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fix peekBitsEnding

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Andrew Kelley 2025-07-28 20:28:07 -07:00
parent 8ab91a6fe9
commit c00fb86db6
1 changed files with 21 additions and 22 deletions
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43
lib/std/compress/flate/Decompress.zig
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@ -139,11 +139,8 @@ fn dynamicCodeLength(self: *Decompress, code: u16, lens: []u4, pos: usize) !usiz
}
}
// Peek 15 bits from bits reader (maximum code len is 15 bits). Use
// decoder to find symbol for that code. We then know how many bits is
// used. Shift bit reader for that much bits, those bits are used. And
// return symbol.
fn decodeSymbol(self: *Decompress, decoder: anytype) !Symbol {
// Maximum code len is 15 bits.
const sym = try decoder.find(@bitReverse(try self.peekBits(u15)));
try self.tossBits(sym.code_bits);
return sym;
@ -451,31 +448,30 @@ fn peekBitsEnding(d: *Decompress, comptime U: type) !U {
const remaining_bits = d.remaining_bits;
const next_bits = d.next_bits;
const in = d.input;
var u: U = 0;
var u: usize = 0;
var remaining_needed_bits = @bitSizeOf(U) - remaining_bits;
var peek_len: usize = 0;
while (@bitSizeOf(U) >= 8 and remaining_needed_bits >= 8) {
peek_len += 1;
const byte = try specialPeek(in, next_bits, peek_len);
u = (u << 8) | byte;
var i: usize = 0;
while (remaining_needed_bits >= 8) {
const byte = try specialPeek(in, next_bits, i);
u |= @as(usize, byte) << @intCast(i * 8);
remaining_needed_bits -= 8;
i += 1;
}
if (remaining_needed_bits != 0) {
peek_len += 1;
const byte = try specialPeek(in, next_bits, peek_len);
u = @intCast((@as(usize, u) << remaining_needed_bits) | (byte & ((@as(usize, 1) << remaining_needed_bits) - 1)));
const byte = try specialPeek(in, next_bits, i);
u |= @as(usize, byte) << @intCast((i * 8) + remaining_needed_bits);
}
return @intCast((@as(usize, u) << remaining_bits) | next_bits);
return @truncate((u << remaining_bits) | next_bits);
}
/// If there is any unconsumed data, handles EndOfStream by pretending there
/// are zeroes afterwards.
fn specialPeek(in: *Reader, next_bits: usize, n: usize) Reader.Error!u8 {
const peeked = in.peek(n) catch |err| switch (err) {
fn specialPeek(in: *Reader, next_bits: usize, i: usize) Reader.Error!u8 {
const peeked = in.peek(i + 1) catch |err| switch (err) {
error.ReadFailed => return error.ReadFailed,
error.EndOfStream => if (next_bits == 0 and n == 0) return error.EndOfStream else return 0,
error.EndOfStream => if (next_bits == 0 and i == 0) return error.EndOfStream else return 0,
};
return peeked[n - 1];
return peeked[i];
}
fn tossBits(d: *Decompress, n: u6) !void {
@ -507,11 +503,14 @@ fn tossBitsEnding(d: *Decompress, n: u6) !void {
if (remaining_needed_bits == 0) {
d.next_bits = 0;
d.remaining_bits = 0;
} else {
const byte = try in.takeByte();
d.next_bits = @as(usize, byte) >> remaining_needed_bits;
d.remaining_bits = @intCast(8 - remaining_needed_bits);
return;
}
const byte = in.takeByte() catch |err| switch (err) {
error.ReadFailed => return error.ReadFailed,
error.EndOfStream => if (remaining_bits == 0) return error.EndOfStream else 0,
};
d.next_bits = @as(usize, byte) >> remaining_needed_bits;
d.remaining_bits = @intCast(8 - remaining_needed_bits);
}
fn takeBitsRuntime(d: *Decompress, n: u4) !u16 {