_written_count: usize,
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fn StateData(comptime max_accuracy_log: comptime_int) type {
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return struct {
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state: @This().State,
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table: Table,
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accuracy_log: u8,
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const State = std.meta.Int(.unsigned, max_accuracy_log);
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};
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}
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const init: Decode = .{
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.repeat_offsets = .{
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zstd.start_repeated_offset_1,
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zstd.start_repeated_offset_2,
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zstd.start_repeated_offset_3,
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},
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.offset = undefined,
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.match = undefined,
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.literal = undefined,
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.literal_fse_buffer = undefined,
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.match_fse_buffer = undefined,
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.offset_fse_buffer = undefined,
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.fse_tables_undefined = true,
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.literal_written_count = 0,
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.literal_header = undefined,
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.literal_streams = undefined,
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.literal_stream_reader = undefined,
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.literal_stream_index = undefined,
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.huffman_tree = null,
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};
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|
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pub const PrepareError = error{
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/// the (reversed) literal bitstream's first byte does not have any bits set
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MissingStartBit,
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/// `literals` is a treeless literals section and the decode state does not
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|
/// have a Huffman tree from a previous block
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|
TreelessLiteralsFirst,
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/// on the first call if one of the sequence FSE tables is set to repeat mode
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|
RepeatModeFirst,
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/// an FSE table has an invalid accuracy
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MalformedAccuracyLog,
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/// failed decoding an FSE table
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MalformedFseTable,
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/// input stream ends before all FSE tables are read
|
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EndOfStream,
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ReadFailed,
|
|
InputBufferUndersize,
|
|
};
|
|
|
|
/// Prepare the decoder to decode a compressed block. Loads the
|
|
/// literals stream and Huffman tree from `literals` and reads the
|
|
/// FSE tables from `in`.
|
|
pub fn prepare(
|
|
self: *Decode,
|
|
in: *Reader,
|
|
remaining: *Limit,
|
|
literals: LiteralsSection,
|
|
sequences_header: SequencesSection.Header,
|
|
) PrepareError!void {
|
|
self.literal_written_count = 0;
|
|
self.literal_header = literals.header;
|
|
self.literal_streams = literals.streams;
|
|
|
|
if (literals.huffman_tree) |tree| {
|
|
self.huffman_tree = tree;
|
|
} else if (literals.header.block_type == .treeless and self.huffman_tree == null) {
|
|
return error.TreelessLiteralsFirst;
|
|
}
|
|
|
|
switch (literals.header.block_type) {
|
|
.raw, .rle => {},
|
|
.compressed, .treeless => {
|
|
self.literal_stream_index = 0;
|
|
switch (literals.streams) {
|
|
.one => |slice| try self.initLiteralStream(slice),
|
|
.four => |streams| try self.initLiteralStream(streams[0]),
|
|
}
|
|
},
|
|
}
|
|
|
|
if (sequences_header.sequence_count > 0) {
|
|
try self.updateFseTable(in, remaining, .literal, sequences_header.literal_lengths);
|
|
try self.updateFseTable(in, remaining, .offset, sequences_header.offsets);
|
|
try self.updateFseTable(in, remaining, .match, sequences_header.match_lengths);
|
|
self.fse_tables_undefined = false;
|
|
}
|
|
}
|
|
|
|
/// Read initial FSE states for sequence decoding.
|
|
pub fn readInitialFseState(self: *Decode, bit_reader: *ReverseBitReader) error{EndOfStream}!void {
|
|
self.literal.state = try bit_reader.readBitsNoEof(u9, self.literal.accuracy_log);
|
|
self.offset.state = try bit_reader.readBitsNoEof(u8, self.offset.accuracy_log);
|
|
self.match.state = try bit_reader.readBitsNoEof(u9, self.match.accuracy_log);
|
|
}
|
|
|
|
fn updateRepeatOffset(self: *Decode, offset: u32) void {
|
|
self.repeat_offsets[2] = self.repeat_offsets[1];
|
|
self.repeat_offsets[1] = self.repeat_offsets[0];
|
|
self.repeat_offsets[0] = offset;
|
|
}
|
|
|
|
fn useRepeatOffset(self: *Decode, index: usize) u32 {
|
|
if (index == 1)
|
|
std.mem.swap(u32, &self.repeat_offsets[0], &self.repeat_offsets[1])
|
|
else if (index == 2) {
|
|
std.mem.swap(u32, &self.repeat_offsets[0], &self.repeat_offsets[2]);
|
|
std.mem.swap(u32, &self.repeat_offsets[1], &self.repeat_offsets[2]);
|
|
}
|
|
return self.repeat_offsets[0];
|
|
}
|
|
|
|
const WhichFse = enum { offset, match, literal };
|
|
|
|
/// TODO: don't use `@field`
|
|
fn updateState(
|
|
self: *Decode,
|
|
comptime choice: WhichFse,
|
|
bit_reader: *ReverseBitReader,
|
|
) error{ MalformedFseBits, EndOfStream }!void {
|
|
switch (@field(self, @tagName(choice)).table) {
|
|
.rle => {},
|
|
.fse => |table| {
|
|
const data = table[@field(self, @tagName(choice)).state];
|
|
const T = @TypeOf(@field(self, @tagName(choice))).State;
|
|
const bits_summand = try bit_reader.readBitsNoEof(T, data.bits);
|
|
const next_state = std.math.cast(
|
|
@TypeOf(@field(self, @tagName(choice))).State,
|
|
data.baseline + bits_summand,
|
|
) orelse return error.MalformedFseBits;
|
|
@field(self, @tagName(choice)).state = next_state;
|
|
},
|
|
}
|
|
}
|
|
|
|
const FseTableError = error{
|
|
MalformedFseTable,
|
|
MalformedAccuracyLog,
|
|
RepeatModeFirst,
|
|
EndOfStream,
|
|
};
|
|
|
|
/// TODO: don't use `@field`
|
|
fn updateFseTable(
|
|
self: *Decode,
|
|
in: *Reader,
|
|
remaining: *Limit,
|
|
comptime choice: WhichFse,
|
|
mode: SequencesSection.Header.Mode,
|
|
) !void {
|
|
const field_name = @tagName(choice);
|
|
switch (mode) {
|
|
.predefined => {
|
|
@field(self, field_name).accuracy_log =
|
|
@field(zstd.default_accuracy_log, field_name);
|
|
|
|
@field(self, field_name).table =
|
|
@field(Table, "predefined_" ++ field_name);
|
|
},
|
|
.rle => {
|
|
@field(self, field_name).accuracy_log = 0;
|
|
remaining.* = remaining.subtract(1) orelse return error.EndOfStream;
|
|
@field(self, field_name).table = .{ .rle = try in.takeByte() };
|
|
},
|
|
.fse => {
|
|
const max_table_size = 2048;
|
|
const peek_len: usize = remaining.minInt(max_table_size);
|
|
if (in.buffer.len < peek_len) return error.InputBufferUndersize;
|
|
const limited_buffer = try in.peek(peek_len);
|
|
var bit_reader: BitReader = .{ .bytes = limited_buffer };
|
|
const table_size = try Table.decode(
|
|
&bit_reader,
|
|
@field(zstd.table_symbol_count_max, field_name),
|
|
@field(zstd.table_accuracy_log_max, field_name),
|
|
&@field(self, field_name ++ "_fse_buffer"),
|
|
);
|
|
@field(self, field_name).table = .{
|
|
.fse = (&@field(self, field_name ++ "_fse_buffer"))[0..table_size],
|
|
};
|
|
@field(self, field_name).accuracy_log = std.math.log2_int_ceil(usize, table_size);
|
|
in.toss(bit_reader.index);
|
|
remaining.* = remaining.subtract(bit_reader.index).?;
|
|
},
|
|
.repeat => if (self.fse_tables_undefined) return error.RepeatModeFirst,
|
|
}
|
|
}
|
|
|
|
const Sequence = struct {
|
|
literal_length: u32,
|
|
match_length: u32,
|
|
offset: u32,
|
|
};
|
|
|
|
fn nextSequence(
|
|
self: *Decode,
|
|
bit_reader: *ReverseBitReader,
|
|
) error{ InvalidBitStream, EndOfStream }!Sequence {
|
|
const raw_code = self.getCode(.offset);
|
|
const offset_code = std.math.cast(u5, raw_code) orelse {
|
|
return error.InvalidBitStream;
|
|
};
|
|
const offset_value = (@as(u32, 1) << offset_code) + try bit_reader.readBitsNoEof(u32, offset_code);
|
|
|
|
const match_code = self.getCode(.match);
|
|
if (match_code >= zstd.match_length_code_table.len)
|
|
return error.InvalidBitStream;
|
|
const match = zstd.match_length_code_table[match_code];
|
|
const match_length = match[0] + try bit_reader.readBitsNoEof(u32, match[1]);
|
|
|
|
const literal_code = self.getCode(.literal);
|
|
if (literal_code >= zstd.literals_length_code_table.len)
|
|
return error.InvalidBitStream;
|
|
const literal = zstd.literals_length_code_table[literal_code];
|
|
const literal_length = literal[0] + try bit_reader.readBitsNoEof(u32, literal[1]);
|
|
|
|
const offset = if (offset_value > 3) offset: {
|
|
const offset = offset_value - 3;
|
|
self.updateRepeatOffset(offset);
|
|
break :offset offset;
|
|
} else offset: {
|
|
if (literal_length == 0) {
|
|
if (offset_value == 3) {
|
|
const offset = self.repeat_offsets[0] - 1;
|
|
self.updateRepeatOffset(offset);
|
|
break :offset offset;
|
|
}
|
|
break :offset self.useRepeatOffset(offset_value);
|
|
}
|
|
break :offset self.useRepeatOffset(offset_value - 1);
|
|
};
|
|
|
|
if (offset == 0) return error.InvalidBitStream;
|
|
|
|
return .{
|
|
.literal_length = literal_length,
|
|
.match_length = match_length,
|
|
.offset = offset,
|
|
};
|
|
}
|
|
|
|
/// Decode one sequence from `bit_reader` into `dest`. Updates FSE states
|
|
/// if `last_sequence` is `false`. Assumes `prepare` called for the block
|
|
/// before attempting to decode sequences.
