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more careful bit-reader interruption
PiperOrigin-RevId: 548661043
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@ -251,16 +251,23 @@ static BROTLI_INLINE void BrotliDropBits(
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br->val_ >>= n_bits;
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}
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/* Make sure that there are no spectre bits in accumulator.
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This is important for the cases when some bytes are skipped
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(i.e. never placed into accumulator). */
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static BROTLI_INLINE void BrotliBitReaderNormalize(BrotliBitReader* br) {
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/* Actually, it is enough to normalize when br->bit_pos_ == 0 */
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if (br->bit_pos_ < (sizeof(brotli_reg_t) << 3u)) {
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br->val_ &= (((brotli_reg_t)1) << br->bit_pos_) - 1;
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}
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}
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static BROTLI_INLINE void BrotliBitReaderUnload(BrotliBitReader* br) {
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brotli_reg_t unused_bytes = BrotliGetAvailableBits(br) >> 3;
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brotli_reg_t unused_bits = unused_bytes << 3;
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br->next_in =
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(unused_bytes == 0) ? br->next_in : (br->next_in - unused_bytes);
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br->bit_pos_ -= unused_bits;
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/* Prepare for possible input discontinuity. */
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if (br->bit_pos_ == 0) {
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br->val_ = 0;
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}
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BrotliBitReaderNormalize(br);
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}
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/* Reads the specified number of bits from |br| and advances the bit pos.
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@ -357,10 +364,14 @@ static BROTLI_INLINE BROTLI_BOOL BrotliJumpToByteBoundary(BrotliBitReader* br) {
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if (pad_bits_count != 0) {
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BrotliTakeBits(br, pad_bits_count, &pad_bits);
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}
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BrotliBitReaderNormalize(br);
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return TO_BROTLI_BOOL(pad_bits == 0);
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}
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static BROTLI_INLINE void BrotliDropBytes(BrotliBitReader* br, size_t num) {
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/* Check detour is legal: accumulator must to be empty. */
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BROTLI_DCHECK(br->bit_pos_ == 0);
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BROTLI_DCHECK(br->val_ == 0);
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br->next_in += num;
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}
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@ -375,10 +386,7 @@ static BROTLI_INLINE void BrotliCopyBytes(uint8_t* dest,
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++dest;
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--num;
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}
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/* Prepare for possible input discontinuity. */
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if (br->bit_pos_ == 0) {
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br->val_ = 0;
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}
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BrotliBitReaderNormalize(br);
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if (num > 0) {
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memcpy(dest, br->next_in, num);
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BrotliDropBytes(br, num);
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