FFmpeg: libavcodec/vpx_rac.h Source File

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vpx_rac.h

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1 /*

3 *

4 * This file is part of FFmpeg.

5 *

6 * FFmpeg is free software; you can redistribute it and/or

7 * modify it under the terms of the GNU Lesser General Public

8 * License as published by the Free Software Foundation; either

9 * version 2.1 of the License, or (at your option) any later version.

10 *

11 * FFmpeg is distributed in the hope that it will be useful,

12 * but WITHOUT ANY WARRANTY; without even the implied warranty of

13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU

14 * Lesser General Public License for more details.

15 *

16 * You should have received a copy of the GNU Lesser General Public

17 * License along with FFmpeg; if not, write to the Free Software

18 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA

19 */

21 /**

22 * @file

23 * Common VP5-VP9 range decoder stuff

24 */

26 #ifndef AVCODEC_VPX_RAC_H

27 #define AVCODEC_VPX_RAC_H

29 #include <stdint.h>

31 #include "config.h"

32 #include "libavutil/attributes.h"

33 #include "bytestream.h"

35 typedef struct VPXRangeCoder {

36 int high;

37 int bits; /* stored negated (i.e. negative "bits" is a positive number of

38 bits left) in order to eliminate a negate in cache refilling */

39 const uint8_t *buffer;

40 const uint8_t *end;

41 unsigned int code_word;

42 int end_reached;

43 } VPXRangeCoder;

45 extern const uint8_t ff_vpx_norm_shift[256];

46 int ff_vpx_init_range_decoder(VPXRangeCoder *c, const uint8_t *buf, int buf_size);

48 /**

49 * returns 1 if the end of the stream has been reached, 0 otherwise.

50 */

51 static av_always_inline int vpx_rac_is_end(VPXRangeCoder *c)

52 {

53 if (c->end <= c->buffer && c->bits >= 0)

54 c->end_reached ++;

55 return c->end_reached > 10;

56 }

58 static av_always_inline unsigned int vpx_rac_renorm(VPXRangeCoder *c)

59 {

60 int shift = ff_vpx_norm_shift[c->high];

61 int bits = c->bits;

62 unsigned int code_word = c->code_word;

64 c->high <<= shift;

65 code_word <<= shift;

66 bits += shift;

67 if(bits >= 0 && c->buffer < c->end) {

68 code_word |= bytestream_get_be16(&c->buffer) << bits;

69 bits -= 16;

70 }

71 c->bits = bits;

72 return code_word;

73 }

75 #if ARCH_ARM

76 #include "arm/vpx_arith.h"

77 #elif ARCH_X86

78 #include "x86/vpx_arith.h"

79 #endif

81 #ifndef vpx_rac_get_prob

82 #define vpx_rac_get_prob vpx_rac_get_prob

83 static av_always_inline int vpx_rac_get_prob(VPXRangeCoder *c, uint8_t prob)

84 {

85 unsigned int code_word = vpx_rac_renorm(c);

86 unsigned int low = 1 + (((c->high - 1) * prob) >> 8);

87 unsigned int low_shift = low << 16;

88 int bit = code_word >= low_shift;

90 c->high = bit ? c->high - low : low;

91 c->code_word = bit ? code_word - low_shift : code_word;

93 return bit;

94 }

95 #endif

97 #ifndef vpx_rac_get_prob_branchy

98 // branchy variant, to be used where there's a branch based on the bit decoded

99 static av_always_inline int vpx_rac_get_prob_branchy(VPXRangeCoder *c, int prob)

100 {

101 unsigned long code_word = vpx_rac_renorm(c);

102 unsigned low = 1 + (((c->high - 1) * prob) >> 8);

103 unsigned low_shift = low << 16;

104

105 if (code_word >= low_shift) {

106 c->high -= low;

107 c->code_word = code_word - low_shift;

108 return 1;

109 }

110

111 c->high = low;

112 c->code_word = code_word;

113 return 0;

114 }

115 #endif

116

117 static av_always_inline int vpx_rac_get(VPXRangeCoder *c)

118 {

119 unsigned int code_word = vpx_rac_renorm(c);

120 /* equiprobable */

121 int low = (c->high + 1) >> 1;

122 unsigned int low_shift = low << 16;

123 int bit = code_word >= low_shift;

124 if (bit) {

125 c->high -= low;

126 code_word -= low_shift;

127 } else {

128 c->high = low;

129 }

130

131 c->code_word = code_word;

132 return bit;

133 }

134

135 #endif /* AVCODEC_VPX_RAC_H */

VPXRangeCoder::end

const uint8_t * end

Definition: vpx_rac.h:40

VPXRangeCoder

Definition: vpx_rac.h:35

bit

#define bit(string, value)

Definition: cbs_mpeg2.c:56

vpx_arith.h

VPXRangeCoder::high

int high

Definition: vpx_rac.h:36

vpx_rac_renorm

static av_always_inline unsigned int vpx_rac_renorm(VPXRangeCoder *c)

Definition: vpx_rac.h:58

bits

uint8_t bits

Definition: vp3data.h:128

VPXRangeCoder::end_reached

int end_reached

Definition: vpx_rac.h:42

ff_vpx_norm_shift

const uint8_t ff_vpx_norm_shift[256]

Definition: vpx_rac.c:27

Undefined Behavior In the C some operations are like signed integer dereferencing freed accessing outside allocated Undefined Behavior must not occur in a C it is not safe even if the output of undefined operations is unused The unsafety may seem nit picking but Optimizing compilers have in fact optimized code on the assumption that no undefined Behavior occurs Optimizing code based on wrong assumptions can and has in some cases lead to effects beyond the output of computations The signed integer overflow problem in speed critical code Code which is highly optimized and works with signed integers sometimes has the problem that often the output of the computation does not c

Definition: undefined.txt:32

vpx_arith.h

VPXRangeCoder::buffer

const uint8_t * buffer

Definition: vpx_rac.h:39

shift

static int shift(int a, int b)

Definition: bonk.c:261

attributes.h

vpx_rac_is_end

static av_always_inline int vpx_rac_is_end(VPXRangeCoder *c)

returns 1 if the end of the stream has been reached, 0 otherwise.