/src/libwebp/src/utils/random_utils.h

Source (jump to first uncovered line)
// Copyright 2013 Google Inc. All Rights Reserved.
//
// Use of this source code is governed by a BSD-style license
// that can be found in the COPYING file in the root of the source
// tree. An additional intellectual property rights grant can be found
// in the file PATENTS. All contributing project authors may
// be found in the AUTHORS file in the root of the source tree.
// -----------------------------------------------------------------------------
//
// Pseudo-random utilities
//
// Author: Skal (pascal.massimino@gmail.com)

#ifndef WEBP_UTILS_RANDOM_UTILS_H_
#define WEBP_UTILS_RANDOM_UTILS_H_

#include <assert.h>
#include "src/webp/types.h"

#ifdef __cplusplus
extern "C" {
#endif

#define VP8_RANDOM_DITHER_FIX 8   // fixed-point precision for dithering
#define VP8_RANDOM_TABLE_SIZE 55

typedef struct {
  int index1_, index2_;
  uint32_t tab_[VP8_RANDOM_TABLE_SIZE];
  int amp_;
} VP8Random;

// Initializes random generator with an amplitude 'dithering' in range [0..1].
void VP8InitRandom(VP8Random* const rg, float dithering);

// Returns a centered pseudo-random number with 'num_bits' amplitude.
// (uses D.Knuth's Difference-based random generator).
// 'amp' is in VP8_RANDOM_DITHER_FIX fixed-point precision.
static WEBP_INLINE int VP8RandomBits2(VP8Random* const rg, int num_bits,
                                      int amp) {
  int diff;
  assert(num_bits + VP8_RANDOM_DITHER_FIX <= 31);
  diff = rg->tab_[rg->index1_] - rg->tab_[rg->index2_];
  if (diff < 0) diff += (1u << 31);
  rg->tab_[rg->index1_] = diff;
  if (++rg->index1_ == VP8_RANDOM_TABLE_SIZE) rg->index1_ = 0;
  if (++rg->index2_ == VP8_RANDOM_TABLE_SIZE) rg->index2_ = 0;
  // sign-extend, 0-center
  diff = (int)((uint32_t)diff << 1) >> (32 - num_bits);
  diff = (diff * amp) >> VP8_RANDOM_DITHER_FIX;  // restrict range
  diff += 1 << (num_bits - 1);                   // shift back to 0.5-center
  return diff;
}

static WEBP_INLINE int VP8RandomBits(VP8Random* const rg, int num_bits) {
  return VP8RandomBits2(rg, num_bits, rg->amp_);
}

#ifdef __cplusplus
}    // extern "C"
#endif

#endif  // WEBP_UTILS_RANDOM_UTILS_H_

Coverage Report

Created: 2024-07-27 06:27

Line	Count	Source (jump to first uncovered line)
1		// Copyright 2013 Google Inc. All Rights Reserved.
2		//
3		// Use of this source code is governed by a BSD-style license
4		// that can be found in the COPYING file in the root of the source
5		// tree. An additional intellectual property rights grant can be found
6		// in the file PATENTS. All contributing project authors may
7		// be found in the AUTHORS file in the root of the source tree.
8		// -----------------------------------------------------------------------------
9		//
10		// Pseudo-random utilities
11		//
12		// Author: Skal (pascal.massimino@gmail.com)
13
14		#ifndef WEBP_UTILS_RANDOM_UTILS_H_
15		#define WEBP_UTILS_RANDOM_UTILS_H_
16
17		#include <assert.h>
18		#include "src/webp/types.h"
19
20		#ifdef __cplusplus
21		extern "C" {
22		#endif
23
24	0	#define VP8_RANDOM_DITHER_FIX 8 // fixed-point precision for dithering
25	0	#define VP8_RANDOM_TABLE_SIZE 55
26
27		typedef struct {
28		int index1_, index2_;
29		uint32_t tab_[VP8_RANDOM_TABLE_SIZE];
30		int amp_;
31		} VP8Random;
32
33		// Initializes random generator with an amplitude 'dithering' in range [0..1].
34		void VP8InitRandom(VP8Random* const rg, float dithering);
35
36		// Returns a centered pseudo-random number with 'num_bits' amplitude.
37		// (uses D.Knuth's Difference-based random generator).
38		// 'amp' is in VP8_RANDOM_DITHER_FIX fixed-point precision.
39		static WEBP_INLINE int VP8RandomBits2(VP8Random* const rg, int num_bits,
40	0	int amp) {
41	0	int diff;
42	0	assert(num_bits + VP8_RANDOM_DITHER_FIX <= 31);
43	0	diff = rg->tab_[rg->index1_] - rg->tab_[rg->index2_];
44	0	if (diff < 0) diff += (1u << 31);
45	0	rg->tab_[rg->index1_] = diff;
46	0	if (++rg->index1_ == VP8_RANDOM_TABLE_SIZE) rg->index1_ = 0;
47	0	if (++rg->index2_ == VP8_RANDOM_TABLE_SIZE) rg->index2_ = 0;
48		// sign-extend, 0-center
49	0	diff = (int)((uint32_t)diff << 1) >> (32 - num_bits);
50	0	diff = (diff * amp) >> VP8_RANDOM_DITHER_FIX; // restrict range
51	0	diff += 1 << (num_bits - 1); // shift back to 0.5-center
52	0	return diff;
53	0	} Unexecuted instantiation: webp_dec.c:VP8RandomBits2 Unexecuted instantiation: buffer_dec.c:VP8RandomBits2 Unexecuted instantiation: frame_dec.c:VP8RandomBits2 Unexecuted instantiation: io_dec.c:VP8RandomBits2 Unexecuted instantiation: vp8_dec.c:VP8RandomBits2 Unexecuted instantiation: dec.c:VP8RandomBits2 Unexecuted instantiation: dec_sse2.c:VP8RandomBits2 Unexecuted instantiation: dec_sse41.c:VP8RandomBits2 Unexecuted instantiation: picture_csp_enc.c:VP8RandomBits2 Unexecuted instantiation: random_utils.c:VP8RandomBits2 Unexecuted instantiation: alpha_dec.c:VP8RandomBits2 Unexecuted instantiation: quant_dec.c:VP8RandomBits2 Unexecuted instantiation: tree_dec.c:VP8RandomBits2
54
55	0	static WEBP_INLINE int VP8RandomBits(VP8Random* const rg, int num_bits) {
56	0	return VP8RandomBits2(rg, num_bits, rg->amp_);
57	0	} Unexecuted instantiation: webp_dec.c:VP8RandomBits Unexecuted instantiation: buffer_dec.c:VP8RandomBits Unexecuted instantiation: frame_dec.c:VP8RandomBits Unexecuted instantiation: io_dec.c:VP8RandomBits Unexecuted instantiation: vp8_dec.c:VP8RandomBits Unexecuted instantiation: dec.c:VP8RandomBits Unexecuted instantiation: dec_sse2.c:VP8RandomBits Unexecuted instantiation: dec_sse41.c:VP8RandomBits Unexecuted instantiation: picture_csp_enc.c:VP8RandomBits Unexecuted instantiation: random_utils.c:VP8RandomBits Unexecuted instantiation: alpha_dec.c:VP8RandomBits Unexecuted instantiation: quant_dec.c:VP8RandomBits Unexecuted instantiation: tree_dec.c:VP8RandomBits
58
59		#ifdef __cplusplus
60		} // extern "C"
61		#endif
62
63		#endif // WEBP_UTILS_RANDOM_UTILS_H_