Coverage Report

Created: 2025-06-12 06:11

/src/brunsli/c/common/context.h
Line
Count
Source (jump to first uncovered line)
1
// Copyright (c) Google LLC 2019
2
//
3
// Use of this source code is governed by an MIT-style
4
// license that can be found in the LICENSE file or at
5
// https://opensource.org/licenses/MIT.
6
7
#ifndef BRUNSLI_COMMON_CONTEXT_H_
8
#define BRUNSLI_COMMON_CONTEXT_H_
9
10
#include <vector>
11
12
#include "./distributions.h"
13
#include <brunsli/jpeg_data.h>
14
#include "./platform.h"
15
#include <brunsli/types.h>
16
17
namespace brunsli {
18
19
static const size_t kMaxAverageContext = 8;
20
static const size_t kNumAvrgContexts = kMaxAverageContext + 1u;
21
// 6 bits allow encoding values 0..63; this range represents the possible
22
// quantities of non-zero AC coefficients in the DCT block.
23
static const size_t kNumNonZeroBits = 6u;
24
/**
25
 * "number of non-zeros" value is decoded as a series of bits,
26
 * highest to lowest.
27
 *
28
 * Partially decoded value is used as a context for reading the next bit.
29
 * Contexts are organized in a binary tree. There are 64 final values, thus
30
 * there are 1-less non-leaf nodes.
31
 * Also, this constant also denotes the maximal value that could be encoded.
32
 *
33
 * static_assert(kNumNonZeroTreeSize == kDCTBlockSize - 1u)
34
 */
35
static const size_t kNumNonZeroTreeSize = (1u << kNumNonZeroBits) - 1u;
36
static const size_t kNumNonZeroQuant = 2u;
37
static const size_t kNumNonZeroContextMax =
38
    kNumNonZeroTreeSize / kNumNonZeroQuant;
39
static const size_t kNumNonZeroContextCount = kNumNonZeroContextMax + 1u;
40
41
static const uint8_t kNonzeroBuckets[64] = {
42
    0,  1,  2,  3,  4,  4,  5,  5,  5,  6,  6,  6,  6,  7,  7,  7,
43
    7,  7,  7,  7,  7,  8,  8,  8,  8,  8,  8,  8,  8,  8,  8,  8,
44
    9,  9,  9,  9,  9,  9,  9,  9,  9,  9,  9,  9,  9,  10, 10, 10,
45
    10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10,
46
};
47
// kNonzeroBuckets[i] < kNumNonzeroBuckets
48
static const uint8_t kNumNonzeroBuckets = 11;
49
50
static const int kNumSchemes = 7;
51
52
static const uint8_t kFreqContext[kNumSchemes][64] = {
53
    {
54
        0,
55
    },
56
57
    {
58
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
59
        0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
60
        1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0,
61
    },
62
63
    {
64
        0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
65
        2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3,
66
        3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 1, 1, 1,
67
    },
68
69
    {
70
        0, 1, 1, 2, 2, 2, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 5, 5, 5, 5, 5, 5,
71
        5, 5, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 7, 7, 7, 7,
72
        7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 2, 2, 2,
73
    },
74
75
    {
76
        0,  1,  2,  3,  4,  4,  5,  5,  6,  6,  7,  7,  8,  8,  8,  8,
77
        9,  9,  9,  9,  10, 10, 10, 10, 11, 11, 11, 11, 12, 12, 12, 12,
78
        13, 13, 13, 13, 13, 13, 13, 13, 14, 14, 14, 14, 14, 14, 14, 14,
79
        15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
