1 /* 2 * Mu-Law conversion Plug-In Interface 3 * Copyright (c) 1999 by Jaroslav Kysela <perex@suse.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 <sound/driver.h> 25 26 #ifdef CONFIG_SND_PCM_OSS_PLUGINS 27 28 #include <linux/time.h> 29 #include <sound/core.h> 30 #include <sound/pcm.h> 31 #include "pcm_plugin.h" 32 33 #define SIGN_BIT (0x80) /* Sign bit for a u-law byte. */ 34 #define QUANT_MASK (0xf) /* Quantization field mask. */ 35 #define NSEGS (8) /* Number of u-law segments. */ 36 #define SEG_SHIFT (4) /* Left shift for segment number. */ 37 #define SEG_MASK (0x70) /* Segment field mask. */ 38 39 static inline int val_seg(int val) 40 { 41 int r = 0; 42 val >>= 7; 43 if (val & 0xf0) { 44 val >>= 4; 45 r += 4; 46 } 47 if (val & 0x0c) { 48 val >>= 2; 49 r += 2; 50 } 51 if (val & 0x02) 52 r += 1; 53 return r; 54 } 55 56 #define BIAS (0x84) /* Bias for linear code. */ 57 58 /* 59 * linear2ulaw() - Convert a linear PCM value to u-law 60 * 61 * In order to simplify the encoding process, the original linear magnitude 62 * is biased by adding 33 which shifts the encoding range from (0 - 8158) to 63 * (33 - 8191). The result can be seen in the following encoding table: 64 * 65 * Biased Linear Input Code Compressed Code 66 * ------------------------ --------------- 67 * 00000001wxyza 000wxyz 68 * 0000001wxyzab 001wxyz 69 * 000001wxyzabc 010wxyz 70 * 00001wxyzabcd 011wxyz 71 * 0001wxyzabcde 100wxyz 72 * 001wxyzabcdef 101wxyz 73 * 01wxyzabcdefg 110wxyz 74 * 1wxyzabcdefgh 111wxyz 75 * 76 * Each biased linear code has a leading 1 which identifies the segment 77 * number. The value of the segment number is equal to 7 minus the number 78 * of leading 0's. The quantization interval is directly available as the 79 * four bits wxyz. * The trailing bits (a - h) are ignored. 80 * 81 * Ordinarily the complement of the resulting code word is used for 82 * transmission, and so the code word is complemented before it is returned. 83 * 84 * For further information see John C. Bellamy's Digital Telephony, 1982, 85 * John Wiley & Sons, pps 98-111 and 472-476. 86 */ 87 static unsigned char linear2ulaw(int pcm_val) /* 2's complement (16-bit range) */ 88 { 89 int mask; 90 int seg; 91 unsigned char uval; 92 93 /* Get the sign and the magnitude of the value. */ 94 if (pcm_val < 0) { 95 pcm_val = BIAS - pcm_val; 96 mask = 0x7F; 97 } else { 98 pcm_val += BIAS; 99 mask = 0xFF; 100 } 101 if (pcm_val > 0x7FFF) 102 pcm_val = 0x7FFF; 103 104 /* Convert the scaled magnitude to segment number. */ 105 seg = val_seg(pcm_val); 106 107 /* 108 * Combine the sign, segment, quantization bits; 109 * and complement the code word. 110 */ 111 uval = (seg << 4) | ((pcm_val >> (seg + 3)) & 0xF); 112 return uval ^ mask; 113 } 114 115 /* 116 * ulaw2linear() - Convert a u-law value to 16-bit linear PCM 117 * 118 * First, a biased linear code is derived from the code word. An unbiased 119 * output can then be obtained by subtracting 33 from the biased code. 120 * 121 * Note that this function expects to be passed the complement of the 122 * original code word. This is in keeping with ISDN conventions. 123 */ 124 static int ulaw2linear(unsigned char u_val) 125 { 126 int t; 127 128 /* Complement to obtain normal u-law value. */ 129 u_val = ~u_val; 130 131 /* 132 * Extract and bias the quantization bits. Then 133 * shift up by the segment number and subtract out the bias. 134 */ 135 t = ((u_val & QUANT_MASK) << 3) + BIAS; 136 t <<= ((unsigned)u_val & SEG_MASK) >> SEG_SHIFT; 137 138 return ((u_val & SIGN_BIT) ? (BIAS - t) : (t - BIAS)); 139 } 140 141 /* 142 * Basic Mu-Law plugin 143 */ 144 145 typedef void (*mulaw_f)(struct snd_pcm_plugin *plugin, 146 const struct snd_pcm_plugin_channel *src_channels, 147 struct snd_pcm_plugin_channel *dst_channels, 148 snd_pcm_uframes_t frames); 149 150 struct mulaw_priv { 151 mulaw_f