1 /* 2 * Mu-Law conversion Plug-In Interface 3 * Copyright (c) 1999 by Jaroslav Kysela <perex@perex.cz> 4 * Uros Bizjak <uros@kss-loka.si> 5 * 6 * Based on reference implementation by Sun Microsystems, Inc. 7 * 8 * This library is free software; you can redistribute it and/or modify 9 * it under the terms of the GNU Library General Public License as 10 * published by the Free Software Foundation; either version 2 of 11 * the License, or (at your option) any later version. 12 * 13 * This program 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 16 * GNU Library General Public License for more details. 17 * 18 * You should have received a copy of the GNU Library General Public 19 * License along with this library; if not, write to the Free Software 20 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA 21 * 22 */ 23 24 #include <linux/time.h> 25 #include <sound/core.h> 26 #include <sound/pcm.h> 27 #include "pcm_plugin.h" 28 29 #define SIGN_BIT (0x80) /* Sign bit for a u-law byte. */ 30 #define QUANT_MASK (0xf) /* Quantization field mask. */ 31 #define NSEGS (8) /* Number of u-law segments. */ 32 #define SEG_SHIFT (4) /* Left shift for segment number. */ 33 #define SEG_MASK (0x70) /* Segment field mask. */ 34 35 static inline int val_seg(int val) 36 { 37 int r = 0; 38 val >>= 7; 39 if (val & 0xf0) { 40 val >>= 4; 41 r += 4; 42 } 43 if (val & 0x0c) { 44 val >>= 2; 45 r += 2; 46 } 47 if (val & 0x02) 48 r += 1; 49 return r; 50 } 51 52 #define BIAS (0x84) /* Bias for linear code. */ 53 54 /* 55 * linear2ulaw() - Convert a linear PCM value to u-law 56 * 57 * In order to simplify the encoding process, the original linear magnitude 58 * is biased by adding 33 which shifts the encoding range from (0 - 8158) to 59 * (33 - 8191). The result can be seen in the following encoding table: 60 * 61 * Biased Linear Input Code Compressed Code 62 * ------------------------ --------------- 63 * 00000001wxyza 000wxyz 64 * 0000001wxyzab 001wxyz 65 * 000001wxyzabc 010wxyz 66 * 00001wxyzabcd 011wxyz 67 * 0001wxyzabcde 100wxyz 68 * 001wxyzabcdef 101wxyz 69 * 01wxyzabcdefg 110wxyz 70 * 1wxyzabcdefgh 111wxyz 71 * 72 * Each biased linear code has a leading 1 which identifies the segment 73 * number. The value of the segment number is equal to 7 minus the number 74 * of leading 0's. The quantization interval is directly available as the 75 * four bits wxyz. * The trailing bits (a - h) are ignored. 76 * 77 * Ordinarily the complement of the resulting code word is used for 78 * transmission, and so the code word is complemented before it is returned. 79 * 80 * For further information see John C. Bellamy's Digital Telephony, 1982, 81 * John Wiley & Sons, pps 98-111 and 472-476. 82 */ 83 static unsigned char linear2ulaw(int pcm_val) /* 2's complement (16-bit range) */ 84 { 85 int mask; 86 int seg; 87 unsigned char uval; 88 89 /* Get the sign and the magnitude of the value. */ 90 if (pcm_val < 0) { 91 pcm_val = BIAS - pcm_val; 92 mask = 0x7F; 93 } else { 94 pcm_val += BIAS; 95 mask = 0xFF; 96 } 97 if (pcm_val > 0x7FFF) 98 pcm_val = 0x7FFF; 99 100 /* Convert the scaled magnitude to segment number. */ 101 seg = val_seg(pcm_val); 102 103 /* 104 * Combine the sign, segment, quantization bits; 105 * and complement the code word. 106 */ 107 uval = (seg << 4) | ((pcm_val >> (seg + 3)) & 0xF); 108 return uval ^ mask; 109 } 110 111 /* 112 * ulaw2linear() - Convert a u-law value to 16-bit linear PCM 113 * 114 * First, a biased linear code is derived from the code word. An unbiased 115 * output can then be obtained by subtracting 33 from the biased code. 116 * 117 * Note that this function expects to be passed the complement of the 118 * original code word. This is in keeping with ISDN conventions. 