80
    },
81
82
    {
83
        0,  1,  2,  3,  4,  5,  6,  7,  8,  9,  10, 11, 12, 13, 14, 15,
84
        16, 16, 17, 17, 18, 18, 19, 19, 20, 20, 21, 21, 22, 22, 23, 23,
85
        24, 24, 24, 24, 25, 25, 25, 25, 26, 26, 26, 26, 27, 27, 27, 27,
86
        28, 28, 28, 28, 29, 29, 29, 29, 30, 30, 30, 30, 31, 31, 31, 31,
87
    },
88
89
    {
90
        0,  1,  2,  3,  4,  5,  6,  7,  8,  9,  10, 11, 12, 13, 14, 15,
91
        16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31,
92
        32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47,
93
        48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63,
94
    },
95
};
96
97
static const uint16_t kNumNonzeroContext[kNumSchemes][64] = {
98
    {0, 1, 1, 2, 2, 2, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 5, 5, 5, 5, 5, 5,
99
     5, 5, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 7, 7, 7, 7,
100
     7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7},
101
    {0,  2,  2,  4,  4,  4,  6,  6,  6,  6,  8,  8,  8,  8,  8,  8,
102
     10, 10, 10, 10, 10, 10, 10, 10, 12, 12, 12, 12, 12, 12, 12, 12,
103
     12, 12, 12, 12, 12, 12, 12, 12, 14, 14, 14, 14, 14, 14, 14, 14,
104
     14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14},
105
    {0,  4,  4,  8,  8,  8,  12, 12, 12, 12, 16, 16, 16, 16, 16, 16,
106
     20, 20, 20, 20, 20, 20, 20, 20, 24, 24, 24, 24, 24, 24, 24, 24,
107
     24, 24, 24, 24, 24, 24, 24, 24, 28, 28, 28, 28, 28, 28, 28, 28,
108
     28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28},
109
    {0,  8,  8,  16, 16, 16, 24, 24, 24, 24, 32, 32, 32, 32, 32, 32,
110
     40, 40, 40, 40, 40, 40, 40, 40, 48, 48, 48, 48, 48, 48, 48, 48,
111
     48, 48, 48, 48, 48, 48, 48, 48, 55, 55, 55, 55, 55, 55, 55, 55,
112
     55, 55, 55, 55, 55, 55, 55, 55, 55, 55, 55, 55, 55, 55, 55, 55},
113
    {0,   16,  16,  32,  32,  32,  48,  48,  48,  48,  64,  64,  64,
114
     64,  64,  64,  80,  80,  80,  80,  80,  80,  80,  80,  95,  95,
115
     95,  95,  95,  95,  95,  95,  95,  95,  95,  95,  95,  95,  95,
116
     95,  109, 109, 109, 109, 109, 109, 109, 109, 109, 109, 109, 109,
117
     109, 109, 109, 109, 109, 109, 109, 109, 109, 109, 109, 109},
118
    {0,   32,  32,  64,  64,  64,  96,  96,  96,  96,  127, 127, 127,
119
     127, 127, 127, 157, 157, 157, 157, 157, 157, 157, 157, 185, 185,
120
     185, 185, 185, 185, 185, 185, 185, 185, 185, 185, 185, 185, 185,
121
     185, 211, 211, 211, 211, 211, 211, 211, 211, 211, 211, 211, 211,
122
     211, 211, 211, 211, 211, 211, 211, 211, 211, 211, 211, 211},
123
    {0,   64,  64,  127, 127, 127, 188, 188, 188, 188, 246, 246, 246,
124
     246, 246, 246, 300, 300, 300, 300, 300, 300, 300, 300, 348, 348,
125
     348, 348, 348, 348, 348, 348, 348, 348, 348, 348, 348, 348, 348,
126
     348, 388, 388, 388, 388, 388, 388, 388, 388, 388, 388, 388, 388,
127
     388, 388, 388, 388, 388, 388, 388, 388, 388, 388, 388, 388}};
128
129
static const uint16_t kNumNonzeroContextSkip[kNumSchemes] = {8,   15,  31, 61,
130
                                                             120, 231, 412};
131
132
/**
133
 * Table that specifies, how context is calculated.