|
|
fn decodeSequence(
|
|
decode: *Decode,
|
|
dest: []u8,
|
|
write_pos: usize,
|
|
bit_reader: *ReverseBitReader,
|
|
) !usize {
|
|
const sequence = try decode.nextSequence(bit_reader);
|
|
const literal_length: usize = sequence.literal_length;
|
|
const match_length: usize = sequence.match_length;
|
|
const sequence_length = literal_length + match_length;
|
|
|
|
const copy_start = std.math.sub(usize, write_pos + sequence.literal_length, sequence.offset) catch
|
|
return error.MalformedSequence;
|
|
|
|
if (decode.literal_written_count + literal_length > decode.literal_header.regenerated_size)
|
|
return error.MalformedLiteralsLength;
|
|
var sub_bw: Writer = .fixed(dest[write_pos..]);
|
|
try decodeLiterals(decode, &sub_bw, literal_length);
|
|
decode.literal_written_count += literal_length;
|
|
// This is not a @memmove; it intentionally repeats patterns
|
|
// caused by iterating one byte at a time.
|
|
for (
|
|
dest[write_pos + literal_length ..][0..match_length],
|
|
dest[copy_start..][0..match_length],
|
|
) |*d, s| d.* = s;
|
|
return sequence_length;
|
|
}
|
|
|
|
fn nextLiteralMultiStream(self: *Decode) error{MissingStartBit}!void {
|
|
self.literal_stream_index += 1;
|
|
try self.initLiteralStream(self.literal_streams.four[self.literal_stream_index]);
|
|
}
|
|
|
|
fn initLiteralStream(self: *Decode, bytes: []const u8) error{MissingStartBit}!void {
|
|
self.literal_stream_reader = try ReverseBitReader.init(bytes);
|
|
}
|
|
|
|
fn isLiteralStreamEmpty(self: *Decode) bool {
|
|
switch (self.literal_streams) {
|
|
.one => return self.literal_stream_reader.isEmpty(),
|
|
.four => return self.literal_stream_index == 3 and self.literal_stream_reader.isEmpty(),
|
|
}
|
|
}
|
|
|
|
const LiteralBitsError = error{
|
|
MissingStartBit,
|
|
UnexpectedEndOfLiteralStream,
|
|
};
|
|
fn readLiteralsBits(
|
|
self: *Decode,
|
|
bit_count_to_read: u16,
|
|
) LiteralBitsError!u16 {
|
|
return self.literal_stream_reader.readBitsNoEof(u16, bit_count_to_read) catch bits: {
|
|
if (self.literal_streams == .four and self.literal_stream_index < 3) {
|
|
try self.nextLiteralMultiStream();
|
|
break :bits self.literal_stream_reader.readBitsNoEof(u16, bit_count_to_read) catch
|
|
return error.UnexpectedEndOfLiteralStream;
|
|
} else {
|
|
return error.UnexpectedEndOfLiteralStream;
|
|
}
|
|
};
|
|
}
|
|
|
|
/// Decode `len` bytes of literals into `w`.
|
|
fn decodeLiterals(d: *Decode, w: *Writer, len: usize) !void {
|
|
switch (d.literal_header.block_type) {
|
|
.raw => {
|
|
try w.writeAll(d.literal_streams.one[d.literal_written_count..][0..len]);
|
|
},
|
|
.rle => {
|
|
try w.splatByteAll(d.literal_streams.one[0], len);
|
|
},
|
|
.compressed, .treeless => {
|
|
if (len > w.buffer.len) return error.OutputBufferUndersize;
|
|
const buf = try w.writableSlice(len);
|
|
const huffman_tree = d.huffman_tree.?;
|
|
const max_bit_count = huffman_tree.max_bit_count;
|
|
const starting_bit_count = LiteralsSection.HuffmanTree.weightToBitCount(
|
|
huffman_tree.nodes[huffman_tree.symbol_count_minus_one].weight,
|
|
max_bit_count,
|
|
);
|
|
var bits_read: u4 = 0;
|
|
var huffman_tree_index: usize = huffman_tree.symbol_count_minus_one;
|
|
var bit_count_to_read: u4 = starting_bit_count;
|
|
for (buf) |*out| {
|
|
var prefix: u16 = 0;
|
|
while (true) {
|
|
const new_bits = try d.readLiteralsBits(bit_count_to_read);
|
|
prefix <<= bit_count_to_read;
|
|
prefix |= new_bits;
|
|
bits_read += bit_count_to_read;
|
|
const result = try huffman_tree.query(huffman_tree_index, prefix);
|
|
|
|
switch (result) {
|
|
.symbol => |sym| {
|
|
out.* = sym;
|
|
bit_count_to_read = starting_bit_count;
|
|
bits_read = 0;
|
|
huffman_tree_index = huffman_tree.symbol_count_minus_one;
|
|
break;
|
|
},
|
|
.index => |index| {
|
|
huffman_tree_index = index;
|
|
const bit_count = LiteralsSection.HuffmanTree.weightToBitCount(
|
|
huffman_tree.nodes[index].weight,
|
|
max_bit_count,
|
|
);
|
|
bit_count_to_read = bit_count - bits_read;
|
|
},
|
|
}
|
|
}
|
|
}
|
|
},
|
|
}
|
|
}
|
|
|
|
/// TODO: don't use `@field`
|
|
fn getCode(self: *Decode, comptime choice: WhichFse) u32 {
|
|
return switch (@field(self, @tagName(choice)).table) {
|
|
.rle => |value| value,
|
|
.fse => |table| table[@field(self, @tagName(choice)).state].symbol,
|
|
};
|
|
}
|
|
};
|
|
};
|
|
|
|
pub const Skippable = struct {
|
|
pub const magic_min: Magic = @enumFromInt(0x184D2A50);
|
|
pub const magic_max: Magic = @enumFromInt(0x184D2A5F);
|
|
|
|
pub const Header = struct {
|
|
magic_number: u32,
|
|
frame_size: u32,
|
|
};
|
|
};
|
|
|
|
const InitError = error{
|
|
/// Frame uses a dictionary.
|
|
DictionaryIdFlagUnsupported,
|
|
/// Frame does not have a valid window size.
|
|
WindowSizeUnknown,
|
|
/// Window size exceeds `window_size_max` or max `usize` value.
|
|
WindowOversize,
|
|
/// Frame header indicates a content size exceeding max `usize` value.
|
|
ContentOversize,
|
|
};
|
|
|
|
/// Validates `frame_header` and returns the associated `Frame`.
