FFmpeg: libavcodec/rangecoder.h Source File

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rangecoder.h

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1 /*

2 * Range coder

4 *

5 * This file is part of FFmpeg.

6 *

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

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

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

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

11 *

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

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

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

15 * Lesser General Public License for more details.

16 *

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

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

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

20 */

22 /**

23 * @file

24 * Range coder.

25 */

27 #ifndef AVCODEC_RANGECODER_H

28 #define AVCODEC_RANGECODER_H

30 #include <stdint.h>

32 #include "libavutil/common.h"

33 #include "libavutil/avassert.h"

35 typedef struct RangeCoder {

36 int low;

37 int range;

38 int outstanding_count;

39 int outstanding_byte;

40 uint8_t zero_state[256];

41 uint8_t one_state[256];

42 uint8_t *bytestream_start;

43 uint8_t *bytestream;

44 uint8_t *bytestream_end;

45 } RangeCoder;

47 void ff_init_range_encoder(RangeCoder *c, uint8_t *buf, int buf_size);

48 void ff_init_range_decoder(RangeCoder *c, const uint8_t *buf, int buf_size);

49 int ff_rac_terminate(RangeCoder *c);

50 void ff_build_rac_states(RangeCoder *c, int factor, int max_p);

52 static inline void renorm_encoder(RangeCoder *c)

53 {

54 // FIXME: optimize

55 while (c->range < 0x100) {

56 if (c->outstanding_byte < 0) {

57 c->outstanding_byte = c->low >> 8;

58 } else if (c->low <= 0xFF00) {

59 *c->bytestream++ = c->outstanding_byte;

60 for (; c->outstanding_count; c->outstanding_count--)

61 *c->bytestream++ = 0xFF;

62 c->outstanding_byte = c->low >> 8;

63 } else if (c->low >= 0x10000) {

64 *c->bytestream++ = c->outstanding_byte + 1;

65 for (; c->outstanding_count; c->outstanding_count--)

66 *c->bytestream++ = 0x00;

67 c->outstanding_byte = (c->low >> 8) & 0xFF;

68 } else {

69 c->outstanding_count++;

70 }

72 c->low = (c->low & 0xFF) << 8;

73 c->range <<= 8;

74 }

75 }

77 static inline int get_rac_count(RangeCoder *c)

78 {

79 int x = c->bytestream - c->bytestream_start + c->outstanding_count;

80 if (c->outstanding_byte >= 0)

81 x++;

82 return 8 * x - av_log2(c->range);

83 }

85 static inline void put_rac(RangeCoder *c, uint8_t *const state, int bit)

86 {

87 int range1 = (c->range * (*state)) >> 8;

89 av_assert2(*state);

90 av_assert2(range1 < c->range);

91 av_assert2(range1 > 0);

92 if (!bit) {

93 c->range -= range1;

94 *state = c->zero_state[*state];

95 } else {

96 c->low += c->range - range1;

97 c->range = range1;

98 *state = c->one_state[*state];

99 }

100

101 renorm_encoder(c);

102 }

103

104 static inline void refill(RangeCoder *c)

105 {

106 if (c->range < 0x100) {

107 c->range <<= 8;

108 c->low <<= 8;

109 if (c->bytestream < c->bytestream_end)

110 c->low += c->bytestream[0];

111 c->bytestream++;

112 }

113 }

114

115 static inline int get_rac(RangeCoder *c, uint8_t *const state)

116 {

117 int range1 = (c->range * (*state)) >> 8;

118

119 c->range -= range1;

120 #if 1

121 if (c->low < c->range) {

122 *state = c->zero_state[*state];

123 refill(c);

124 return 0;

125 } else {

126 c->low -= c->range;

127 *state = c->one_state[*state];

128 c->range = range1;

129 refill(c);

130 return 1;

131 }

132 #else

133 {

134 int one_mask one_mask = (c->range - c->low - 1) >> 31;

135

136 c->low -= c->range & one_mask;

137 c->range += (range1 - c->range) & one_mask;

138

139 *state = c->zero_state[(*state) + (256 & one_mask)];

140 }

141 refill(c);

142

143 return one_mask & 1;

144 #endif

145 }

146

147 #endif /* AVCODEC_RANGECODER_H */

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