119 */ 120 static int ulaw2linear(unsigned char u_val) 121 { 122 int t; 123 124 /* Complement to obtain normal u-law value. */ 125 u_val = ~u_val; 126 127 /* 128 * Extract and bias the quantization bits. Then 129 * shift up by the segment number and subtract out the bias. 130 */ 131 t = ((u_val & QUANT_MASK) << 3) + BIAS; 132 t <<= ((unsigned)u_val & SEG_MASK) >> SEG_SHIFT; 133 134 return ((u_val & SIGN_BIT) ? (BIAS - t) : (t - BIAS)); 135 } 136 137 /* 138 * Basic Mu-Law plugin 139 */ 140 141 typedef void (*mulaw_f)(struct snd_pcm_plugin *plugin, 142 const struct snd_pcm_plugin_channel *src_channels, 143 struct snd_pcm_plugin_channel *dst_channels, 144 snd_pcm_uframes_t frames); 145 146 struct mulaw_priv { 147 mulaw_f func; 148 int cvt_endian; /* need endian conversion? */ 149 unsigned int native_ofs; /* byte offset in native format */ 150 unsigned int copy_ofs; /* byte offset in s16 format */ 151 unsigned int native_bytes; /* byte size of the native format */ 152 unsigned int copy_bytes; /* bytes to copy per conversion */ 153 u16 flip; /* MSB flip for signedness, done after endian conversion */ 154 }; 155 156 static inline void cvt_s16_to_native(struct mulaw_priv *data, 157 unsigned char *dst, u16 sample) 158 { 159 sample ^= data->flip; 160 if (data->cvt_endian) 161 sample = swab16(sample); 162 if (data->native_bytes > data->copy_bytes) 163 memset(dst, 0, data->native_bytes); 164 memcpy(dst + data->native_ofs, (char *)&sample + data->copy_ofs, 165 data->copy_bytes); 166 } 167 168 static void mulaw_decode(struct snd_pcm_plugin *plugin, 169 const struct snd_pcm_plugin_channel *src_channels, 170 struct snd_pcm_plugin_channel *dst_channels, 171 snd_pcm_uframes_t frames) 172 { 173 struct mulaw_priv *data = (struct mulaw_priv *)plugin->extra_data; 174 int channel; 175 int nchannels = plugin->src_format.channels; 176 for (channel = 0; channel < nchannels; ++channel) { 177 char *src; 178 char *dst; 179 int src_step, dst_step; 180 snd_pcm_uframes_t frames1; 181 if (!src_channels[channel].enabled) { 182 if (dst_channels[channel].wanted) 183 snd_pcm_area_silence(&dst_channels[channel].area, 0, frames, plugin->dst_format.format); 184 dst_channels[channel].enabled = 0; 185 continue; 186 } 187 dst_channels[channel].enabled = 1; 188 src = src_channels[channel].area.addr + src_channels[channel].area.first / 8; 189 dst = dst_channels[channel].area.addr + dst_channels[channel].area.first / 8; 190 src_step = src_channels[channel].area.step / 8; 191 dst_step = dst_channels[channel].area.step / 8; 192 frames1 = frames; 193 while (frames1-- > 0) { 194 signed short sample = ulaw2linear(*src); 195 cvt_s16_to_native(data, dst, sample); 196 src += src_step; 197 dst += dst_step; 198 } 199 } 200 } 201 202 static inline signed short cvt_native_to_s16(struct mulaw_priv *data, 203 unsigned char *src) 204 { 205 u16 sample = 0; 206 memcpy((char *)&sample + data->copy_ofs, src + data->native_ofs, 207 data->copy_bytes); 208 if (data->cvt_endian) 209 sample = swab16(sample); 210 sample ^= data->flip; 211 return (signed short)sample; 212 } 213 214 static void mulaw_encode(struct snd_pcm_plugin *plugin, 215 const struct snd_pcm_plugin_channel *src_channels, 216 struct snd_pcm_plugin_channel *dst_channels, 217 snd_pcm_uframes_t frames) 218 { 219 struct mulaw_priv *data = (struct mulaw_priv *)plugin->extra_data; 220 int channel; 221 int nchannels = plugin->src_format.channels; 222 for (channel = 0; channel < nchannels; ++channel) { 223 char *src; 224 char *dst; 225 int src_step, dst_step; 226 snd_pcm_uframes_t frames1; 227 if (!src_channels[channel].enabled) { 228 if (dst_channels[channel].wanted) 229 