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Fix inflate_fast_help loop bound #260

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Merged
merged 3 commits into from
Dec 10, 2024
Merged

Fix inflate_fast_help loop bound #260

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0ea8362
fix the loop bound in `inflate_fast_help`
folkertdev Dec 9, 2024
69dfcd5
make loop bound in `inflate_fast_help` slightly more accurate
folkertdev Dec 9, 2024
8ed2c63
`fn len_and_friends`: return `ControlFlow` instead of `Option`
folkertdev Dec 9, 2024
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12 changes: 7 additions & 5 deletions zlib-rs/src/inflate.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -532,7 +532,10 @@ impl State<'_> {

if avail_in >= INFLATE_FAST_MIN_HAVE && avail_out >= INFLATE_FAST_MIN_LEFT {
inflate_fast_help(self, 0);
return None;
match self.mode {
Mode::Len => {}
_ => return None,
}
}

let mut mode;
Expand Down Expand Up @@ -2027,10 +2030,9 @@ fn inflate_fast_help(state: &mut State, _start: usize) {
break 'dolen;
}

let remaining = bit_reader.bytes_remaining();
if remaining.saturating_sub(INFLATE_FAST_MIN_LEFT - 1) > 0
&& writer.remaining() > INFLATE_FAST_MIN_LEFT
{
// include the bits in the bit_reader buffer in the count of available bytes
let remaining = bit_reader.bytes_remaining_including_buffer();
if remaining >= INFLATE_FAST_MIN_HAVE && writer.remaining() >= INFLATE_FAST_MIN_LEFT {
continue;
}

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5 changes: 5 additions & 0 deletions zlib-rs/src/inflate/bitreader.rs
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Expand Up @@ -77,6 +77,11 @@ impl<'a> BitReader<'a> {
self.end as usize - self.ptr as usize
}

#[inline(always)]
pub fn bytes_remaining_including_buffer(&self) -> usize {
(self.end as usize - self.ptr as usize) + (self.bits_used as usize >> 3)
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Using / 8 instead of >> 3 may be a bit clearer and will optimize to the same assembly.

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we can make a pass over the repo at some point. I think zlib-ng never updated this, and the original zlib that it forked was written at a time when apparently that optimization was not (effectively) guaranteed.

}

#[inline(always)]
pub fn need_bits(&mut self, n: usize) -> Result<(), ReturnCode> {
while (self.bits_used as usize) < n {
Expand Down