134
 *
135
 * Each value corresponds to DCT coefficient and is a sum of flags:
136
 *  - 1: context should be calculated using ACPredictContextRow
137
 *  - 2: context should be calculated using ACPredictContextCol
138
 */
139
static const uint8_t kContextAlgorithm[128] = {
140
    // JPEG XL layout
141
    0, 1, 1, 1, 1, 0, 0, 0,  //
142
    2, 3, 1, 1, 1, 0, 0, 0,  //
143
    2, 2, 0, 0, 0, 0, 0, 0,  //
144
    2, 2, 0, 0, 0, 0, 0, 0,  //
145
    2, 2, 0, 0, 0, 0, 0, 0,  //
146
    0, 0, 0, 0, 0, 0, 0, 0,  //
147
    0, 0, 0, 0, 0, 0, 0, 0,  //
148
    0, 0, 0, 0, 0, 0, 0, 0,
149
    // Legacy layout
150
    0, 1, 1, 1, 1, 1, 1, 1,  //
151
    2, 0, 0, 0, 0, 0, 0, 0,  //
152
    2, 0, 0, 0, 0, 0, 0, 0,  //
153
    2, 0, 0, 0, 0, 0, 0, 0,  //
154
    2, 0, 0, 0, 0, 0, 0, 0,  //
155
    2, 0, 0, 0, 0, 0, 0, 0,  //
156
    2, 0, 0, 0, 0, 0, 0, 0,  //
157
    2, 0, 0, 0, 0, 0, 0, 0,
158
};
159
160
inline uint16_t ZeroDensityContext(size_t nonzeros_left, size_t k,
161
7.63M
                                   size_t bits) {
162
7.63M
  return kNumNonzeroContext[bits][nonzeros_left] + kFreqContext[bits][k];
163
7.63M
}
164
165
// Returns the context for the absolute value of the prediction error of
166
// the next DC coefficient in column x, using the one row size ringbuffer of
167
// previous absolute prediction errors in vals.
168
2.37M
inline int WeightedAverageContextDC(const int* vals, int x) {
169
  // Since vals is a ringbuffer, vals[x] and vals[x + 1] refer to the
170
  // previous row.
171
2.37M
  int sum = 1 + vals[x - 2] + vals[x - 1] + vals[x] + vals[x + 1];
172
2.37M
  if ((sum >> kMaxAverageContext) != 0) {
173
360k
    return kMaxAverageContext;
174
360k
  }
175
2.01M
  return Log2FloorNonZero(sum);
176
2.37M
}
177
178
/**
179
 * Calculates the context on the base of average of already decoded
180
 * neighbour values.
181
 *
182
 * It is considered that vals[0] represents the value 2 rows above the current,
183
 * while the (locally) previous elements represent the current row. If y < 2,
184
 * then vals[0] should be 0.
185
 * Elements (locally) around vals[prev_row_delta] correspond to the row above
186
 * currnent one.
187
 *
188
 * Values are summed up with the following weights:
189
 *
190
 * 0|0|1|0
191
 * -+-+-+-
192
 * 0|1|2|1
193
 * -+-+-+-
194
 * 1|2|*|
195
 *     ^
196
 *     current position
197
 *
198
 * This method should not be invoked on the 0-th row or 0-th column.
199
 * It is also considered, that there are 2 extra fence columns before the 0-th
200
 * column and 1 fence column to the right of the last column,
201
 * all initialized with zeroes.
202
 */
203
4.30M
inline int WeightedAverageContext(const int* vals, int prev_row_delta) {
204
4.30M
  int sum = 4 + vals[0] + (vals[-kDCTBlockSize] + vals[prev_row_delta]) * 2 +
205
4.30M
            vals[-2 * kDCTBlockSize] + vals[prev_row_delta - kDCTBlockSize] +
206
4.30M
            vals[prev_row_delta + kDCTBlockSize];
207
4.30M
  if ((sum >> (kMaxAverageContext + 2)) != 0) {
208
1.30M
    return kMaxAverageContext;
209
1.30M
  }
210
3.00M
  return Log2FloorNonZero(sum) - 2;
211
4.30M
}
212
213
static const int kACPredictPrecisionBits = 13;
214
static const int kACPredictPrecision = 1 << kACPredictPrecisionBits;
215
216
void ComputeACPredictMultipliers(const int* quant, int* mult_row,
217
                                 int* mult_col);
218
219
// Computes average and sign context from the AC prediction.
220
3.22M
inline void ACPredictContext(int64_t p, size_t* avg_ctx, size_t* sgn) {
221
3.22M
  int multiplier;
222
3.22M
  if (p >= 0) {
223
1.90M
    multiplier = 1;
224
1.90M
  } else {
225
1.31M
    multiplier = -1;
226
1.31M
    p = -p;
227
1.31M
  }
228
3.22M
  size_t ctx;
229
3.22M
  if (p >= (1u << kMaxAverageContext)) {
230
1.86M
    ctx = kMaxAverageContext;
231
1.86M
  } else {
232
    // 0 -> 0, 1 -> 1, 2..3 -> 2, 4..7 -> 3, etc.
