Don't check `cur_ix_masked` against `ring_buffer_mask`.

`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

4 files changed, 11 insertions, 13 deletions

diff --git a/c/enc/hash.h b/c/enc/hash.h
index ba9b0d8..f3a915b 100644
--- a/c/enc/hash.h
+++ b/c/enc/hash.h
@@ -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) {
@@ -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])) {
@@ -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;
     }
diff --git a/c/enc/hash_forgetful_chain_inc.h b/c/enc/hash_forgetful_chain_inc.h
index 9a8efeb..17f31fa 100644
--- a/c/enc/hash_forgetful_chain_inc.h
+++ b/c/enc/hash_forgetful_chain_inc.h
@@ -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;
@@ -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])) {
diff --git a/c/enc/hash_longest_match64_inc.h b/c/enc/hash_longest_match64_inc.h
index 8f825de..9834c2a 100644
--- a/c/enc/hash_longest_match64_inc.h
+++ b/c/enc/hash_longest_match64_inc.h
@@ -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;
@@ -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;
     }
@@ -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])) {
diff --git a/c/enc/hash_longest_match_inc.h b/c/enc/hash_longest_match_inc.h
index c25cdb0..42b9532 100644
--- a/c/enc/hash_longest_match_inc.h
+++ b/c/enc/hash_longest_match_inc.h
@@ -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;
@@ -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;
     }
@@ -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])) {