forked from andybalholm/brotli
-
Notifications
You must be signed in to change notification settings - Fork 0
/
metablock_command.go
162 lines (146 loc) · 5.98 KB
/
metablock_command.go
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
package brotli
/* Copyright 2015 Google Inc. All Rights Reserved.
Distributed under MIT license.
See file LICENSE for detail or copy at https://opensource.org/licenses/MIT
*/
/* Greedy block splitter for one block category (literal, command or distance).
*/
type blockSplitterCommand struct {
alphabet_size_ uint
min_block_size_ uint
split_threshold_ float64
num_blocks_ uint
split_ *blockSplit
histograms_ []histogramCommand
histograms_size_ *uint
target_block_size_ uint
block_size_ uint
curr_histogram_ix_ uint
last_histogram_ix_ [2]uint
last_entropy_ [2]float64
merge_last_count_ uint
}
func initBlockSplitterCommand(self *blockSplitterCommand, alphabet_size uint, min_block_size uint, split_threshold float64, num_symbols uint, split *blockSplit, histograms *[]histogramCommand, histograms_size *uint) {
var max_num_blocks uint = num_symbols/min_block_size + 1
var max_num_types uint = brotli_min_size_t(max_num_blocks, maxNumberOfBlockTypes+1)
/* We have to allocate one more histogram than the maximum number of block
types for the current histogram when the meta-block is too big. */
self.alphabet_size_ = alphabet_size
self.min_block_size_ = min_block_size
self.split_threshold_ = split_threshold
self.num_blocks_ = 0
self.split_ = split
self.histograms_size_ = histograms_size
self.target_block_size_ = min_block_size
self.block_size_ = 0
self.curr_histogram_ix_ = 0
self.merge_last_count_ = 0
brotli_ensure_capacity_uint8_t(&split.types, &split.types_alloc_size, max_num_blocks)
brotli_ensure_capacity_uint32_t(&split.lengths, &split.lengths_alloc_size, max_num_blocks)
self.split_.num_blocks = max_num_blocks
assert(*histograms == nil)
*histograms_size = max_num_types
*histograms = make([]histogramCommand, (*histograms_size))
self.histograms_ = *histograms
/* Clear only current histogram. */
histogramClearCommand(&self.histograms_[0])
self.last_histogram_ix_[1] = 0
self.last_histogram_ix_[0] = self.last_histogram_ix_[1]
}
/* Does either of three things:
(1) emits the current block with a new block type;
(2) emits the current block with the type of the second last block;
(3) merges the current block with the last block. */
func blockSplitterFinishBlockCommand(self *blockSplitterCommand, is_final bool) {
var split *blockSplit = self.split_
var last_entropy []float64 = self.last_entropy_[:]
var histograms []histogramCommand = self.histograms_
self.block_size_ = brotli_max_size_t(self.block_size_, self.min_block_size_)
if self.num_blocks_ == 0 {
/* Create first block. */
split.lengths[0] = uint32(self.block_size_)
split.types[0] = 0
last_entropy[0] = bitsEntropy(histograms[0].data_[:], self.alphabet_size_)
last_entropy[1] = last_entropy[0]
self.num_blocks_++
split.num_types++
self.curr_histogram_ix_++
if self.curr_histogram_ix_ < *self.histograms_size_ {
histogramClearCommand(&histograms[self.curr_histogram_ix_])
}
self.block_size_ = 0
} else if self.block_size_ > 0 {
var entropy float64 = bitsEntropy(histograms[self.curr_histogram_ix_].data_[:], self.alphabet_size_)
var combined_histo [2]histogramCommand
var combined_entropy [2]float64
var diff [2]float64
var j uint
for j = 0; j < 2; j++ {
var last_histogram_ix uint = self.last_histogram_ix_[j]
combined_histo[j] = histograms[self.curr_histogram_ix_]
histogramAddHistogramCommand(&combined_histo[j], &histograms[last_histogram_ix])
combined_entropy[j] = bitsEntropy(combined_histo[j].data_[0:], self.alphabet_size_)
diff[j] = combined_entropy[j] - entropy - last_entropy[j]
}
if split.num_types < maxNumberOfBlockTypes && diff[0] > self.split_threshold_ && diff[1] > self.split_threshold_ {
/* Create new block. */
split.lengths[self.num_blocks_] = uint32(self.block_size_)
split.types[self.num_blocks_] = byte(split.num_types)
self.last_histogram_ix_[1] = self.last_histogram_ix_[0]
self.last_histogram_ix_[0] = uint(byte(split.num_types))
last_entropy[1] = last_entropy[0]
last_entropy[0] = entropy
self.num_blocks_++
split.num_types++
self.curr_histogram_ix_++
if self.curr_histogram_ix_ < *self.histograms_size_ {
histogramClearCommand(&histograms[self.curr_histogram_ix_])
}
self.block_size_ = 0
self.merge_last_count_ = 0
self.target_block_size_ = self.min_block_size_
} else if diff[1] < diff[0]-20.0 {
split.lengths[self.num_blocks_] = uint32(self.block_size_)
split.types[self.num_blocks_] = split.types[self.num_blocks_-2]
/* Combine this block with second last block. */
var tmp uint = self.last_histogram_ix_[0]
self.last_histogram_ix_[0] = self.last_histogram_ix_[1]
self.last_histogram_ix_[1] = tmp
histograms[self.last_histogram_ix_[0]] = combined_histo[1]
last_entropy[1] = last_entropy[0]
last_entropy[0] = combined_entropy[1]
self.num_blocks_++
self.block_size_ = 0
histogramClearCommand(&histograms[self.curr_histogram_ix_])
self.merge_last_count_ = 0
self.target_block_size_ = self.min_block_size_
} else {
/* Combine this block with last block. */
split.lengths[self.num_blocks_-1] += uint32(self.block_size_)
histograms[self.last_histogram_ix_[0]] = combined_histo[0]
last_entropy[0] = combined_entropy[0]
if split.num_types == 1 {
last_entropy[1] = last_entropy[0]
}
self.block_size_ = 0
histogramClearCommand(&histograms[self.curr_histogram_ix_])
self.merge_last_count_++
if self.merge_last_count_ > 1 {
self.target_block_size_ += self.min_block_size_
}
}
}
if is_final {
*self.histograms_size_ = split.num_types
split.num_blocks = self.num_blocks_
}
}
/* Adds the next symbol to the current histogram. When the current histogram
reaches the target size, decides on merging the block. */
func blockSplitterAddSymbolCommand(self *blockSplitterCommand, symbol uint) {
histogramAddCommand(&self.histograms_[self.curr_histogram_ix_], symbol)
self.block_size_++
if self.block_size_ == self.target_block_size_ {
blockSplitterFinishBlockCommand(self, false) /* is_final = */
}
}