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101 lines
3.2 KiB
C
101 lines
3.2 KiB
C
/* Copyright 2013 Google Inc. All Rights Reserved.
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Distributed under MIT license.
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See file LICENSE for detail or copy at https://opensource.org/licenses/MIT
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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 "../common/context.h"
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#include "block_splitter.h"
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#include "command.h"
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#if defined(__cplusplus) || defined(c_plusplus)
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extern "C" {
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#endif
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typedef struct BlockSplitIterator {
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const BlockSplit* split_; /* Not owned. */
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size_t idx_;
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size_t type_;
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size_t length_;
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} BlockSplitIterator;
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static void InitBlockSplitIterator(BlockSplitIterator* self,
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const BlockSplit* split) {
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self->split_ = split;
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self->idx_ = 0;
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self->type_ = 0;
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self->length_ = split->lengths ? split->lengths[0] : 0;
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}
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static void BlockSplitIteratorNext(BlockSplitIterator* self) {
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if (self->length_ == 0) {
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++self->idx_;
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self->type_ = self->split_->types[self->idx_];
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self->length_ = self->split_->lengths[self->idx_];
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}
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--self->length_;
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}
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void BrotliBuildHistogramsWithContext(
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const Command* cmds, const size_t num_commands,
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const BlockSplit* literal_split, const BlockSplit* insert_and_copy_split,
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const BlockSplit* dist_split, const uint8_t* ringbuffer, size_t start_pos,
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size_t mask, uint8_t prev_byte, uint8_t prev_byte2,
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const ContextType* context_modes, HistogramLiteral* literal_histograms,
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HistogramCommand* insert_and_copy_histograms,
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HistogramDistance* copy_dist_histograms) {
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size_t pos = start_pos;
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BlockSplitIterator literal_it;
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BlockSplitIterator insert_and_copy_it;
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BlockSplitIterator dist_it;
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size_t i;
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InitBlockSplitIterator(&literal_it, literal_split);
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InitBlockSplitIterator(&insert_and_copy_it, insert_and_copy_split);
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InitBlockSplitIterator(&dist_it, dist_split);
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for (i = 0; i < num_commands; ++i) {
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const Command* cmd = &cmds[i];
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size_t j;
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BlockSplitIteratorNext(&insert_and_copy_it);
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HistogramAddCommand(&insert_and_copy_histograms[insert_and_copy_it.type_],
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cmd->cmd_prefix_);
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/* TODO(eustas): unwrap iterator blocks. */
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for (j = cmd->insert_len_; j != 0; --j) {
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size_t context;
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BlockSplitIteratorNext(&literal_it);
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context = literal_it.type_;
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if (context_modes) {
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ContextLut lut = BROTLI_CONTEXT_LUT(context_modes[context]);
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context = (context << BROTLI_LITERAL_CONTEXT_BITS) +
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BROTLI_CONTEXT(prev_byte, prev_byte2, lut);
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}
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HistogramAddLiteral(&literal_histograms[context],
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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 += CommandCopyLen(cmd);
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if (CommandCopyLen(cmd)) {
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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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size_t context;
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BlockSplitIteratorNext(&dist_it);
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context = (dist_it.type_ << BROTLI_DISTANCE_CONTEXT_BITS) +
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CommandDistanceContext(cmd);
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HistogramAddDistance(©_dist_histograms[context],
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cmd->dist_prefix_ & 0x3FF);
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}
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}
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}
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}
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#if defined(__cplusplus) || defined(c_plusplus)
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} /* extern "C" */
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#endif
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