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77 lines
2.5 KiB
77 lines
2.5 KiB
2 years ago
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// Copyright 2013 Google Inc. All Rights Reserved.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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//
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// Build per-context histograms of literals, commands and distance codes.
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#include "./histogram.h"
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#include <stdint.h>
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#include <cmath>
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#include "./block_splitter.h"
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#include "./command.h"
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#include "./context.h"
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#include "./prefix.h"
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namespace brotli {
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void BuildHistograms(
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const Command* cmds,
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const size_t num_commands,
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const BlockSplit& literal_split,
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const BlockSplit& insert_and_copy_split,
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const BlockSplit& dist_split,
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const uint8_t* ringbuffer,
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size_t start_pos,
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size_t mask,
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uint8_t prev_byte,
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uint8_t prev_byte2,
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const std::vector<int>& context_modes,
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std::vector<HistogramLiteral>* literal_histograms,
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std::vector<HistogramCommand>* insert_and_copy_histograms,
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std::vector<HistogramDistance>* copy_dist_histograms) {
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size_t pos = start_pos;
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BlockSplitIterator literal_it(literal_split);
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BlockSplitIterator insert_and_copy_it(insert_and_copy_split);
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BlockSplitIterator dist_it(dist_split);
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for (int i = 0; i < num_commands; ++i) {
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const Command &cmd = cmds[i];
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insert_and_copy_it.Next();
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(*insert_and_copy_histograms)[insert_and_copy_it.type_].Add(
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cmd.cmd_prefix_);
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for (int j = 0; j < cmd.insert_len_; ++j) {
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literal_it.Next();
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int context = (literal_it.type_ << kLiteralContextBits) +
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Context(prev_byte, prev_byte2, context_modes[literal_it.type_]);
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(*literal_histograms)[context].Add(ringbuffer[pos & mask]);
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prev_byte2 = prev_byte;
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prev_byte = ringbuffer[pos & mask];
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++pos;
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}
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pos += cmd.copy_len_;
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if (cmd.copy_len_ > 0) {
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prev_byte2 = ringbuffer[(pos - 2) & mask];
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prev_byte = ringbuffer[(pos - 1) & mask];
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if (cmd.cmd_prefix_ >= 128) {
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dist_it.Next();
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int context = (dist_it.type_ << kDistanceContextBits) +
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cmd.DistanceContext();
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(*copy_dist_histograms)[context].Add(cmd.dist_prefix_);
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}
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}
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}
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}
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} // namespace brotli
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