snd_pcm_area_silence(&dst_channels[channel].area, 0, frames, plugin->dst_format.format); 230 dst_channels[channel].enabled = 0; 231 continue; 232 } 233 dst_channels[channel].enabled = 1; 234 src = src_channels[channel].area.addr + src_channels[channel].area.first / 8; 235 dst = dst_channels[channel].area.addr + dst_channels[channel].area.first / 8; 236 src_step = src_channels[channel].area.step / 8; 237 dst_step = dst_channels[channel].area.step / 8; 238 frames1 = frames; 239 while (frames1-- > 0) { 240 signed short sample = cvt_native_to_s16(data, src); 241 *dst = linear2ulaw(sample); 242 src += src_step; 243 dst += dst_step; 244 } 245 } 246 } 247 248 static snd_pcm_sframes_t mulaw_transfer(struct snd_pcm_plugin *plugin, 249 const struct snd_pcm_plugin_channel *src_channels, 250 struct snd_pcm_plugin_channel *dst_channels, 251 snd_pcm_uframes_t frames) 252 { 253 struct mulaw_priv *data; 254 255 if (snd_BUG_ON(!plugin || !src_channels || !dst_channels)) 256 return -ENXIO; 257 if (frames == 0) 258 return 0; 259 #ifdef CONFIG_SND_DEBUG 260 { 261 unsigned int channel; 262 for (channel = 0; channel < plugin->src_format.channels; channel++) { 263 if (snd_BUG_ON(src_channels[channel].area.first % 8 || 264 src_channels[channel].area.step % 8)) 265 return -ENXIO; 266 if (snd_BUG_ON(dst_channels[channel].area.first % 8 || 267 dst_channels[channel].area.step % 8)) 268 return -ENXIO; 269 } 270 } 271 #endif 272 if (frames > dst_channels[0].frames) 273 frames = dst_channels[0].frames; 274 data = (struct mulaw_priv *)plugin->extra_data; 275 data->func(plugin, src_channels, dst_channels, frames); 276 return frames; 277 } 278 279 static void init_data(struct mulaw_priv *data, snd_pcm_format_t format) 280 { 281 #ifdef SNDRV_LITTLE_ENDIAN 282 data->cvt_endian = snd_pcm_format_big_endian(format) > 0; 283 #else 284 data->cvt_endian = snd_pcm_format_little_endian(format) > 0; 285 #endif 286 if (!snd_pcm_format_signed(format)) 287 data->flip = 0x8000; 288 data->native_bytes = snd_pcm_format_physical_width(format) / 8; 289 data->copy_bytes = data->native_bytes < 2 ? 1 : 2; 290 if (snd_pcm_format_little_endian(format)) { 291 data->native_ofs = data->native_bytes - data->copy_bytes; 292 data->copy_ofs = 2 - data->copy_bytes; 293 } else { 294 /* S24 in 4bytes need an 1 byte offset */ 295 data->native_ofs = data->native_bytes - 296 snd_pcm_format_width(format) / 8; 297 } 298 } 299 300 int snd_pcm_plugin_build_mulaw(struct snd_pcm_substream *plug, 301 struct snd_pcm_plugin_format *src_format, 302 struct snd_pcm_plugin_format *dst_format, 303 struct snd_pcm_plugin **r_plugin) 304 { 305 int err; 306 struct mulaw_priv *data; 307 struct snd_pcm_plugin *plugin; 308 struct snd_pcm_plugin_format *format; 309 mulaw_f func; 310 311 if (snd_BUG_ON(!r_plugin)) 312 return -ENXIO; 313 *r_plugin = NULL; 314 315 if (snd_BUG_ON(src_format->rate != dst_format->rate)) 316 return -ENXIO; 317 if (snd_BUG_ON(src_format->channels != dst_format->channels)) 318 return -ENXIO; 319 320 if (dst_format->format == SNDRV_PCM_FORMAT_MU_LAW) { 321 format = src_format; 322 func = mulaw_encode; 323 } 324 else if (src_format->format == SNDRV_PCM_FORMAT_MU_LAW) { 325 format = dst_format; 326 func = mulaw_decode; 327 } 328 else { 329 snd_BUG(); 330 return -EINVAL; 331 } 332 if (!snd_pcm_format_linear(format->format)) 333 return -EINVAL; 334 335 err = snd_pcm_plugin_build(plug, "Mu-Law<->linear conversion", 336 src_format, dst_format, 337 sizeof(struct mulaw_priv), &plugin); 338 if (err < 0) 339 return err; 340 data = (struct mulaw_priv *)plugin->extra_data; 341 data->func = func; 342 init_data(data, format->format); 343 plugin->transfer = mulaw_transfer; 344 *r_plugin = plugin; 345 return 0; 346 } 347