233
1.35M
    ctx = Log2FloorNonZero(2 * static_cast<uint32_t>(p)+ 1);
234
1.35M
  }
235
3.22M
  *avg_ctx = ctx;
236
3.22M
  *sgn = kMaxAverageContext + multiplier * ctx;
237
3.22M
}
238
239
inline void ACPredictContextCol(const coeff_t* prev, const coeff_t* cur,
240
1.68M
                                const int* mult, size_t* avg_ctx, size_t* sgn) {
241
1.68M
  coeff_t terms[8];
242
1.68M
  terms[0] = 0;
243
1.68M
  terms[1] = cur[1] + prev[1];
244
1.68M
  terms[2] = cur[2] - prev[2];
245
1.68M
  terms[3] = cur[3] + prev[3];
246
1.68M
  terms[4] = cur[4] - prev[4];
247
1.68M
  terms[5] = cur[5] + prev[5];
248
1.68M
  terms[6] = cur[6] - prev[6];
249
1.68M
  terms[7] = cur[7] + prev[7];
250
1.68M
  int64_t delta = terms[0] * static_cast<int64_t>(mult[0]) +
251
1.68M
                  terms[1] * static_cast<int64_t>(mult[1]) +
252
1.68M
                  terms[2] * static_cast<int64_t>(mult[2]) +
253
1.68M
                  terms[3] * static_cast<int64_t>(mult[3]) +
254
1.68M
                  terms[4] * static_cast<int64_t>(mult[4]) +
255
1.68M
                  terms[5] * static_cast<int64_t>(mult[5]) +
256
1.68M
                  terms[6] * static_cast<int64_t>(mult[6]) +
257
1.68M
                  terms[7] * static_cast<int64_t>(mult[7]);
258
1.68M
  ACPredictContext(prev[0] - delta / kACPredictPrecision, avg_ctx, sgn);
259
1.68M
}
260
261
inline void ACPredictContextRow(const coeff_t* prev, const coeff_t* cur,
262
1.53M
                               const int* mult, size_t* avg_ctx, size_t* sgn) {
263
1.53M
  coeff_t terms[8];
264
1.53M
  terms[0] = 0;
265
1.53M
  terms[1] = cur[8] + prev[8];
266
1.53M
  terms[2] = cur[16] - prev[16];
267
1.53M
  terms[3] = cur[24] + prev[24];
268
1.53M
  terms[4] = cur[32] - prev[32];
269
1.53M
  terms[5] = cur[40] + prev[40];
270
1.53M
  terms[6] = cur[48] - prev[48];
271
1.53M
  terms[7] = cur[56] + prev[56];
272
1.53M
  int64_t delta = terms[0] * static_cast<int64_t>(mult[0]) +
273
1.53M
                  terms[1] * static_cast<int64_t>(mult[1]) +
274
1.53M
                  terms[2] * static_cast<int64_t>(mult[2]) +
275
1.53M
                  terms[3] * static_cast<int64_t>(mult[3]) +
276
1.53M
                  terms[4] * static_cast<int64_t>(mult[4]) +
277
1.53M
                  terms[5] * static_cast<int64_t>(mult[5]) +
278
1.53M
                  terms[6] * static_cast<int64_t>(mult[6]) +
279
1.53M
                  terms[7] * static_cast<int64_t>(mult[7]);
280
1.53M
  ACPredictContext(prev[0] - delta / kACPredictPrecision, avg_ctx, sgn);
281
1.53M
}
282
283
/**
284
 * PRECONDITION: 0 <= prev[i] <= 63
285
 * PRECONDITION: elements of prev at and after x correspond to previous
286
 *               row; elements before x correspond to current row
287
 */
288
3.93M
inline uint8_t NumNonzerosContext(const uint8_t* prev, int x, int y) {
289
3.93M
  size_t prediction;
290
3.93M
  if (y == 0) {
291
275k
    if (x == 0) {
292
      // Special case: top-left block.
293
6.19k
      prediction = 0;
294
268k
    } else {
295
      // No row above; use block at left.
296
268k
      prediction = prev[x - 1];
297
268k
    }
298
3.65M
  } else if (x == 0) {
299
    // No column to the left; use block above.
300
73.0k
    prediction = prev[x];
301
3.58M
  } else {
302
    // Average of left and above blocks.
