Add brotli compressor

This commit is for the encoder for brotli compression format. Brotli is a generic byte-level compression algorithm.
2013-10-23 13:06:13 +02:00
parent b35077ca42
commit 79e99afe46
24 changed files with 3904 additions and 0 deletions
@@ -0,0 +1,72 @@
+// Copyright 2013 Google Inc. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// Build per-context histograms of literals, commands and distance codes.
+
+#include "./histogram.h"
+
+#include <stdint.h>
+#include <cmath>
+
+#include "./block_splitter.h"
+#include "./command.h"
+#include "./context.h"
+#include "./prefix.h"
+
+namespace brotli {
+
+void BuildHistograms(
+    const std::vector<Command>& cmds,
+    const BlockSplit& literal_split,
+    const BlockSplit& insert_and_copy_split,
+    const BlockSplit& dist_split,
+    const uint8_t* input_buffer,
+    size_t pos,
+    int context_mode,
+    int distance_context_mode,
+    std::vector<HistogramLiteral>* literal_histograms,
+    std::vector<HistogramCommand>* insert_and_copy_histograms,
+    std::vector<HistogramDistance>* copy_dist_histograms) {
+  BlockSplitIterator literal_it(literal_split);
+  BlockSplitIterator insert_and_copy_it(insert_and_copy_split);
+  BlockSplitIterator dist_it(dist_split);
+  for (int i = 0; i < cmds.size(); ++i) {
+    const Command &cmd = cmds[i];
+    insert_and_copy_it.Next();
+    (*insert_and_copy_histograms)[insert_and_copy_it.type_].Add(
+        cmd.command_prefix_);
+    for (int j = 0; j < cmd.insert_length_; ++j) {
+      literal_it.Next();
+      uint8_t prev_byte = pos > 0 ? input_buffer[pos - 1] : 0;
+      uint8_t prev_byte2 = pos > 1 ? input_buffer[pos - 2] : 0;
+      uint8_t prev_byte3 = pos > 2 ? input_buffer[pos - 3] : 0;
+      int context = (literal_it.type_ * NumContexts(context_mode) +
+                     Context(prev_byte, prev_byte2, prev_byte3, context_mode));
+      (*literal_histograms)[context].Add(input_buffer[pos]);
+      ++pos;
+    }
+    pos += cmd.copy_length_;
+    if (cmd.copy_length_ > 0 && cmd.distance_prefix_ != 0xffff) {
+      dist_it.Next();
+      int context = dist_it.type_;
+      if (distance_context_mode > 0) {
+        context <<= 2;
+        context += (cmd.copy_length_ > 4) ? 3 : cmd.copy_length_ - 2;
+      }
+      (*copy_dist_histograms)[context].Add(cmd.distance_prefix_);
+    }
+  }
+}
+
+}  // namespace brotli