|
|
pub fn init(
|
|
frame_header: Frame.Zstandard.Header,
|
|
window_size_max: usize,
|
|
verify_checksum: bool,
|
|
) InitError!Frame {
|
|
if (frame_header.descriptor.dictionary_id_flag != 0)
|
|
return error.DictionaryIdFlagUnsupported;
|
|
|
|
const window_size_raw = frame_header.windowSize() orelse return error.WindowSizeUnknown;
|
|
const window_size = if (window_size_raw > window_size_max)
|
|
return error.WindowOversize
|
|
else
|
|
std.math.cast(usize, window_size_raw) orelse return error.WindowOversize;
|
|
|
|
const should_compute_checksum =
|
|
frame_header.descriptor.content_checksum_flag and verify_checksum;
|
|
|
|
const content_size = if (frame_header.content_size) |size|
|
|
std.math.cast(usize, size) orelse return error.ContentOversize
|
|
else
|
|
null;
|
|
|
|
return .{
|
|
.hasher_opt = if (should_compute_checksum) std.hash.XxHash64.init(0) else null,
|
|
.window_size = window_size,
|
|
.has_checksum = frame_header.descriptor.content_checksum_flag,
|
|
.block_size_max = @min(zstd.block_size_max, window_size),
|
|
.content_size = content_size,
|
|
};
|
|
}
|
|
};
|
|
|
|
pub const LiteralsSection = struct {
|
|
header: Header,
|
|
huffman_tree: ?HuffmanTree,
|
|
streams: Streams,
|
|
|
|
pub const Streams = union(enum) {
|
|
one: []const u8,
|
|
four: [4][]const u8,
|
|
|
|
fn decode(size_format: u2, stream_data: []const u8) !Streams {
|
|
if (size_format == 0) {
|
|
return .{ .one = stream_data };
|
|
}
|
|
|
|
if (stream_data.len < 6) return error.MalformedLiteralsSection;
|
|
|
|
const stream_1_length: usize = std.mem.readInt(u16, stream_data[0..2], .little);
|
|
const stream_2_length: usize = std.mem.readInt(u16, stream_data[2..4], .little);
|
|
const stream_3_length: usize = std.mem.readInt(u16, stream_data[4..6], .little);
|
|
|
|
const stream_1_start = 6;
|
|
const stream_2_start = stream_1_start + stream_1_length;
|
|
const stream_3_start = stream_2_start + stream_2_length;
|
|
const stream_4_start = stream_3_start + stream_3_length;
|
|
|
|
if (stream_data.len < stream_4_start) return error.MalformedLiteralsSection;
|
|
|
|
return .{ .four = .{
|
|
stream_data[stream_1_start .. stream_1_start + stream_1_length],
|
|
stream_data[stream_2_start .. stream_2_start + stream_2_length],
|
|
stream_data[stream_3_start .. stream_3_start + stream_3_length],
|
|
stream_data[stream_4_start..],
|
|
} };
|
|
}
|
|
};
|
|
|
|
pub const Header = struct {
|
|
block_type: BlockType,
|
|
size_format: u2,
|
|
regenerated_size: u20,
|
|
compressed_size: ?u18,
|
|
|
|
/// Decode a literals section header.
|
|
pub fn decode(in: *Reader, remaining: *Limit) !Header {
|
|
remaining.* = remaining.subtract(1) orelse return error.EndOfStream;
|
|
const byte0 = try in.takeByte();
|
|
const block_type: BlockType = @enumFromInt(byte0 & 0b11);
|
|
const size_format: u2 = @intCast((byte0 & 0b1100) >> 2);
|
|
var regenerated_size: u20 = undefined;
|
|
var compressed_size: ?u18 = null;
|
|
switch (block_type) {
|
|
.raw, .rle => {
|
|
switch (size_format) {
|
|
0, 2 => {
|
|
regenerated_size = byte0 >> 3;
|
|
},
|
|
1 => {
|
|
remaining.* = remaining.subtract(1) orelse return error.EndOfStream;
|
|
regenerated_size = (byte0 >> 4) + (@as(u20, try in.takeByte()) << 4);
|
|
},
|
|
3 => {
|
|
remaining.* = remaining.subtract(2) orelse return error.EndOfStream;
|
|
regenerated_size = (byte0 >> 4) +
|
|
(@as(u20, try in.takeByte()) << 4) +
|
|
(@as(u20, try in.takeByte()) << 12);
|
|
},
|
|
}
|
|
},
|
|
.compressed, .treeless => {
|
|
remaining.* = remaining.subtract(2) orelse return error.EndOfStream;
|
|
const byte1 = try in.takeByte();
|
|
const byte2 = try in.takeByte();
|
|
switch (size_format) {
|
|
0, 1 => {
|
|
regenerated_size = (byte0 >> 4) + ((@as(u20, byte1) & 0b00111111) << 4);
|
|
compressed_size = ((byte1 & 0b11000000) >> 6) + (@as(u18, byte2) << 2);
|
|
},
|
|
2 => {
|
|
remaining.* = remaining.subtract(1) orelse return error.EndOfStream;
|
|
const byte3 = try in.takeByte();
|
|
regenerated_size = (byte0 >> 4) + (@as(u20, byte1) << 4) + ((@as(u20, byte2) & 0b00000011) << 12);
|
|
compressed_size = ((byte2 & 0b11111100) >> 2) + (@as(u18, byte3) << 6);
|
|
},
|
|
3 => {
|
|
remaining.* = remaining.subtract(2) orelse return error.EndOfStream;
|
|
const byte3 = try in.takeByte();
|
|
const byte4 = try in.takeByte();
|
|
regenerated_size = (byte0 >> 4) + (@as(u20, byte1) << 4) + ((@as(u20, byte2) & 0b00111111) << 12);
|
|
compressed_size = ((byte2 & 0b11000000) >> 6) + (@as(u18, byte3) << 2) + (@as(u18, byte4) << 10);
|
|
},
|
|
}
|
|
},
|
|
}
|
|
return .{
|
|
.block_type = block_type,
|
|
.size_format = size_format,
|
|
.regenerated_size = regenerated_size,
|
|
.compressed_size = compressed_size,
|
|
};
|
|
}
|
|
};
|
|
|
|
pub const BlockType = enum(u2) {
|
|
raw,
|
|
rle,
|
|
compressed,
|
|
treeless,
|
|
};
|
|
|
|
pub const HuffmanTree = struct {
|
|
max_bit_count: u4,
|
|
symbol_count_minus_one: u8,
|
|
nodes: [256]PrefixedSymbol,
|
|
|
|
pub const PrefixedSymbol = struct {
|
|
symbol: u8,
|
|
prefix: u16,
|
|
weight: u4,
|
|
};
|
|
|
|
pub const Result = union(enum) {
|
|
symbol: u8,
|
|
index: usize,
|
|
};
|
|
|
|
pub fn query(self: HuffmanTree, index: usize, prefix: u16) error{HuffmanTreeIncomplete}!Result {
|
|
var node = self.nodes[index];
|
|
const weight = node.weight;
|
|
var i: usize = index;
|
|
while (node.weight == weight) {
|
|
if (node.prefix == prefix) return .{ .symbol = node.symbol };
|
|
if (i == 0) return error.HuffmanTreeIncomplete;
|
|
i -= 1;
|
|
node = self.nodes[i];
|
|
}
|
|
return .{ .index = i };
|
|
}
|
|
|
|
pub fn weightToBitCount(weight: u4, max_bit_count: u4) u4 {
|
|
return if (weight == 0) 0 else ((max_bit_count + 1) - weight);
|
|
}
|
|
|
|
pub const DecodeError = Reader.Error || error{
|
|
MalformedHuffmanTree,
|
|
MalformedFseTable,
|
|
MalformedAccuracyLog,
|
|
EndOfStream,
|
|
MissingStartBit,
|
|
};
|
|
|
|
pub fn decode(in: *Reader, remaining: *Limit) HuffmanTree.DecodeError!HuffmanTree {
|
|
remaining.* = remaining.subtract(1) orelse return error.EndOfStream;
|
|
const header = try in.takeByte();
|
|
if (header < 128) {
|
|
return decodeFse(in, remaining, header);
|
|
} else {
|
|
return decodeDirect(in, remaining, header - 127);
|
|
}
|
|
}
|
|
|
|
fn decodeDirect(
|
|
in: *Reader,
|
|
remaining: *Limit,
|
|
