BaseTools/Source/C/BrotliCompress/enc/histogram.c

   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 "./block_splitter.h"
  12 #include "./command.h"
  13 #include "./context.h"
  14
  15 #if defined(__cplusplus) || defined(c_plusplus)
  16 extern "C" {
  17 #endif
  18
  19 typedef struct BlockSplitIterator {
  20   const BlockSplit* split_;  /* Not owned. */
  21   size_t idx_;
  22   size_t type_;
  23   size_t length_;
  24 } BlockSplitIterator;
  25
  26 static void InitBlockSplitIterator(BlockSplitIterator* self,
  27     const BlockSplit* split) {
  28   self->split_ = split;
  29   self->idx_ = 0;
  30   self->type_ = 0;
  31   self->length_ = split->lengths ? split->lengths[0] : 0;
  32 }
  33
  34 static void BlockSplitIteratorNext(BlockSplitIterator* self) {
  35   if (self->length_ == 0) {
  36     ++self->idx_;
  37     self->type_ = self->split_->types[self->idx_];
  38     self->length_ = self->split_->lengths[self->idx_];
  39   }
  40   --self->length_;
  41 }
  42
  43 void BrotliBuildHistogramsWithContext(
  44     const Command* cmds, const size_t num_commands,
  45     const BlockSplit* literal_split, const BlockSplit* insert_and_copy_split,
  46     const BlockSplit* dist_split, const uint8_t* ringbuffer, size_t start_pos,
  47     size_t mask, uint8_t prev_byte, uint8_t prev_byte2,
  48     const ContextType* context_modes, HistogramLiteral* literal_histograms,
  49     HistogramCommand* insert_and_copy_histograms,
  50     HistogramDistance* copy_dist_histograms) {
  51   size_t pos = start_pos;
  52   BlockSplitIterator literal_it;
  53   BlockSplitIterator insert_and_copy_it;
  54   BlockSplitIterator dist_it;
  55   size_t i;
  56
  57   InitBlockSplitIterator(&literal_it, literal_split);
  58   InitBlockSplitIterator(&insert_and_copy_it, insert_and_copy_split);
  59   InitBlockSplitIterator(&dist_it, dist_split);
  60   for (i = 0; i < num_commands; ++i) {
  61     const Command* cmd = &cmds[i];
  62     size_t j;
  63     BlockSplitIteratorNext(&insert_and_copy_it);
  64     HistogramAddCommand(&insert_and_copy_histograms[insert_and_copy_it.type_],
  65         cmd->cmd_prefix_);
  66     for (j = cmd->insert_len_; j != 0; --j) {
  67       size_t context;
  68       BlockSplitIteratorNext(&literal_it);
  69       context = (literal_it.type_ << BROTLI_LITERAL_CONTEXT_BITS) +
  70           Context(prev_byte, prev_byte2, context_modes[literal_it.type_]);
  71       HistogramAddLiteral(&literal_histograms[context],
  72           ringbuffer[pos & mask]);
  73       prev_byte2 = prev_byte;
  74       prev_byte = ringbuffer[pos & mask];
  75       ++pos;
  76     }
  77     pos += CommandCopyLen(cmd);
  78     if (CommandCopyLen(cmd)) {
  79       prev_byte2 = ringbuffer[(pos - 2) & mask];
  80       prev_byte = ringbuffer[(pos - 1) & mask];
  81       if (cmd->cmd_prefix_ >= 128) {
  82         size_t context;
  83         BlockSplitIteratorNext(&dist_it);
  84         context = (dist_it.type_ << BROTLI_DISTANCE_CONTEXT_BITS) +
  85             CommandDistanceContext(cmd);
  86         HistogramAddDistance(&copy_dist_histograms[context],
  87             cmd->dist_prefix_);
  88       }
  89     }
  90   }
  91 }
  92
  93 #if defined(__cplusplus) || defined(c_plusplus)
  94 }  /* extern "C" */
  95 #endif