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Micro-optimization for decompression #320

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Merged
merged 2 commits into from
Apr 13, 2025
Merged

Micro-optimization for decompression #320

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fc2cce0
Use xor instead of sub in BitReader::refill
mat-1 Mar 22, 2025
5f18c76
add comment explaining xor optimization
mat-1 Apr 13, 2025
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4 changes: 3 additions & 1 deletion zlib-rs/src/inflate/bitreader.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -120,7 +120,9 @@ impl<'a> BitReader<'a> {
// SAFETY: assertion above ensures we have 8 bytes to read for a u64.
let read = unsafe { core::ptr::read_unaligned(self.ptr.cast::<u64>()) }.to_le();
self.bit_buffer |= read << self.bits_used;
let increment = (63 - self.bits_used) >> 3;
// this xor was previously a subtraction but was changed for performance reasons.
// for bits_used between 0 and 63 (inclusive), it will always have the same behavior.
let increment = (63 ^ self.bits_used) >> 3;
self.ptr = self.ptr.wrapping_add(increment as usize);
self.bits_used |= 56;
}
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