encoded_symbol_count: usize,
|
|
) HuffmanTree.DecodeError!HuffmanTree {
|
|
var weights: [256]u4 = undefined;
|
|
const weights_byte_count = (encoded_symbol_count + 1) / 2;
|
|
remaining.* = remaining.subtract(weights_byte_count) orelse return error.EndOfStream;
|
|
for (0..weights_byte_count) |i| {
|
|
const byte = try in.takeByte();
|
|
weights[2 * i] = @as(u4, @intCast(byte >> 4));
|
|
weights[2 * i + 1] = @as(u4, @intCast(byte & 0xF));
|
|
}
|
|
const symbol_count = encoded_symbol_count + 1;
|
|
return build(&weights, symbol_count);
|
|
}
|
|
|
|
fn decodeFse(
|
|
in: *Reader,
|
|
remaining: *Limit,
|
|
compressed_size: usize,
|
|
) HuffmanTree.DecodeError!HuffmanTree {
|
|
var weights: [256]u4 = undefined;
|
|
remaining.* = remaining.subtract(compressed_size) orelse return error.EndOfStream;
|
|
const compressed_buffer = try in.take(compressed_size);
|
|
var bit_reader: BitReader = .{ .bytes = compressed_buffer };
|
|
var entries: [1 << 6]Table.Fse = undefined;
|
|
const table_size = try Table.decode(&bit_reader, 256, 6, &entries);
|
|
const accuracy_log = std.math.log2_int_ceil(usize, table_size);
|
|
const remaining_buffer = bit_reader.bytes[bit_reader.index..];
|
|
const symbol_count = try assignWeights(remaining_buffer, accuracy_log, &entries, &weights);
|
|
return build(&weights, symbol_count);
|
|
}
|
|
|
|
fn assignWeights(
|
|
huff_bits_buffer: []const u8,
|
|
accuracy_log: u16,
|
|
entries: *[1 << 6]Table.Fse,
|
|
weights: *[256]u4,
|
|
) !usize {
|
|
var huff_bits = try ReverseBitReader.init(huff_bits_buffer);
|
|
|
|
var i: usize = 0;
|
|
var even_state: u32 = try huff_bits.readBitsNoEof(u32, accuracy_log);
|
|
var odd_state: u32 = try huff_bits.readBitsNoEof(u32, accuracy_log);
|
|
|
|
while (i < 254) {
|
|
const even_data = entries[even_state];
|
|
var read_bits: u16 = 0;
|
|
const even_bits = huff_bits.readBits(u32, even_data.bits, &read_bits) catch unreachable;
|
|
weights[i] = std.math.cast(u4, even_data.symbol) orelse return error.MalformedHuffmanTree;
|
|
i += 1;
|
|
if (read_bits < even_data.bits) {
|
|
weights[i] = std.math.cast(u4, entries[odd_state].symbol) orelse return error.MalformedHuffmanTree;
|
|
i += 1;
|
|
break;
|
|
}
|
|
even_state = even_data.baseline + even_bits;
|
|
|
|
read_bits = 0;
|
|
const odd_data = entries[odd_state];
|
|
const odd_bits = huff_bits.readBits(u32, odd_data.bits, &read_bits) catch unreachable;
|
|
weights[i] = std.math.cast(u4, odd_data.symbol) orelse return error.MalformedHuffmanTree;
|
|
i += 1;
|
|
if (read_bits < odd_data.bits) {
|
|
if (i == 255) return error.MalformedHuffmanTree;
|
|
weights[i] = std.math.cast(u4, entries[even_state].symbol) orelse return error.MalformedHuffmanTree;
|
|
i += 1;
|
|
break;
|
|
}
|
|
odd_state = odd_data.baseline + odd_bits;
|
|
} else return error.MalformedHuffmanTree;
|
|
|
|
if (!huff_bits.isEmpty()) {
|
|
return error.MalformedHuffmanTree;
|
|
}
|
|
|
|
return i + 1; // stream contains all but the last symbol
|
|
}
|
|
|
|
fn assignSymbols(weight_sorted_prefixed_symbols: []PrefixedSymbol, weights: [256]u4) usize {
|
|
for (0..weight_sorted_prefixed_symbols.len) |i| {
|
|
weight_sorted_prefixed_symbols[i] = .{
|
|
.symbol = @as(u8, @intCast(i)),
|
|
.weight = undefined,
|
|
.prefix = undefined,
|
|
};
|
|
}
|
|
|
|
std.mem.sort(
|
|
PrefixedSymbol,
|
|
weight_sorted_prefixed_symbols,
|
|
weights,
|
|
lessThanByWeight,
|
|
);
|
|
|
|
var prefix: u16 = 0;
|
|
var prefixed_symbol_count: usize = 0;
|
|
var sorted_index: usize = 0;
|
|
const symbol_count = weight_sorted_prefixed_symbols.len;
|
|
while (sorted_index < symbol_count) {
|
|
var symbol = weight_sorted_prefixed_symbols[sorted_index].symbol;
|
|
const weight = weights[symbol];
|
|
if (weight == 0) {
|
|
sorted_index += 1;
|
|
continue;
|
|
}
|
|
|
|
while (sorted_index < symbol_count) : ({
|
|
sorted_index += 1;
|
|
prefixed_symbol_count += 1;
|
|
prefix += 1;
|
|
}) {
|
|
symbol = weight_sorted_prefixed_symbols[sorted_index].symbol;
|
|
if (weights[symbol] != weight) {
|
|
prefix = ((prefix - 1) >> (weights[symbol] - weight)) + 1;
|
|
break;
|
|
}
|
|
weight_sorted_prefixed_symbols[prefixed_symbol_count].symbol = symbol;
|
|
weight_sorted_prefixed_symbols[prefixed_symbol_count].prefix = prefix;
|
|
weight_sorted_prefixed_symbols[prefixed_symbol_count].weight = weight;
|
|
}
|
|
}
|
|
return prefixed_symbol_count;
|
|
}
|
|
|
|
fn build(weights: *[256]u4, symbol_count: usize) error{MalformedHuffmanTree}!HuffmanTree {
|
|
var weight_power_sum_big: u32 = 0;
|
|
for (weights[0 .. symbol_count - 1]) |value| {
|
|
weight_power_sum_big += (@as(u16, 1) << value) >> 1;
|
|
}
|
|
if (weight_power_sum_big >= 1 << 11) return error.MalformedHuffmanTree;
|
|
const weight_power_sum = @as(u16, @intCast(weight_power_sum_big));
|
|
|
|
// advance to next power of two (even if weight_power_sum is a power of 2)
|
|
// TODO: is it valid to have weight_power_sum == 0?
|
|
const max_number_of_bits = if (weight_power_sum == 0) 1 else std.math.log2_int(u16, weight_power_sum) + 1;
|
|
const next_power_of_two = @as(u16, 1) << max_number_of_bits;
|
|
weights[symbol_count - 1] = std.math.log2_int(u16, next_power_of_two - weight_power_sum) + 1;
|
|
|
|
var weight_sorted_prefixed_symbols: [256]PrefixedSymbol = undefined;
|
|
const prefixed_symbol_count = assignSymbols(weight_sorted_prefixed_symbols[0..symbol_count], weights.*);
|
|
const tree: HuffmanTree = .{
|
|
.max_bit_count = max_number_of_bits,
|
|
.symbol_count_minus_one = @as(u8, @intCast(prefixed_symbol_count - 1)),
|
|
.nodes = weight_sorted_prefixed_symbols,
|
|
};
|
|
return tree;
|
|
}
|
|
|
|
fn lessThanByWeight(
|
|
weights: [256]u4,
|
|
lhs: PrefixedSymbol,
|
|
rhs: PrefixedSymbol,
|
|
) bool {
|
|
// NOTE: this function relies on the use of a stable sorting algorithm,
|
|
// otherwise a special case of if (weights[lhs] == weights[rhs]) return lhs < rhs;
|
|
// should be added
|
|
return weights[lhs.symbol] < weights[rhs.symbol];
|
|
}
|
|
};
|
|
|
|
pub const StreamCount = enum { one, four };
|
|
pub fn streamCount(size_format: u2, block_type: BlockType) StreamCount {
|
|
return switch (block_type) {
|
|
.raw, .rle => .one,
|
|
.compressed, .treeless => if (size_format == 0) .one else .four,
|
|
};
|
|
}
|
|
|
|
pub const DecodeError = error{
|
|
/// Invalid header.
