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Don't check cur_ix_masked against ring_buffer_mask.
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`cur_ix_masked` isn't changing from iteration to iteration, and `max_length` ensures we never find a match long enough to walk off the ring buffer.

PiperOrigin-RevId: 624162764
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@copybara-github
Brotli authored and copybara-github committed Apr 12, 2024
1 parent a813a6a commit a76d96e
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Showing 4 changed files with 11 additions and 13 deletions.
6 changes: 3 additions & 3 deletions c/enc/hash.h
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Original file line number Diff line number Diff line change
Expand Up @@ -557,6 +557,7 @@ static BROTLI_INLINE void FindCompoundDictionaryMatch(
offset = distance_offset - distance;
limit = source_size - offset;
limit = limit > max_length ? max_length : limit;
BROTLI_DCHECK(cur_ix_masked + limit <= ring_buffer_mask)
len = FindMatchLengthWithLimit(&source[offset], &data[cur_ix_masked],
limit);
if (len >= 2) {
Expand Down Expand Up @@ -591,7 +592,7 @@ static BROTLI_INLINE void FindCompoundDictionaryMatch(
limit = source_size - offset;
limit = (limit > max_length) ? max_length : limit;
if (distance > max_distance) continue;
if (cur_ix_masked + best_len > ring_buffer_mask || best_len >= limit ||
if (best_len >= limit ||
/* compare 4 bytes ending at best_len + 1 */
BrotliUnalignedRead32(&data[cur_ix_masked + best_len - 3]) !=
BrotliUnalignedRead32(&source[offset + best_len - 3])) {
Expand Down Expand Up @@ -670,8 +671,7 @@ static BROTLI_INLINE size_t FindAllCompoundDictionaryMatches(
limit = source_size - offset;
limit = (limit > max_length) ? max_length : limit;
if (distance > max_distance) continue;
if (cur_ix_masked + best_len > ring_buffer_mask ||
best_len >= limit ||
if (best_len >= limit ||
data[cur_ix_masked + best_len] != source[offset + best_len]) {
continue;
}
Expand Down
4 changes: 2 additions & 2 deletions c/enc/hash_forgetful_chain_inc.h
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Original file line number Diff line number Diff line change
Expand Up @@ -203,6 +203,7 @@ static BROTLI_INLINE void FN(FindLongestMatch)(
uint8_t* BROTLI_RESTRICT tiny_hashes = FN(TinyHash)(self->extra[0]);
FN(Bank)* BROTLI_RESTRICT banks = FN(Banks)(self->extra[1]);
const size_t cur_ix_masked = cur_ix & ring_buffer_mask;
BROTLI_DCHECK(cur_ix_masked + max_length <= ring_buffer_mask)
/* Don't accept a short copy from far away. */
score_t min_score = out->score;
score_t best_score = out->score;
Expand Down Expand Up @@ -260,8 +261,7 @@ static BROTLI_INLINE void FN(FindLongestMatch)(
prev_ix = (cur_ix - backward) & ring_buffer_mask;
slot = banks[bank].slots[last].next;
delta = banks[bank].slots[last].delta;
if (cur_ix_masked + best_len > ring_buffer_mask ||
prev_ix + best_len > ring_buffer_mask ||
if (prev_ix + best_len > ring_buffer_mask ||
/* compare 4 bytes ending at best_len + 1 */
BrotliUnalignedRead32(&data[cur_ix_masked + best_len - 3]) !=
BrotliUnalignedRead32(&data[prev_ix + best_len - 3])) {
Expand Down
7 changes: 3 additions & 4 deletions c/enc/hash_longest_match64_inc.h
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Original file line number Diff line number Diff line change
Expand Up @@ -165,6 +165,7 @@ static BROTLI_INLINE void FN(FindLongestMatch)(
uint16_t* BROTLI_RESTRICT num = self->num_;
uint32_t* BROTLI_RESTRICT buckets = self->buckets_;
const size_t cur_ix_masked = cur_ix & ring_buffer_mask;
BROTLI_DCHECK(cur_ix_masked + max_length <= ring_buffer_mask)
/* Don't accept a short copy from far away. */
score_t min_score = out->score;
score_t best_score = out->score;
Expand All @@ -184,8 +185,7 @@ static BROTLI_INLINE void FN(FindLongestMatch)(
}
prev_ix &= ring_buffer_mask;

if (cur_ix_masked + best_len > ring_buffer_mask ||
prev_ix + best_len > ring_buffer_mask ||
if (prev_ix + best_len > ring_buffer_mask ||
data[cur_ix_masked + best_len] != data[prev_ix + best_len]) {
continue;
}
Expand Down Expand Up @@ -233,8 +233,7 @@ static BROTLI_INLINE void FN(FindLongestMatch)(
break;
}
prev_ix &= ring_buffer_mask;
if (cur_ix_masked + best_len > ring_buffer_mask ||
prev_ix + best_len > ring_buffer_mask ||
if (prev_ix + best_len > ring_buffer_mask ||
/* compare 4 bytes ending at best_len + 1 */
BrotliUnalignedRead32(&data[cur_ix_masked + best_len - 3]) !=
BrotliUnalignedRead32(&data[prev_ix + best_len - 3])) {
Expand Down
7 changes: 3 additions & 4 deletions c/enc/hash_longest_match_inc.h
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Original file line number Diff line number Diff line change
Expand Up @@ -164,6 +164,7 @@ static BROTLI_INLINE void FN(FindLongestMatch)(
uint16_t* BROTLI_RESTRICT num = self->num_;
uint32_t* BROTLI_RESTRICT buckets = self->buckets_;
const size_t cur_ix_masked = cur_ix & ring_buffer_mask;
BROTLI_DCHECK(cur_ix_masked + max_length <= ring_buffer_mask)
/* Don't accept a short copy from far away. */
score_t min_score = out->score;
score_t best_score = out->score;
Expand All @@ -183,8 +184,7 @@ static BROTLI_INLINE void FN(FindLongestMatch)(
}
prev_ix &= ring_buffer_mask;

if (cur_ix_masked + best_len > ring_buffer_mask ||
prev_ix + best_len > ring_buffer_mask ||
if (prev_ix + best_len > ring_buffer_mask ||
data[cur_ix_masked + best_len] != data[prev_ix + best_len]) {
continue;
}
Expand Down Expand Up @@ -228,8 +228,7 @@ static BROTLI_INLINE void FN(FindLongestMatch)(
break;
}
prev_ix &= ring_buffer_mask;
if (cur_ix_masked + best_len > ring_buffer_mask ||
prev_ix + best_len > ring_buffer_mask ||
if (prev_ix + best_len > ring_buffer_mask ||
/* compare 4 bytes ending at best_len + 1 */
BrotliUnalignedRead32(&data[cur_ix_masked + best_len - 3]) !=
BrotliUnalignedRead32(&data[prev_ix + best_len - 3])) {
Expand Down

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