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/* 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 "../common/context.h"
#include "./block_splitter.h"
#include "./command.h"
#if defined(__cplusplus) || defined(c_plusplus)
extern "C" {
#endif
typedef struct BlockSplitIterator {
const BlockSplit* split_; /* Not owned. */
size_t idx_;
size_t type_;
size_t length_;
} BlockSplitIterator;
static void InitBlockSplitIterator(BlockSplitIterator* self,
const BlockSplit* split) {
self->split_ = split;
self->idx_ = 0;
self->type_ = 0;
self->length_ = split->lengths ? split->lengths[0] : 0;
}
static void BlockSplitIteratorNext(BlockSplitIterator* self) {
if (self->length_ == 0) {
++self->idx_;
self->type_ = self->split_->types[self->idx_];
self->length_ = self->split_->lengths[self->idx_];
}
--self->length_;
}
void BrotliBuildHistogramsWithContext(
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 ContextType* context_modes, HistogramLiteral* literal_histograms,
HistogramCommand* insert_and_copy_histograms,
HistogramDistance* copy_dist_histograms) {
size_t pos = start_pos;
BlockSplitIterator literal_it;
BlockSplitIterator insert_and_copy_it;
BlockSplitIterator dist_it;
size_t i;
InitBlockSplitIterator(&literal_it, literal_split);
InitBlockSplitIterator(&insert_and_copy_it, insert_and_copy_split);
InitBlockSplitIterator(&dist_it, dist_split);
for (i = 0; i < num_commands; ++i) {
const Command* cmd = &cmds[i];
size_t j;
BlockSplitIteratorNext(&insert_and_copy_it);
HistogramAddCommand(&insert_and_copy_histograms[insert_and_copy_it.type_],
cmd->cmd_prefix_);
/* TODO: unwrap iterator blocks. */
for (j = cmd->insert_len_; j != 0; --j) {
size_t context;
BlockSplitIteratorNext(&literal_it);
context = literal_it.type_;
if (context_modes) {
ContextLut lut = BROTLI_CONTEXT_LUT(context_modes[context]);
context = (context << BROTLI_LITERAL_CONTEXT_BITS) +
BROTLI_CONTEXT(prev_byte, prev_byte2, lut);
}
HistogramAddLiteral(&literal_histograms[context],
ringbuffer[pos & mask]);
prev_byte2 = prev_byte;
prev_byte = ringbuffer[pos & mask];
++pos;
}
pos += CommandCopyLen(cmd);
if (CommandCopyLen(cmd)) {
prev_byte2 = ringbuffer[(pos - 2) & mask];
prev_byte = ringbuffer[(pos - 1) & mask];
if (cmd->cmd_prefix_ >= 128) {
size_t context;
BlockSplitIteratorNext(&dist_it);
context = (dist_it.type_ << BROTLI_DISTANCE_CONTEXT_BITS) +
CommandDistanceContext(cmd);
HistogramAddDistance(©_dist_histograms[context],
cmd->dist_prefix_ & 0x3FF);
}
}
}
}
#if defined(__cplusplus) || defined(c_plusplus)
} /* extern "C" */
#endif
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