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
InitBlockSplitIterator(BlockSplitIterator * self,const BlockSplit * split)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
BlockSplitIteratorNext(BlockSplitIterator * self)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
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)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 = context_modes ?
70 ((literal_it.type_ << BROTLI_LITERAL_CONTEXT_BITS) +
71 Context(prev_byte, prev_byte2, context_modes[literal_it.type_])) :
72 literal_it.type_;
73 HistogramAddLiteral(&literal_histograms[context],
74 ringbuffer[pos & mask]);
75 prev_byte2 = prev_byte;
76 prev_byte = ringbuffer[pos & mask];
77 ++pos;
78 }
79 pos += CommandCopyLen(cmd);
80 if (CommandCopyLen(cmd)) {
81 prev_byte2 = ringbuffer[(pos - 2) & mask];
82 prev_byte = ringbuffer[(pos - 1) & mask];
83 if (cmd->cmd_prefix_ >= 128) {
84 size_t context;
85 BlockSplitIteratorNext(&dist_it);
86 context = (dist_it.type_ << BROTLI_DISTANCE_CONTEXT_BITS) +
87 CommandDistanceContext(cmd);
88 HistogramAddDistance(©_dist_histograms[context],
89 cmd->dist_prefix_);
90 }
91 }
92 }
93 }
94
95 #if defined(__cplusplus) || defined(c_plusplus)
96 } /* extern "C" */
97 #endif
98