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 "./block_splitter.h"
13#include "./command.h"
14
15#if defined(__cplusplus) || defined(c_plusplus)
16extern "C" {
17#endif
18
19typedef struct BlockSplitIterator {
20  const BlockSplit* split_;  /* Not owned. */
21  size_t idx_;
22  size_t type_;
23  size_t length_;
24} BlockSplitIterator;
25
26static 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
34static 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
43void 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    /* TODO: unwrap iterator blocks. */
67    for (j = cmd->insert_len_; j != 0; --j) {
68      size_t context;
69      BlockSplitIteratorNext(&literal_it);
70      context = literal_it.type_;
71      if (context_modes) {
72        ContextLut lut = BROTLI_CONTEXT_LUT(context_modes[context]);
73        context = (context << BROTLI_LITERAL_CONTEXT_BITS) +
74            BROTLI_CONTEXT(prev_byte, prev_byte2, lut);
75      }
76      HistogramAddLiteral(&literal_histograms[context],
77          ringbuffer[pos & mask]);
78      prev_byte2 = prev_byte;
79      prev_byte = ringbuffer[pos & mask];
80      ++pos;
81    }
82    pos += CommandCopyLen(cmd);
83    if (CommandCopyLen(cmd)) {
84      prev_byte2 = ringbuffer[(pos - 2) & mask];
85      prev_byte = ringbuffer[(pos - 1) & mask];
86      if (cmd->cmd_prefix_ >= 128) {
87        size_t context;
88        BlockSplitIteratorNext(&dist_it);
89        context = (dist_it.type_ << BROTLI_DISTANCE_CONTEXT_BITS) +
90            CommandDistanceContext(cmd);
91        HistogramAddDistance(&copy_dist_histograms[context],
92            cmd->dist_prefix_ & 0x3FF);
93      }
94    }
95  }
96}
97
98#if defined(__cplusplus) || defined(c_plusplus)
99}  /* extern "C" */
100#endif
101