Update brotli to v1.0.0-snapshot.

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