FFmpeg: libavcodec/lzw.c Source File

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libavcodec

lzw.c

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1 /*

2 * LZW decoder

5 *

6 * This file is part of FFmpeg.

7 *

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

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

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

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

12 *

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

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

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

16 * Lesser General Public License for more details.

17 *

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

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

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

21 */

23 /**

24 * @file

25 * @brief LZW decoding routines

26 * @author Fabrice Bellard

27 * @author modified for use in TIFF by Konstantin Shishkov

28 */

30 #include "avcodec.h"

31 #include "bytestream.h"

32 #include "lzw.h"

33 #include "libavutil/mem.h"

35 #define LZW_MAXBITS 12

36 #define LZW_SIZTABLE (1<<LZW_MAXBITS)

38 static const uint16_t mask[17] =

39 {

40 0x0000, 0x0001, 0x0003, 0x0007,

41 0x000F, 0x001F, 0x003F, 0x007F,

42 0x00FF, 0x01FF, 0x03FF, 0x07FF,

43 0x0FFF, 0x1FFF, 0x3FFF, 0x7FFF, 0xFFFF

44 };

46 struct LZWState {

47 GetByteContext gb;

48 int bbits;

49 unsigned int bbuf;

51 int mode; ///< Decoder mode

52 int cursize; ///< The current code size

53 int curmask;

54 int codesize;

55 int clear_code;

56 int end_code;

57 int newcodes; ///< First available code

58 int top_slot; ///< Highest code for current size

59 int extra_slot;

60 int slot; ///< Last read code

61 int fc, oc;

62 uint8_t *sp;

63 uint8_t stack[LZW_SIZTABLE];

64 uint8_t suffix[LZW_SIZTABLE];

65 uint16_t prefix[LZW_SIZTABLE];

66 int bs; ///< current buffer size for GIF

67 };

69 /* get one code from stream */

70 static int lzw_get_code(struct LZWState * s)

71 {

72 int c;

74 if(s->mode == FF_LZW_GIF) {

75 while (s->bbits < s->cursize) {

76 if (!s->bs) {

77 s->bs = bytestream2_get_byte(&s->gb);

78 }

79 s->bbuf |= bytestream2_get_byte(&s->gb) << s->bbits;

80 s->bbits += 8;

81 s->bs--;

82 }

83 c = s->bbuf;

84 s->bbuf >>= s->cursize;

85 } else { // TIFF

86 while (s->bbits < s->cursize) {

87 s->bbuf = (s->bbuf << 8) | bytestream2_get_byte(&s->gb);

88 s->bbits += 8;

89 }

90 c = s->bbuf >> (s->bbits - s->cursize);

91 }

92 s->bbits -= s->cursize;

93 return c & s->curmask;

94 }

96 void ff_lzw_decode_tail(LZWState *p)

97 {

98 struct LZWState *s = (struct LZWState *)p;

100 if(s->mode == FF_LZW_GIF) {

101 while (s->bs > 0 && bytestream2_get_bytes_left(&s->gb)) {

102 bytestream2_skip(&s->gb, s->bs);

103 s->bs = bytestream2_get_byte(&s->gb);

104 }

105 }else

106 bytestream2_skip(&s->gb, bytestream2_get_bytes_left(&s->gb));

107 }

108

109 av_cold void ff_lzw_decode_open(LZWState **p)

110 {

111 *p = av_mallocz(sizeof(struct LZWState));

112 }

113

114 av_cold void ff_lzw_decode_close(LZWState **p)

115 {

116 av_freep(p);

117 }

118

119 /**

120 * Initialize LZW decoder

121 * @param p LZW context

122 * @param csize initial code size in bits

123 * @param buf input data

124 * @param buf_size input data size

125 * @param mode decoder working mode - either GIF or TIFF

126 */

127 int ff_lzw_decode_init(LZWState *p, int csize, const uint8_t *buf, int buf_size, int mode)

128 {

129 struct LZWState *s = (struct LZWState *)p;

130

131 if(csize < 1 || csize >= LZW_MAXBITS)

132 return -1;

133 /* read buffer */

134 bytestream2_init(&s->gb, buf, buf_size);

135 s->bbuf = 0;

136 s->bbits = 0;

137 s->bs = 0;

138

139 /* decoder */

140 s->codesize = csize;

141 s->cursize = s->codesize + 1;

142 s->curmask = mask[s->cursize];

143 s->top_slot = 1 << s->cursize;

144 s->clear_code = 1 << s->codesize;

145 s->end_code = s->clear_code + 1;

146 s->slot = s->newcodes = s->clear_code + 2;

147 s->oc = s->fc = -1;

148 s->sp = s->stack;

149

150 s->mode = mode;

151 s->extra_slot = s->mode == FF_LZW_TIFF;

152 return 0;

153 }

154

155 /**

156 * Decode given number of bytes

157 * NOTE: the algorithm here is inspired from the LZW GIF decoder

158 * written by Steven A. Bennett in 1987.

159 *

160 * @param p LZW context

161 * @param buf output buffer

162 * @param len number of bytes to decode

163 * @return number of bytes decoded

164 */

165 int ff_lzw_decode(LZWState *p, uint8_t *buf, int len){

166 int l, c, code, oc, fc;

167 uint8_t *sp;

168 struct LZWState *s = (struct LZWState *)p;

169

170 if (s->end_code < 0)

171 return 0;

172

173 l = len;

174 sp = s->sp;

175 oc = s->oc;

176 fc = s->fc;

177

178 for (;;) {

179 while (sp > s->stack) {

180 *buf++ = *(--sp);

181 if ((--l) == 0)

182 goto the_end;

183 }

184 c = lzw_get_code(s);

185 if (c == s->end_code) {

186 break;

187 } else if (c == s->clear_code) {

188 s->cursize = s->codesize + 1;

189 s->curmask = mask[s->cursize];

190 s->slot = s->newcodes;

191 s->top_slot = 1 << s->cursize;

192 fc= oc= -1;

193 } else {

194 code = c;

195 if (code == s->slot && fc>=0) {

196 *sp++ = fc;

197 code = oc;

198 }else if(code >= s->slot)

199 break;

200 while (code >= s->newcodes) {

201 *sp++ = s->suffix[code];

202 code = s->prefix[code];

203 }

204 *sp++ = code;

205 if (s->slot < s->top_slot && oc>=0) {

206 s->suffix[s->slot] = code;

207 s->prefix[s->slot++] = oc;

208 }

209 fc = code;

210 oc = c;

211 if (s->slot >= s->top_slot - s->extra_slot) {

212 if (s->cursize < LZW_MAXBITS) {

213 s->top_slot <<= 1;

214 s->curmask = mask[++s->cursize];

215 }

216 }

217 }

218 }

219 s->end_code = -1;

220 the_end:

221 s->sp = sp;

222 s->oc = oc;

223 s->fc = fc;

224 return len - l;

225 }

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