|
|
MalformedLiteralsHeader,
|
|
/// Decoding errors.
|
|
MalformedLiteralsSection,
|
|
/// Compressed literals have invalid accuracy.
|
|
MalformedAccuracyLog,
|
|
/// Compressed literals have invalid FSE table.
|
|
MalformedFseTable,
|
|
/// Failed decoding a Huffamn tree.
|
|
MalformedHuffmanTree,
|
|
/// Not enough bytes to complete the section.
|
|
EndOfStream,
|
|
ReadFailed,
|
|
MissingStartBit,
|
|
};
|
|
|
|
pub fn decode(in: *Reader, remaining: *Limit, buffer: []u8) DecodeError!LiteralsSection {
|
|
const header = try Header.decode(in, remaining);
|
|
switch (header.block_type) {
|
|
.raw => {
|
|
if (buffer.len < header.regenerated_size) return error.MalformedLiteralsSection;
|
|
remaining.* = remaining.subtract(header.regenerated_size) orelse return error.EndOfStream;
|
|
try in.readSliceAll(buffer[0..header.regenerated_size]);
|
|
return .{
|
|
.header = header,
|
|
.huffman_tree = null,
|
|
.streams = .{ .one = buffer },
|
|
};
|
|
},
|
|
.rle => {
|
|
remaining.* = remaining.subtract(1) orelse return error.EndOfStream;
|
|
buffer[0] = try in.takeByte();
|
|
return .{
|
|
.header = header,
|
|
.huffman_tree = null,
|
|
.streams = .{ .one = buffer[0..1] },
|
|
};
|
|
},
|
|
.compressed, .treeless => {
|
|
const before_remaining = remaining.*;
|
|
const huffman_tree = if (header.block_type == .compressed)
|
|
try HuffmanTree.decode(in, remaining)
|
|
else
|
|
null;
|
|
const huffman_tree_size = @intFromEnum(before_remaining) - @intFromEnum(remaining.*);
|
|
const total_streams_size = std.math.sub(usize, header.compressed_size.?, huffman_tree_size) catch
|
|
return error.MalformedLiteralsSection;
|
|
if (total_streams_size > buffer.len) return error.MalformedLiteralsSection;
|
|
remaining.* = remaining.subtract(total_streams_size) orelse return error.EndOfStream;
|
|
try in.readSliceAll(buffer[0..total_streams_size]);
|
|
const stream_data = buffer[0..total_streams_size];
|
|
const streams = try Streams.decode(header.size_format, stream_data);
|
|
return .{
|
|
.header = header,
|
|
.huffman_tree = huffman_tree,
|
|
.streams = streams,
|
|
};
|
|
},
|
|
}
|
|
}
|
|
};
|
|
|
|
pub const SequencesSection = struct {
|
|
header: Header,
|
|
literals_length_table: Table,
|
|
offset_table: Table,
|
|
match_length_table: Table,
|
|
|
|
pub const Header = struct {
|
|
sequence_count: u24,
|
|
match_lengths: Mode,
|
|
offsets: Mode,
|
|
literal_lengths: Mode,
|
|
|
|
pub const Mode = enum(u2) {
|
|
predefined,
|
|
rle,
|
|
fse,
|
|
repeat,
|
|
};
|
|
|
|
pub const DecodeError = error{
|
|
ReservedBitSet,
|
|
EndOfStream,
|
|
ReadFailed,
|
|
};
|
|
|
|
pub fn decode(in: *Reader, remaining: *Limit) DecodeError!Header {
|
|
var sequence_count: u24 = undefined;
|
|
|
|
remaining.* = remaining.subtract(1) orelse return error.EndOfStream;
|
|
const byte0 = try in.takeByte();
|
|
if (byte0 == 0) {
|
|
return .{
|
|
.sequence_count = 0,
|
|
.offsets = undefined,
|
|
.match_lengths = undefined,
|
|
.literal_lengths = undefined,
|
|
};
|
|
} else if (byte0 < 128) {
|
|
remaining.* = remaining.subtract(1) orelse return error.EndOfStream;
|
|
sequence_count = byte0;
|
|
} else if (byte0 < 255) {
|
|
remaining.* = remaining.subtract(2) orelse return error.EndOfStream;
|
|
sequence_count = (@as(u24, (byte0 - 128)) << 8) + try in.takeByte();
|
|
} else {
|
|
remaining.* = remaining.subtract(3) orelse return error.EndOfStream;
|
|
sequence_count = (try in.takeByte()) + (@as(u24, try in.takeByte()) << 8) + 0x7F00;
|
|
}
|
|
|
|
const compression_modes = try in.takeByte();
|
|
|
|
const matches_mode: Header.Mode = @enumFromInt((compression_modes & 0b00001100) >> 2);
|
|
const offsets_mode: Header.Mode = @enumFromInt((compression_modes & 0b00110000) >> 4);
|
|
const literal_mode: Header.Mode = @enumFromInt((compression_modes & 0b11000000) >> 6);
|
|
if (compression_modes & 0b11 != 0) return error.ReservedBitSet;
|
|
|
|
return .{
|
|
.sequence_count = sequence_count,
|
|
.offsets = offsets_mode,
|
|
.match_lengths = matches_mode,
|
|
.literal_lengths = literal_mode,
|
|
};
|
|
}
|
|
};
|
|
};
|
|
|
|
pub const Table = union(enum) {
|
|
fse: []const Fse,
|
|
rle: u8,
|
|
|
|
pub const Fse = struct {
|
|
symbol: u8,
|
|
baseline: u16,
|
|
bits: u8,
|
|
};
|
|
|
|
pub fn decode(
|
|
bit_reader: *BitReader,
|
|
expected_symbol_count: usize,
|
|
max_accuracy_log: u4,
|
|
entries: []Table.Fse,
|
|
) !usize {
|
|
const accuracy_log_biased = try bit_reader.readBitsNoEof(u4, 4);
|
|
if (accuracy_log_biased > max_accuracy_log -| 5) return error.MalformedAccuracyLog;
|
|
const accuracy_log = accuracy_log_biased + 5;
|
|
|
|
var values: [256]u16 = undefined;
|
|
var value_count: usize = 0;
|
|
|
|
const total_probability = @as(u16, 1) << accuracy_log;
|
|
var accumulated_probability: u16 = 0;
|
|
|
|
while (accumulated_probability < total_probability) {
|
|
// WARNING: The RFC is poorly worded, and would suggest std.math.log2_int_ceil is correct here,
|
|
// but power of two (remaining probabilities + 1) need max bits set to 1 more.
