Update brotli to v1.0.0-snapshot.

third_party/brotli/enc/backward_references_inc.h

+/* NOLINT(build/header_guard) */
+/* Copyright 2013 Google Inc. All Rights Reserved.
+
+   Distributed under MIT license.
+   See file LICENSE for detail or copy at https://opensource.org/licenses/MIT
+*/
+
+/* template parameters: FN */
+
+#define Hasher HASHER()
+
+static BROTLI_NOINLINE void FN(CreateBackwardReferences)(
+    MemoryManager* m, size_t num_bytes, size_t position, BROTLI_BOOL is_last,
+    const uint8_t* ringbuffer, size_t ringbuffer_mask,
+    const BrotliEncoderParams* params, Hasher* hasher, int* dist_cache,
+    size_t* last_insert_len, Command* commands, size_t* num_commands,
+    size_t* num_literals) {
+  /* Set maximum distance, see section 9.1. of the spec. */
+  const size_t max_backward_limit = MaxBackwardLimit(params->lgwin);
+
+  const Command* const orig_commands = commands;
+  size_t insert_length = *last_insert_len;
+  const size_t pos_end = position + num_bytes;
+  const size_t store_end = num_bytes >= FN(StoreLookahead)() ?
+      position + num_bytes - FN(StoreLookahead)() + 1 : position;
+
+  /* For speed up heuristics for random data. */
+  const size_t random_heuristics_window_size =
+      LiteralSpreeLengthForSparseSearch(params);
+  size_t apply_random_heuristics = position + random_heuristics_window_size;
+
+  /* Minimum score to accept a backward reference. */
+  const score_t kMinScore = BROTLI_SCORE_BASE + 400;
+
+  FN(Init)(m, hasher, ringbuffer, params, position, num_bytes, is_last);
+  if (BROTLI_IS_OOM(m)) return;
+  FN(StitchToPreviousBlock)(hasher, num_bytes, position,
+                            ringbuffer, ringbuffer_mask);
+
+  while (position + FN(HashTypeLength)() < pos_end) {
+    size_t max_length = pos_end - position;
+    size_t max_distance = BROTLI_MIN(size_t, position, max_backward_limit);
+    HasherSearchResult sr;
+    sr.len = 0;
+    sr.len_x_code = 0;
+    sr.distance = 0;
+    sr.score = kMinScore;
+    if (FN(FindLongestMatch)(hasher, ringbuffer, ringbuffer_mask, dist_cache,
+                             position, max_length, max_distance, &sr)) {
+      /* Found a match. Let's look for something even better ahead. */
+      int delayed_backward_references_in_row = 0;
+      --max_length;
+      for (;; --max_length) {
+        const score_t cost_diff_lazy = 700;
+        BROTLI_BOOL is_match_found;
+        HasherSearchResult sr2;
+        sr2.len = params->quality < MIN_QUALITY_FOR_EXTENSIVE_REFERENCE_SEARCH ?
+            BROTLI_MIN(size_t, sr.len - 1, max_length) : 0;
+        sr2.len_x_code = 0;
+        sr2.distance = 0;
+        sr2.score = kMinScore;
+        max_distance = BROTLI_MIN(size_t, position + 1, max_backward_limit);
+        is_match_found = FN(FindLongestMatch)(hasher, ringbuffer,
+            ringbuffer_mask, dist_cache, position + 1, max_length, max_distance,
+            &sr2);
+        if (is_match_found && sr2.score >= sr.score + cost_diff_lazy) {
+          /* Ok, let's just write one byte for now and start a match from the
+             next byte. */
+          ++position;
+          ++insert_length;
+          sr = sr2;
+          if (++delayed_backward_references_in_row < 4 &&
+              position + FN(HashTypeLength)() < pos_end) {
+            continue;
+          }
+        }
+        break;
+      }
+      apply_random_heuristics =
+          position + 2 * sr.len + random_heuristics_window_size;
+      max_distance = BROTLI_MIN(size_t, position, max_backward_limit);
+      {
+        /* The first 16 codes are special short-codes,
+           and the minimum offset is 1. */
+        size_t distance_code =
+            ComputeDistanceCode(sr.distance, max_distance, dist_cache);
+        if (sr.distance <= max_distance && distance_code > 0) {
+          dist_cache[3] = dist_cache[2];
+          dist_cache[2] = dist_cache[1];
+          dist_cache[1] = dist_cache[0];
+          dist_cache[0] = (int)sr.distance;
+        }
+        InitCommand(commands++, insert_length, sr.len, sr.len ^ sr.len_x_code,
+            distance_code);
+      }
+      *num_literals += insert_length;
+      insert_length = 0;
+      /* Put the hash keys into the table, if there are enough bytes left.
+         Depending on the hasher implementation, it can push all positions
+         in the given range or only a subset of them. */
+      FN(StoreRange)(hasher, ringbuffer, ringbuffer_mask, position + 2,
+                     BROTLI_MIN(size_t, position + sr.len, store_end));
+      position += sr.len;
+    } else {
+      ++insert_length;
+      ++position;
+      /* If we have not seen matches for a long time, we can skip some
+         match lookups. Unsuccessful match lookups are very very expensive
+         and this kind of a heuristic speeds up compression quite
+         a lot. */
+      if (position > apply_random_heuristics) {
+        /* Going through uncompressible data, jump. */
+        if (position >
+            apply_random_heuristics + 4 * random_heuristics_window_size) {
+          /* It is quite a long time since we saw a copy, so we assume
+             that this data is not compressible, and store hashes less
+             often. Hashes of non compressible data are less likely to
+             turn out to be useful in the future, too, so we store less of
+             them to not to flood out the hash table of good compressible
+             data. */
+          const size_t kMargin =
+              BROTLI_MAX(size_t, FN(StoreLookahead)() - 1, 4);
+          size_t pos_jump =
+              BROTLI_MIN(size_t, position + 16, pos_end - kMargin);
+          for (; position < pos_jump; position += 4) {
+            FN(Store)(hasher, ringbuffer, ringbuffer_mask, position);
+            insert_length += 4;
+          }
+        } else {
+          const size_t kMargin =
+              BROTLI_MAX(size_t, FN(StoreLookahead)() - 1, 2);
+          size_t pos_jump =
+              BROTLI_MIN(size_t, position + 8, pos_end - kMargin);
+          for (; position < pos_jump; position += 2) {
+            FN(Store)(hasher, ringbuffer, ringbuffer_mask, position);
+            insert_length += 2;
+          }
+        }
+      }
+    }
+  }
+  insert_length += pos_end - position;
+  *last_insert_len = insert_length;
+  *num_commands += (size_t)(commands - orig_commands);
+}
+
+#undef Hasher