Added brotli enc/ and tools/ directories.

third_party/brotli/enc/histogram.cc

+/* Copyright 2013 Google Inc. All Rights Reserved.
+
+   Distributed under MIT license.
+   See file LICENSE for detail or copy at https://opensource.org/licenses/MIT
+*/
+
+// Build per-context histograms of literals, commands and distance codes.
+
+#include "./histogram.h"
+
+#include <cmath>
+
+#include "./block_splitter.h"
+#include "./command.h"
+#include "./context.h"
+#include "./prefix.h"
+
+namespace brotli {
+
+void BuildHistograms(
+    const Command* cmds,
+    const size_t num_commands,
+    const BlockSplit& literal_split,
+    const BlockSplit& insert_and_copy_split,
+    const BlockSplit& dist_split,
+    const uint8_t* ringbuffer,
+    size_t start_pos,
+    size_t mask,
+    uint8_t prev_byte,
+    uint8_t prev_byte2,
+    const std::vector<ContextType>& context_modes,
+    std::vector<HistogramLiteral>* literal_histograms,
+    std::vector<HistogramCommand>* insert_and_copy_histograms,
+    std::vector<HistogramDistance>* copy_dist_histograms) {
+  size_t pos = start_pos;
+  BlockSplitIterator literal_it(literal_split);
+  BlockSplitIterator insert_and_copy_it(insert_and_copy_split);
+  BlockSplitIterator dist_it(dist_split);
+  for (size_t i = 0; i < num_commands; ++i) {
+    const Command &cmd = cmds[i];
+    insert_and_copy_it.Next();
+    (*insert_and_copy_histograms)[insert_and_copy_it.type_].Add(
+        cmd.cmd_prefix_);
+    for (size_t j = cmd.insert_len_; j != 0; --j) {
+      literal_it.Next();
+      size_t context = (literal_it.type_ << kLiteralContextBits) +
+          Context(prev_byte, prev_byte2, context_modes[literal_it.type_]);
+      (*literal_histograms)[context].Add(ringbuffer[pos & mask]);
+      prev_byte2 = prev_byte;
+      prev_byte = ringbuffer[pos & mask];
+      ++pos;
+    }
+    pos += cmd.copy_len();
+    if (cmd.copy_len()) {
+      prev_byte2 = ringbuffer[(pos - 2) & mask];
+      prev_byte = ringbuffer[(pos - 1) & mask];
+      if (cmd.cmd_prefix_ >= 128) {
+        dist_it.Next();
+        size_t context = (dist_it.type_ << kDistanceContextBits) +
+            cmd.DistanceContext();
+        (*copy_dist_histograms)[context].Add(cmd.dist_prefix_);
+      }
+    }
+  }
+}
+
+}  // namespace brotli