|
|
const max_bits = std.math.log2_int(u16, total_probability - accumulated_probability + 1) + 1;
|
|
const small = try bit_reader.readBitsNoEof(u16, max_bits - 1);
|
|
|
|
const cutoff = (@as(u16, 1) << max_bits) - 1 - (total_probability - accumulated_probability + 1);
|
|
|
|
const value = if (small < cutoff)
|
|
small
|
|
else value: {
|
|
const value_read = small + (try bit_reader.readBitsNoEof(u16, 1) << (max_bits - 1));
|
|
break :value if (value_read < @as(u16, 1) << (max_bits - 1))
|
|
value_read
|
|
else
|
|
value_read - cutoff;
|
|
};
|
|
|
|
accumulated_probability += if (value != 0) value - 1 else 1;
|
|
|
|
values[value_count] = value;
|
|
value_count += 1;
|
|
|
|
if (value == 1) {
|
|
while (true) {
|
|
const repeat_flag = try bit_reader.readBitsNoEof(u2, 2);
|
|
if (repeat_flag + value_count > 256) return error.MalformedFseTable;
|
|
for (0..repeat_flag) |_| {
|
|
values[value_count] = 1;
|
|
value_count += 1;
|
|
}
|
|
if (repeat_flag < 3) break;
|
|
}
|
|
}
|
|
if (value_count == 256) break;
|
|
}
|
|
bit_reader.alignToByte();
|
|
|
|
if (value_count < 2) return error.MalformedFseTable;
|
|
if (accumulated_probability != total_probability) return error.MalformedFseTable;
|
|
if (value_count > expected_symbol_count) return error.MalformedFseTable;
|
|
|
|
const table_size = total_probability;
|
|
|
|
try build(values[0..value_count], entries[0..table_size]);
|
|
return table_size;
|
|
}
|
|
|
|
pub fn build(values: []const u16, entries: []Table.Fse) !void {
|
|
const total_probability = @as(u16, @intCast(entries.len));
|
|
const accuracy_log = std.math.log2_int(u16, total_probability);
|
|
assert(total_probability <= 1 << 9);
|
|
|
|
var less_than_one_count: usize = 0;
|
|
for (values, 0..) |value, i| {
|
|
if (value == 0) {
|
|
entries[entries.len - 1 - less_than_one_count] = Table.Fse{
|
|
.symbol = @as(u8, @intCast(i)),
|
|
.baseline = 0,
|
|
.bits = accuracy_log,
|
|
};
|
|
less_than_one_count += 1;
|
|
}
|
|
}
|
|
|
|
var position: usize = 0;
|
|
var temp_states: [1 << 9]u16 = undefined;
|
|
for (values, 0..) |value, symbol| {
|
|
if (value == 0 or value == 1) continue;
|
|
const probability = value - 1;
|
|
|
|
const state_share_dividend = std.math.ceilPowerOfTwo(u16, probability) catch
|
|
return error.MalformedFseTable;
|
|
const share_size = @divExact(total_probability, state_share_dividend);
|
|
const double_state_count = state_share_dividend - probability;
|
|
const single_state_count = probability - double_state_count;
|
|
const share_size_log = std.math.log2_int(u16, share_size);
|
|
|
|
for (0..probability) |i| {
|
|
temp_states[i] = @as(u16, @intCast(position));
|
|
position += (entries.len >> 1) + (entries.len >> 3) + 3;
|
|
position &= entries.len - 1;
|
|
while (position >= entries.len - less_than_one_count) {
|
|
position += (entries.len >> 1) + (entries.len >> 3) + 3;
|
|
position &= entries.len - 1;
|
|
}
|
|
}
|
|
std.mem.sort(u16, temp_states[0..probability], {}, std.sort.asc(u16));
|
|
for (0..probability) |i| {
|
|
entries[temp_states[i]] = if (i < double_state_count) Table.Fse{
|
|
.symbol = @as(u8, @intCast(symbol)),
|
|
.bits = share_size_log + 1,
|
|
.baseline = single_state_count * share_size + @as(u16, @intCast(i)) * 2 * share_size,
|
|
} else Table.Fse{
|
|
.symbol = @as(u8, @intCast(symbol)),
|
|
.bits = share_size_log,
|
|
.baseline = (@as(u16, @intCast(i)) - double_state_count) * share_size,
|
|
};
|
|
}
|
|
}
|
|
}
|
|
|
|
test build {
|
|
const literals_length_default_values = [36]u16{
|
|
5, 4, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 2, 2, 2,
|
|
3, 3, 3, 3, 3, 3, 3, 3, 3, 4, 3, 2, 2, 2, 2, 2,
|
|
0, 0, 0, 0,
|
|
};
|
|
|
|
const match_lengths_default_values = [53]u16{
|
|
2, 5, 4, 3, 3, 3, 3, 3, 3, 2, 2, 2, 2, 2, 2, 2,
|
|
2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
|
|
2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 0, 0,
|
|
0, 0, 0, 0, 0,
|
|
};
|
|
|
|
const offset_codes_default_values = [29]u16{
|
|
2, 2, 2, 2, 2, 2, 3, 3, 3, 2, 2, 2, 2, 2, 2, 2,
|
|
2, 2, 2, 2, 2, 2, 2, 2, 0, 0, 0, 0, 0,
|
|
};
|
|
|
|
var entries: [64]Table.Fse = undefined;
|
|
try build(&literals_length_default_values, &entries);
|
|
try std.testing.expectEqualSlices(Table.Fse, Table.predefined_literal.fse, &entries);
|
|
|
|
try build(&match_lengths_default_values, &entries);
|
|
try std.testing.expectEqualSlices(Table.Fse, Table.predefined_match.fse, &entries);
|
|
|
|
try build(&offset_codes_default_values, entries[0..32]);
|
|
try std.testing.expectEqualSlices(Table.Fse, Table.predefined_offset.fse, entries[0..32]);
|
|
}
|
|
|
|
pub const predefined_literal: Table = .{
|
|
.fse = &[64]Table.Fse{
|
|
.{ .symbol = 0, .bits = 4, .baseline = 0 },
|
|
.{ .symbol = 0, .bits = 4, .baseline = 16 },
|
|
.{ .symbol = 1, .bits = 5, .baseline = 32 },
|
|
.{ .symbol = 3, .bits = 5, .baseline = 0 },
|
|
.{ .symbol = 4, .bits = 5, .baseline = 0 },
|
|
.{ .symbol = 6, .bits = 5, .baseline = 0 },
|
|
.{ .symbol = 7, .bits = 5, .baseline = 0 },
|
|
.{ .symbol = 9, .bits = 5, .baseline = 0 },
|
|
.{ .symbol = 10, .bits = 5, .baseline = 0 },
|
|
.{ .symbol = 12, .bits = 5, .baseline = 0 },
|
|
.{ .symbol = 14, .bits = 6, .baseline = 0 },
|
|
.{ .symbol = 16, .bits = 5, .baseline = 0 },
|
|
.{ .symbol = 18, .bits = 5, .baseline = 0 },
|
|
.{ .symbol = 19, .bits = 5, .baseline = 0 },
|
|
.{ .symbol = 21, .bits = 5, .baseline = 0 },
|
|
.{ .symbol = 22, .bits = 5, .baseline = 0 },
|
|
.{ .symbol = 24, .bits = 5, .baseline = 0 },
|
|
.{ .symbol = 25, .bits = 5, .baseline = 32 },
|
|
.{ .symbol = 26, .bits = 5, .baseline = 0 },
|
|
.{ .symbol = 27, .bits = 6, .baseline = 0 },
|
|
.{ .symbol = 29, .bits = 6, .baseline = 0 },
|
|
.{ .symbol = 31, .bits = 6, .baseline = 0 },
|
|
.{ .symbol = 0, .bits = 4, .baseline = 32 },
|
|
.{ .symbol = 1, .bits = 4, .baseline = 0 },
|
|
.{ .symbol = 2, .bits = 5, .baseline = 0 },
|
|
.{ .symbol = 4, .bits = 5, .baseline = 32 },
|
|
.{ .symbol = 5, .bits = 5, .baseline = 0 },
|
|
.{ .symbol = 7, .bits = 5, .baseline = 32 },
|
|
.{ .symbol = 8, .bits = 5, .baseline = 0 },
|
|
.{ .symbol = 10, .bits = 5, .baseline = 32 },
|
|
.{ .symbol = 11, .bits = 5, .baseline = 0 },
|
|
.{ .symbol = 13, .bits = 6, .baseline = 0 },
|
|
.{ .symbol = 16, .bits = 5, .baseline = 32 },
|
|
.{ .symbol = 17, .bits = 5, .baseline = 0 },
|
|
.{ .symbol = 19, .bits = 5, .baseline = 32 },
|
|
.{ .symbol = 20, .bits = 5, .baseline = 0 },
|
|
.{ .symbol = 22, .bits = 5, .baseline = 32 },
|
|
.{ .symbol = 23, .bits = 5, .baseline = 0 },
|
|
