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Updates to Brotli compression format, decoder and encoder

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This commit contains a batch of changes that were made to the Brotli
compression algorithm in the last month. Most important changes:

   * Fixes to the spec.
   * Change of code length code order.
   * Use a 2-level Huffman lookup table in the decoder.
   * Faster uncompressed meta-block decoding.
   * Optimized encoding of the Huffman code.
   * Detection of UTF-8 input encoding.
   * UTF-8 based literal cost modeling for improved
     backward reference selection.
This commit is contained in:
Zoltan Szabadka
2014-02-14 15:04:23 +01:00
parent dfc5a9f215
commit cbd5cb55f4
16 changed files with 912 additions and 635 deletions
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brotli/enc/hash.h
+9 -4
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@@ -150,7 +150,10 @@ class HashLongestMatch {
size_t * __restrict best_len_out,
size_t * __restrict best_len_code_out,
size_t * __restrict best_distance_out,
double * __restrict best_score_out) {
double * __restrict best_score_out,
bool * __restrict in_dictionary) {
*in_dictionary = true;
*best_len_code_out = 0;
const size_t cur_ix_masked = cur_ix & ring_buffer_mask;
const double start_cost4 = literal_cost == NULL ? 20 :
literal_cost[cur_ix_masked] +
@@ -166,9 +169,9 @@ class HashLongestMatch {
literal_cost[(cur_ix + 1) & ring_buffer_mask] + 1.2;
bool match_found = false;
// Don't accept a short copy from far away.
double best_score = 8.25;
double best_score = 8.11;
if (insert_length_ < 4) {
double cost_diff[4] = { 0.20, 0.09, 0.05, 0.03 };
double cost_diff[4] = { 0.10, 0.04, 0.02, 0.01 };
best_score += cost_diff[insert_length_];
}
size_t best_len = *best_len_out;
@@ -235,6 +238,7 @@ class HashLongestMatch {
*best_distance_out = best_ix;
*best_score_out = best_score;
match_found = true;
*in_dictionary = backward > max_backward;
}
}
}
@@ -257,7 +261,7 @@ class HashLongestMatch {
continue;
}
int len = 2;
const double score = start_cost2 - 1.70 * Log2Floor(backward);
const double score = start_cost2 - 2.3 * Log2Floor(backward);
if (best_score < score) {
best_score = score;
@@ -309,6 +313,7 @@ class HashLongestMatch {
*best_distance_out = best_ix;
*best_score_out = best_score;
match_found = true;
*in_dictionary = false;
}
}
}