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more careful bit-reader interruption

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PiperOrigin-RevId: 548661043
This commit is contained in:
Evgenii Kliuchnikov 2023-07-17 05:38:37 -07:00 committed by Copybara-Service
parent c2848d5537
commit c3dc7d039c
1 changed files with 16 additions and 8 deletions
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24
c/dec/bit_reader.h
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@ -251,16 +251,23 @@ static BROTLI_INLINE void BrotliDropBits(
br->val_ >>= n_bits;
}
/* Make sure that there are no spectre bits in accumulator.
This is important for the cases when some bytes are skipped
(i.e. never placed into accumulator). */
static BROTLI_INLINE void BrotliBitReaderNormalize(BrotliBitReader* br) {
/* Actually, it is enough to normalize when br->bit_pos_ == 0 */
if (br->bit_pos_ < (sizeof(brotli_reg_t) << 3u)) {
br->val_ &= (((brotli_reg_t)1) << br->bit_pos_) - 1;
}
}
static BROTLI_INLINE void BrotliBitReaderUnload(BrotliBitReader* br) {
brotli_reg_t unused_bytes = BrotliGetAvailableBits(br) >> 3;
brotli_reg_t unused_bits = unused_bytes << 3;
br->next_in =
(unused_bytes == 0) ? br->next_in : (br->next_in - unused_bytes);
br->bit_pos_ -= unused_bits;
/* Prepare for possible input discontinuity. */
if (br->bit_pos_ == 0) {
br->val_ = 0;
}
BrotliBitReaderNormalize(br);
}
/* Reads the specified number of bits from |br| and advances the bit pos.
@ -357,10 +364,14 @@ static BROTLI_INLINE BROTLI_BOOL BrotliJumpToByteBoundary(BrotliBitReader* br) {
if (pad_bits_count != 0) {
BrotliTakeBits(br, pad_bits_count, &pad_bits);
}
BrotliBitReaderNormalize(br);
return TO_BROTLI_BOOL(pad_bits == 0);
}
static BROTLI_INLINE void BrotliDropBytes(BrotliBitReader* br, size_t num) {
/* Check detour is legal: accumulator must to be empty. */
BROTLI_DCHECK(br->bit_pos_ == 0);
BROTLI_DCHECK(br->val_ == 0);
br->next_in += num;
}
@ -375,10 +386,7 @@ static BROTLI_INLINE void BrotliCopyBytes(uint8_t* dest,
++dest;
--num;
}
/* Prepare for possible input discontinuity. */
if (br->bit_pos_ == 0) {
br->val_ = 0;
}
BrotliBitReaderNormalize(br);
if (num > 0) {
memcpy(dest, br->next_in, num);
BrotliDropBytes(br, num);