.{ .symbol = 25, .bits = 4, .baseline = 0 },
|
|
.{ .symbol = 25, .bits = 4, .baseline = 16 },
|
|
.{ .symbol = 26, .bits = 5, .baseline = 32 },
|
|
.{ .symbol = 28, .bits = 6, .baseline = 0 },
|
|
.{ .symbol = 30, .bits = 6, .baseline = 0 },
|
|
.{ .symbol = 0, .bits = 4, .baseline = 48 },
|
|
.{ .symbol = 1, .bits = 4, .baseline = 16 },
|
|
.{ .symbol = 2, .bits = 5, .baseline = 32 },
|
|
.{ .symbol = 3, .bits = 5, .baseline = 32 },
|
|
.{ .symbol = 5, .bits = 5, .baseline = 32 },
|
|
.{ .symbol = 6, .bits = 5, .baseline = 32 },
|
|
.{ .symbol = 8, .bits = 5, .baseline = 32 },
|
|
.{ .symbol = 9, .bits = 5, .baseline = 32 },
|
|
.{ .symbol = 11, .bits = 5, .baseline = 32 },
|
|
.{ .symbol = 12, .bits = 5, .baseline = 32 },
|
|
.{ .symbol = 15, .bits = 6, .baseline = 0 },
|
|
.{ .symbol = 17, .bits = 5, .baseline = 32 },
|
|
.{ .symbol = 18, .bits = 5, .baseline = 32 },
|
|
.{ .symbol = 20, .bits = 5, .baseline = 32 },
|
|
.{ .symbol = 21, .bits = 5, .baseline = 32 },
|
|
.{ .symbol = 23, .bits = 5, .baseline = 32 },
|
|
.{ .symbol = 24, .bits = 5, .baseline = 32 },
|
|
.{ .symbol = 35, .bits = 6, .baseline = 0 },
|
|
.{ .symbol = 34, .bits = 6, .baseline = 0 },
|
|
.{ .symbol = 33, .bits = 6, .baseline = 0 },
|
|
.{ .symbol = 32, .bits = 6, .baseline = 0 },
|
|
},
|
|
};
|
|
|
|
pub const predefined_match: Table = .{
|
|
.fse = &[64]Table.Fse{
|
|
.{ .symbol = 0, .bits = 6, .baseline = 0 },
|
|
.{ .symbol = 1, .bits = 4, .baseline = 0 },
|
|
.{ .symbol = 2, .bits = 5, .baseline = 32 },
|
|
.{ .symbol = 3, .bits = 5, .baseline = 0 },
|
|
.{ .symbol = 5, .bits = 5, .baseline = 0 },
|
|
.{ .symbol = 6, .bits = 5, .baseline = 0 },
|
|
.{ .symbol = 8, .bits = 5, .baseline = 0 },
|
|
.{ .symbol = 10, .bits = 6, .baseline = 0 },
|
|
.{ .symbol = 13, .bits = 6, .baseline = 0 },
|
|
.{ .symbol = 16, .bits = 6, .baseline = 0 },
|
|
.{ .symbol = 19, .bits = 6, .baseline = 0 },
|
|
.{ .symbol = 22, .bits = 6, .baseline = 0 },
|
|
.{ .symbol = 25, .bits = 6, .baseline = 0 },
|
|
.{ .symbol = 28, .bits = 6, .baseline = 0 },
|
|
.{ .symbol = 31, .bits = 6, .baseline = 0 },
|
|
.{ .symbol = 33, .bits = 6, .baseline = 0 },
|
|
.{ .symbol = 35, .bits = 6, .baseline = 0 },
|
|
.{ .symbol = 37, .bits = 6, .baseline = 0 },
|
|
.{ .symbol = 39, .bits = 6, .baseline = 0 },
|
|
.{ .symbol = 41, .bits = 6, .baseline = 0 },
|
|
.{ .symbol = 43, .bits = 6, .baseline = 0 },
|
|
.{ .symbol = 45, .bits = 6, .baseline = 0 },
|
|
.{ .symbol = 1, .bits = 4, .baseline = 16 },
|
|
.{ .symbol = 2, .bits = 4, .baseline = 0 },
|
|
.{ .symbol = 3, .bits = 5, .baseline = 32 },
|
|
.{ .symbol = 4, .bits = 5, .baseline = 0 },
|
|
.{ .symbol = 6, .bits = 5, .baseline = 32 },
|
|
.{ .symbol = 7, .bits = 5, .baseline = 0 },
|
|
.{ .symbol = 9, .bits = 6, .baseline = 0 },
|
|
.{ .symbol = 12, .bits = 6, .baseline = 0 },
|
|
.{ .symbol = 15, .bits = 6, .baseline = 0 },
|
|
.{ .symbol = 18, .bits = 6, .baseline = 0 },
|
|
.{ .symbol = 21, .bits = 6, .baseline = 0 },
|
|
.{ .symbol = 24, .bits = 6, .baseline = 0 },
|
|
.{ .symbol = 27, .bits = 6, .baseline = 0 },
|
|
.{ .symbol = 30, .bits = 6, .baseline = 0 },
|
|
.{ .symbol = 32, .bits = 6, .baseline = 0 },
|
|
.{ .symbol = 34, .bits = 6, .baseline = 0 },
|
|
.{ .symbol = 36, .bits = 6, .baseline = 0 },
|
|
.{ .symbol = 38, .bits = 6, .baseline = 0 },
|
|
.{ .symbol = 40, .bits = 6, .baseline = 0 },
|
|
.{ .symbol = 42, .bits = 6, .baseline = 0 },
|
|
.{ .symbol = 44, .bits = 6, .baseline = 0 },
|
|
.{ .symbol = 1, .bits = 4, .baseline = 32 },
|
|
.{ .symbol = 1, .bits = 4, .baseline = 48 },
|
|
.{ .symbol = 2, .bits = 4, .baseline = 16 },
|
|
.{ .symbol = 4, .bits = 5, .baseline = 32 },
|
|
.{ .symbol = 5, .bits = 5, .baseline = 32 },
|
|
.{ .symbol = 7, .bits = 5, .baseline = 32 },
|
|
.{ .symbol = 8, .bits = 5, .baseline = 32 },
|
|
.{ .symbol = 11, .bits = 6, .baseline = 0 },
|
|
.{ .symbol = 14, .bits = 6, .baseline = 0 },
|
|
.{ .symbol = 17, .bits = 6, .baseline = 0 },
|
|
.{ .symbol = 20, .bits = 6, .baseline = 0 },
|
|
.{ .symbol = 23, .bits = 6, .baseline = 0 },
|
|
.{ .symbol = 26, .bits = 6, .baseline = 0 },
|
|
.{ .symbol = 29, .bits = 6, .baseline = 0 },
|
|
.{ .symbol = 52, .bits = 6, .baseline = 0 },
|
|
.{ .symbol = 51, .bits = 6, .baseline = 0 },
|
|
.{ .symbol = 50, .bits = 6, .baseline = 0 },
|
|
.{ .symbol = 49, .bits = 6, .baseline = 0 },
|
|
.{ .symbol = 48, .bits = 6, .baseline = 0 },
|
|
.{ .symbol = 47, .bits = 6, .baseline = 0 },
|
|
.{ .symbol = 46, .bits = 6, .baseline = 0 },
|
|
},
|
|
};
|
|
|
|
pub const predefined_offset: Table = .{
|
|
.fse = &[32]Table.Fse{
|
|
.{ .symbol = 0, .bits = 5, .baseline = 0 },
|
|
.{ .symbol = 6, .bits = 4, .baseline = 0 },
|
|
.{ .symbol = 9, .bits = 5, .baseline = 0 },
|
|
.{ .symbol = 15, .bits = 5, .baseline = 0 },
|
|
.{ .symbol = 21, .bits = 5, .baseline = 0 },
|
|
.{ .symbol = 3, .bits = 5, .baseline = 0 },
|
|
.{ .symbol = 7, .bits = 4, .baseline = 0 },
|
|
.{ .symbol = 12, .bits = 5, .baseline = 0 },
|
|
.{ .symbol = 18, .bits = 5, .baseline = 0 },
|
|
.{ .symbol = 23, .bits = 5, .baseline = 0 },
|
|
.{ .symbol = 5, .bits = 5, .baseline = 0 },
|
|
.{ .symbol = 8, .bits = 4, .baseline = 0 },
|
|
.{ .symbol = 14, .bits = 5, .baseline = 0 },
|
|
.{ .symbol = 20, .bits = 5, .baseline = 0 },
|
|
.{ .symbol = 2, .bits = 5, .baseline = 0 },
|
|
.{ .symbol = 7, .bits = 4, .baseline = 16 },
|
|
.{ .symbol = 11, .bits = 5, .baseline = 0 },
|
|
.{ .symbol = 17, .bits = 5, .baseline = 0 },
|
|
.{ .symbol = 22, .bits = 5, .baseline = 0 },
|
|
.{ .symbol = 4, .bits = 5, .baseline = 0 },
|
|
.{ .symbol = 8, .bits = 4, .baseline = 16 },
|
|
.{ .symbol = 13, .bits = 5, .baseline = 0 },
|
|
.{ .symbol = 19, .bits = 5, .baseline = 0 },
|
|
.{ .symbol = 1, .bits = 5, .baseline = 0 },
|
|
.{ .symbol = 6, .bits = 4, .baseline = 16 },
|
|
.{ .symbol = 10, .bits = 5, .baseline = 0 },
|
|
.{ .symbol = 16, .bits = 5, .baseline = 0 },
|
|
.{ .symbol = 28, .bits = 5, .baseline = 0 },
|
|
.{ .symbol = 27, .bits = 5, .baseline = 0 },
|
|
.{ .symbol = 26, .bits = 5, .baseline = 0 },
|
|
.{ .symbol = 25, .bits = 5, .baseline = 0 },
|
|
.{ .symbol = 24, .bits = 5, .baseline = 0 },
|
|
},
|
|
};
|
|
};
|
|
|
|
const low_bit_mask = [9]u8{
|
|
0b00000000,
|
|
0b00000001,
|
|
0b00000011,
|
|
0b00000111,
|
|
0b00001111,
|
|
0b00011111,
|
|
0b00111111,
|
|
0b01111111,
|
|
0b11111111,
|
|
};
|
|
|
|
fn Bits(comptime T: type) type {
|
|
return struct { T, u16 };
|
|
}
|
|
|
|
/// For reading the reversed bit streams used to encode FSE compressed data.