303
3.58M
    prediction = (prev[x - 1] + prev[x] + 1) / 2;
304
3.58M
  }
305
3.93M
  BRUNSLI_DCHECK(prediction <= kNumNonZeroTreeSize);
306
3.93M
  return static_cast<uint8_t>(prediction / kNumNonZeroQuant);
307
3.93M
}
308
309
// Context for the emptyness of a block is the number of non-empty blocks in the
310
// previous and up neighborhood (blocks beyond the border are assumed
311
// non-empty).
312
static const int kNumIsEmptyBlockContexts = 3;
313
60.3M
inline int IsEmptyBlockContext(const int* prev, int x) {
314
60.3M
  return prev[x - 1] + prev[x];
315
60.3M
}
316
317
// Holds all encoding/decoding state for an image component that is needed to
318
// switch between components during interleaved encoding/decoding.
319
struct ComponentStateDC {
320
  ComponentStateDC()
321
13.1k
      : width(0),
322
13.1k
        is_empty_block_prob(kNumIsEmptyBlockContexts),
323
13.1k
        sign_prob(9),
324
13.1k
        first_extra_bit_prob(10) {
325
13.1k
    InitAll();
326
13.1k
  }
327
328
13.1k
  void SetWidth(int w) {
329
13.1k
    width = w;
330
13.1k
    prev_is_nonempty.resize(w + 1, 1);
331
13.1k
    prev_abs_coeff.resize(w + 3);
332
13.1k
    prev_sign.resize(w + 1);
333
13.1k
  }
334
335
  int width;
336
  Prob is_zero_prob;
337
  std::vector<Prob> is_empty_block_prob;
338
  std::vector<Prob> sign_prob;
339
  std::vector<Prob> first_extra_bit_prob;
340
  std::vector<int> prev_is_nonempty;
341
  std::vector<int> prev_abs_coeff;
342
  std::vector<int> prev_sign;
343
344
 protected:
345
  void InitAll();
346
};
347
348
struct ComponentState {
349
  ComponentState()
350
11.9k
      : width(0),
351
11.9k
        is_zero_prob(kNumNonzeroBuckets * kDCTBlockSize),
352
11.9k
        sign_prob((2 * kMaxAverageContext + 1) * kDCTBlockSize),
353
11.9k
        first_extra_bit_prob(10 * kDCTBlockSize) {
354
11.9k
    InitAll();
355
11.9k
  }
356
357
11.9k
  void SetWidth(int w) {
358
11.9k
    width = w;
359
11.9k
    prev_is_nonempty.resize(w + 1, 1);
360
11.9k
    prev_num_nonzeros.resize(w);
361
11.9k
    prev_abs_coeff.resize(kDCTBlockSize * 2 * (w + 3));
362
11.9k
    prev_sign.resize(kDCTBlockSize * (w + 1));
363
11.9k
  }
364
365
  // Returns the size of the object after constructor and SetWidth(w).
366
  // Used in estimating peak heap memory usage of the brunsli codec.
367
0
  static size_t SizeInBytes(int w) {
368
0
    return (4 + (10 + 3 * w) * kDCTBlockSize + 2 * w) * sizeof(int) +
369
0
           ((kNumNonzeroBuckets + 2 * kMaxAverageContext + 11) * kDCTBlockSize +
370
0
            kNumNonZeroContextCount * kNumNonZeroTreeSize) *
371
0
               sizeof(Prob);
372
0
  }
373
374
  int width;
375
  int context_offset;
376
  uint32_t order[kDCTBlockSize];
377
  int mult_row[kDCTBlockSize];
378
  // mult_col is transposed for more effective ACPredictContextRow execution.
379
  int mult_col[kDCTBlockSize];
380
  std::vector<Prob> is_zero_prob;
381
  std::vector<Prob> sign_prob;
382
  Prob num_nonzero_prob[kNumNonZeroContextCount * kNumNonZeroTreeSize];
383
  std::vector<Prob> first_extra_bit_prob;
384
  std::vector<int> prev_is_nonempty;
385
  std::vector<uint8_t> prev_num_nonzeros;
386
  std::vector<int> prev_abs_coeff;
387
  std::vector<int> prev_sign;
388
389
 protected:
390
  void InitAll();
391
};
392
393
}  // namespace brunsli
394
395
#endif  // BRUNSLI_COMMON_CONTEXT_H_