tor-browser

The Tor Browser
git clone https://git.dasho.dev/tor-browser.git
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histogram.c (3261B)

      1 /* Copyright 2013 Google Inc. All Rights Reserved.
      2 
      3   Distributed under MIT license.
      4   See file LICENSE for detail or copy at https://opensource.org/licenses/MIT
      5 */
      6 
      7 /* Build per-context histograms of literals, commands and distance codes. */
      8 
      9 #include "histogram.h"
     10 
     11 #include "../common/context.h"
     12 #include "../common/platform.h"
     13 #include "block_splitter.h"
     14 #include "command.h"
     15 
     16 #if defined(__cplusplus) || defined(c_plusplus)
     17 extern "C" {
     18 #endif
     19 
     20 typedef struct BlockSplitIterator {
     21  const BlockSplit* split_;  /* Not owned. */
     22  size_t idx_;
     23  size_t type_;
     24  size_t length_;
     25 } BlockSplitIterator;
     26 
     27 static void InitBlockSplitIterator(BlockSplitIterator* self,
     28    const BlockSplit* split) {
     29  self->split_ = split;
     30  self->idx_ = 0;
     31  self->type_ = 0;
     32  self->length_ = split->lengths ? split->lengths[0] : 0;
     33 }
     34 
     35 static void BlockSplitIteratorNext(BlockSplitIterator* self) {
     36  if (self->length_ == 0) {
     37    ++self->idx_;
     38    self->type_ = self->split_->types[self->idx_];
     39    self->length_ = self->split_->lengths[self->idx_];
     40  }
     41  --self->length_;
     42 }
     43 
     44 void BrotliBuildHistogramsWithContext(
     45    const Command* cmds, const size_t num_commands,
     46    const BlockSplit* literal_split, const BlockSplit* insert_and_copy_split,
     47    const BlockSplit* dist_split, const uint8_t* ringbuffer, size_t start_pos,
     48    size_t mask, uint8_t prev_byte, uint8_t prev_byte2,
     49    const ContextType* context_modes, HistogramLiteral* literal_histograms,
     50    HistogramCommand* insert_and_copy_histograms,
     51    HistogramDistance* copy_dist_histograms) {
     52  size_t pos = start_pos;
     53  BlockSplitIterator literal_it;
     54  BlockSplitIterator insert_and_copy_it;
     55  BlockSplitIterator dist_it;
     56  size_t i;
     57 
     58  InitBlockSplitIterator(&literal_it, literal_split);
     59  InitBlockSplitIterator(&insert_and_copy_it, insert_and_copy_split);
     60  InitBlockSplitIterator(&dist_it, dist_split);
     61  for (i = 0; i < num_commands; ++i) {
     62    const Command* cmd = &cmds[i];
     63    size_t j;
     64    BlockSplitIteratorNext(&insert_and_copy_it);
     65    HistogramAddCommand(&insert_and_copy_histograms[insert_and_copy_it.type_],
     66        cmd->cmd_prefix_);
     67    /* TODO(eustas): unwrap iterator blocks. */
     68    for (j = cmd->insert_len_; j != 0; --j) {
     69      size_t context;
     70      BlockSplitIteratorNext(&literal_it);
     71      context = literal_it.type_;
     72      if (context_modes) {
     73        ContextLut lut = BROTLI_CONTEXT_LUT(context_modes[context]);
     74        context = (context << BROTLI_LITERAL_CONTEXT_BITS) +
     75            BROTLI_CONTEXT(prev_byte, prev_byte2, lut);
     76      }
     77      HistogramAddLiteral(&literal_histograms[context],
     78          ringbuffer[pos & mask]);
     79      prev_byte2 = prev_byte;
     80      prev_byte = ringbuffer[pos & mask];
     81      ++pos;
     82    }
     83    pos += CommandCopyLen(cmd);
     84    if (CommandCopyLen(cmd)) {
     85      prev_byte2 = ringbuffer[(pos - 2) & mask];
     86      prev_byte = ringbuffer[(pos - 1) & mask];
     87      if (cmd->cmd_prefix_ >= 128) {
     88        size_t context;
     89        BlockSplitIteratorNext(&dist_it);
     90        context = (dist_it.type_ << BROTLI_DISTANCE_CONTEXT_BITS) +
     91            CommandDistanceContext(cmd);
     92        HistogramAddDistance(&copy_dist_histograms[context],
     93            cmd->dist_prefix_ & 0x3FF);
     94      }
     95    }
     96  }
     97 }
     98 
     99 #if defined(__cplusplus) || defined(c_plusplus)
    100 }  /* extern "C" */
    101 #endif