|
|
const ReverseBitReader = struct {
|
|
bytes: []const u8,
|
|
remaining: usize,
|
|
bits: u8,
|
|
count: u4,
|
|
|
|
fn init(bytes: []const u8) error{MissingStartBit}!ReverseBitReader {
|
|
var result: ReverseBitReader = .{
|
|
.bytes = bytes,
|
|
.remaining = bytes.len,
|
|
.bits = 0,
|
|
.count = 0,
|
|
};
|
|
if (bytes.len == 0) return result;
|
|
for (0..8) |_| if (0 != (result.readBitsNoEof(u1, 1) catch unreachable)) return result;
|
|
return error.MissingStartBit;
|
|
}
|
|
|
|
fn initBits(comptime T: type, out: anytype, num: u16) Bits(T) {
|
|
const UT = std.meta.Int(.unsigned, @bitSizeOf(T));
|
|
return .{
|
|
@bitCast(@as(UT, @intCast(out))),
|
|
num,
|
|
};
|
|
}
|
|
|
|
fn readBitsNoEof(self: *ReverseBitReader, comptime T: type, num: u16) error{EndOfStream}!T {
|
|
const b, const c = try self.readBitsTuple(T, num);
|
|
if (c < num) return error.EndOfStream;
|
|
return b;
|
|
}
|
|
|
|
fn readBits(self: *ReverseBitReader, comptime T: type, num: u16, out_bits: *u16) !T {
|
|
const b, const c = try self.readBitsTuple(T, num);
|
|
out_bits.* = c;
|
|
return b;
|
|
}
|
|
|
|
fn readBitsTuple(self: *ReverseBitReader, comptime T: type, num: u16) !Bits(T) {
|
|
const UT = std.meta.Int(.unsigned, @bitSizeOf(T));
|
|
const U = if (@bitSizeOf(T) < 8) u8 else UT;
|
|
|
|
if (num <= self.count) return initBits(T, self.removeBits(@intCast(num)), num);
|
|
|
|
var out_count: u16 = self.count;
|
|
var out: U = self.removeBits(self.count);
|
|
|
|
const full_bytes_left = (num - out_count) / 8;
|
|
|
|
for (0..full_bytes_left) |_| {
|
|
const byte = takeByte(self) catch |err| switch (err) {
|
|
error.EndOfStream => return initBits(T, out, out_count),
|
|
};
|
|
if (U == u8) out = 0 else out <<= 8;
|
|
out |= byte;
|
|
out_count += 8;
|
|
}
|
|
|
|
const bits_left = num - out_count;
|
|
const keep = 8 - bits_left;
|
|
|
|
if (bits_left == 0) return initBits(T, out, out_count);
|
|
|
|
const final_byte = takeByte(self) catch |err| switch (err) {
|
|
error.EndOfStream => return initBits(T, out, out_count),
|
|
};
|
|
|
|
out <<= @intCast(bits_left);
|
|
out |= final_byte >> @intCast(keep);
|
|
self.bits = final_byte & low_bit_mask[keep];
|
|
|
|
self.count = @intCast(keep);
|
|
return initBits(T, out, num);
|
|
}
|
|
|
|
fn takeByte(rbr: *ReverseBitReader) error{EndOfStream}!u8 {
|
|
if (rbr.remaining == 0) return error.EndOfStream;
|
|
rbr.remaining -= 1;
|
|
return rbr.bytes[rbr.remaining];
|
|
}
|
|
|
|
fn isEmpty(self: *const ReverseBitReader) bool {
|
|
return self.remaining == 0 and self.count == 0;
|
|
}
|
|
|
|
fn removeBits(self: *ReverseBitReader, num: u4) u8 {
|
|
if (num == 8) {
|
|
self.count = 0;
|
|
return self.bits;
|
|
}
|
|
|
|
const keep = self.count - num;
|
|
const bits = self.bits >> @intCast(keep);
|
|
self.bits &= low_bit_mask[keep];
|
|
|
|
self.count = keep;
|
|
return bits;
|
|
}
|
|
};
|
|
|
|
const BitReader = struct {
|
|
bytes: []const u8,
|
|
index: usize = 0,
|
|
bits: u8 = 0,
|
|
count: u4 = 0,
|
|
|
|
fn initBits(comptime T: type, out: anytype, num: u16) Bits(T) {
|
|
const UT = std.meta.Int(.unsigned, @bitSizeOf(T));
|
|
return .{
|
|
@bitCast(@as(UT, @intCast(out))),
|
|
num,
|
|
};
|
|
}
|
|
|
|
fn readBitsNoEof(self: *@This(), comptime T: type, num: u16) !T {
|
|
const b, const c = try self.readBitsTuple(T, num);
|
|
if (c < num) return error.EndOfStream;
|
|
return b;
|
|
}
|
|
|
|
fn readBits(self: *@This(), comptime T: type, num: u16, out_bits: *u16) !T {
|
|
const b, const c = try self.readBitsTuple(T, num);
|
|
out_bits.* = c;
|
|
return b;
|
|
}
|
|
|
|
fn readBitsTuple(self: *@This(), comptime T: type, num: u16) !Bits(T) {
|
|
const UT = std.meta.Int(.unsigned, @bitSizeOf(T));
|
|
const U = if (@bitSizeOf(T) < 8) u8 else UT;
|
|
|
|
if (num <= self.count) return initBits(T, self.removeBits(@intCast(num)), num);
|
|
|
|
var out_count: u16 = self.count;
|
|
var out: U = self.removeBits(self.count);
|
|
|
|
const full_bytes_left = (num - out_count) / 8;
|
|
|
|
for (0..full_bytes_left) |_| {
|
|
const byte = takeByte(self) catch |err| switch (err) {
|
|
error.EndOfStream => return initBits(T, out, out_count),
|
|
};
|
|
|
|
const pos = @as(U, byte) << @intCast(out_count);
|
|
out |= pos;
|
|
out_count += 8;
|
|
}
|
|
|
|
const bits_left = num - out_count;
|
|
const keep = 8 - bits_left;
|
|
|
|
if (bits_left == 0) return initBits(T, out, out_count);
|
|
|
|
const final_byte = takeByte(self) catch |err| switch (err) {
|
|
error.EndOfStream => return initBits(T, out, out_count),
|
|
};
|
|
|
|
const pos = @as(U, final_byte & low_bit_mask[bits_left]) << @intCast(out_count);
|
|
out |= pos;
|
|
self.bits = final_byte >> @intCast(bits_left);
|
|
|
|
self.count = @intCast(keep);
|
|
return initBits(T, out, num);
|
|
}
|
|
|
|
fn takeByte(br: *BitReader) error{EndOfStream}!u8 {
|
|
if (br.bytes.len - br.index == 0) return error.EndOfStream;
|
|
const result = br.bytes[br.index];
|
|
br.index += 1;
|
|
return result;
|
|
}
|
|
|
|
fn removeBits(self: *@This(), num: u4) u8 {
|
|
if (num == 8) {
|
|
self.count = 0;
|
|
return self.bits;
|
|
}
|
|
|
|
const keep = self.count - num;
|
|
const bits = self.bits & low_bit_mask[num];
|
|
self.bits >>= @intCast(num);
|
|
self.count = keep;
|
|
return bits;
|
|
}
|
|
|
|
fn alignToByte(self: *@This()) void {
|
|
self.bits = 0;
|
|
self.count = 0;
|
|
}
|
|
};
|
|
|
|
test {
|
|
_ = Table;
|
|
}
|