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compress.xz: remove copyForwards from tight loop

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In the example from the issue #19052 to_read holds 213_315_584
uncompressed bytes. Calling read with small output results in many
shifts of that big buffer.
This removes need to shift to_read after each read.
This commit is contained in:
Igor Anić 2024-03-13 18:22:08 +01:00
parent b9cca3b63d
commit a21f9b6d8b
1 changed files with 10 additions and 5 deletions
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15
lib/std/compress/xz/block.zig
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@ -34,6 +34,7 @@ pub fn Decoder(comptime ReaderType: type) type {
check: xz.Check,
err: ?Error,
to_read: ArrayListUnmanaged(u8),
read_pos: usize,
block_count: usize,
fn init(allocator: Allocator, in_reader: ReaderType, check: xz.Check) !Self {
@ -43,6 +44,7 @@ pub fn Decoder(comptime ReaderType: type) type {
.check = check,
.err = null,
.to_read = .{},
.read_pos = 0,
.block_count = 0,
};
}
@ -57,13 +59,12 @@ pub fn Decoder(comptime ReaderType: type) type {
pub fn read(self: *Self, output: []u8) Error!usize {
while (true) {
if (self.to_read.items.len > 0) {
const input = self.to_read.items;
const input = self.to_read.items[self.read_pos..];
if (input.len > 0) {
const n = @min(input.len, output.len);
@memcpy(output[0..n], input[0..n]);
std.mem.copyForwards(u8, input, input[n..]);
self.to_read.shrinkRetainingCapacity(input.len - n);
if (self.to_read.items.len == 0 and self.err != null) {
self.read_pos += n;
if (self.read_pos == self.to_read.items.len and self.err != null) {
if (self.err.? == DecodeError.EndOfStreamWithNoError) {
return n;
}
@ -77,6 +78,10 @@ pub fn Decoder(comptime ReaderType: type) type {
}
return self.err.?;
}
if (self.read_pos > 0) {
self.to_read.shrinkRetainingCapacity(0);
self.read_pos = 0;
}
self.readBlock() catch |e| {
self.err = e;
};