func; 152 int conv; 153 }; 154 155 static void mulaw_decode(struct snd_pcm_plugin *plugin, 156 const struct snd_pcm_plugin_channel *src_channels, 157 struct snd_pcm_plugin_channel *dst_channels, 158 snd_pcm_uframes_t frames) 159 { 160 #define PUT_S16_LABELS 161 #include "plugin_ops.h" 162 #undef PUT_S16_LABELS 163 struct mulaw_priv *data = (struct mulaw_priv *)plugin->extra_data; 164 void *put = put_s16_labels[data->conv]; 165 int channel; 166 int nchannels = plugin->src_format.channels; 167 for (channel = 0; channel < nchannels; ++channel) { 168 char *src; 169 char *dst; 170 int src_step, dst_step; 171 snd_pcm_uframes_t frames1; 172 if (!src_channels[channel].enabled) { 173 if (dst_channels[channel].wanted) 174 snd_pcm_area_silence(&dst_channels[channel].area, 0, frames, plugin->dst_format.format); 175 dst_channels[channel].enabled = 0; 176 continue; 177 } 178 dst_channels[channel].enabled = 1; 179 src = src_channels[channel].area.addr + src_channels[channel].area.first / 8; 180 dst = dst_channels[channel].area.addr + dst_channels[channel].area.first / 8; 181 src_step = src_channels[channel].area.step / 8; 182 dst_step = dst_channels[channel].area.step / 8; 183 frames1 = frames; 184 while (frames1-- > 0) { 185 signed short sample = ulaw2linear(*src); 186 goto *put; 187 #define PUT_S16_END after 188 #include "plugin_ops.h" 189 #undef PUT_S16_END 190 after: 191 src += src_step; 192 dst += dst_step; 193 } 194 } 195 } 196 197 static void mulaw_encode(struct snd_pcm_plugin *plugin, 198 const struct snd_pcm_plugin_channel *src_channels, 199 struct snd_pcm_plugin_channel *dst_channels, 200 snd_pcm_uframes_t frames) 201 { 202 #define GET_S16_LABELS 203 #include "plugin_ops.h" 204 #undef GET_S16_LABELS 205 struct mulaw_priv *data = (struct mulaw_priv *)plugin->extra_data; 206 void *get = get_s16_labels[data->conv]; 207 int channel; 208 int nchannels = plugin->src_format.channels; 209 signed short sample = 0; 210 for (channel = 0; channel < nchannels; ++channel) { 211 char *src; 212 char *dst; 213 int src_step, dst_step; 214 snd_pcm_uframes_t frames1; 215 if (!src_channels[channel].enabled) { 216 if (dst_channels[channel].wanted) 217 snd_pcm_area_silence(&dst_channels[channel].area, 0, frames, plugin->dst_format.format); 218 dst_channels[channel].enabled = 0; 219 continue; 220 } 221 dst_channels[channel].enabled = 1; 222 src = src_channels[channel].area.addr + src_channels[channel].area.first / 8; 223 dst = dst_channels[channel].area.addr + dst_channels[channel].area.first / 8; 224 src_step = src_channels[channel].area.step / 8; 225 dst_step = dst_channels[channel].area.step / 8; 226 frames1 = frames; 227 while (frames1-- > 0) { 228 goto *get; 229 #define GET_S16_END after 230 #include "plugin_ops.h" 231 #undef GET_S16_END 232 after: 233 *dst = linear2ulaw(sample); 234 src += src_step; 235 dst += dst_step; 236 } 237 } 238 } 239 240 static snd_pcm_sframes_t mulaw_transfer(struct snd_pcm_plugin *plugin, 241 const struct snd_pcm_plugin_channel *src_channels, 242 struct snd_pcm_plugin_channel *dst_channels, 243 snd_pcm_uframes_t frames) 244 { 245 struct mulaw_priv *data; 246 247 snd_assert(plugin != NULL && src_channels != NULL && dst_channels != NULL, return -ENXIO); 248 if (frames == 0) 249 return 0; 250 #ifdef CONFIG_SND_DEBUG 251 { 252 unsigned int channel; 253 for (channel = 0; channel < plugin->src_format.channels; channel++) { 254 snd_assert(src_channels[channel].area.first % 8 == 0 && 255 src_channels[channel].area.step % 8 == 0, 256 return -ENXIO); 257 snd_assert(dst_channels[channel].area.first % 8 == 0 && 258 dst_channels[channel].area.step % 8 == 0, 259 return -ENXIO); 260 } 261 } 262 #endif 263 data = (struct mulaw_priv *)plugin->extra_data; 264 data->func(plugin, src_channels, dst_channels, frames); 265 return frames; 266 } 267 268 static int getput_index(int format) 269 { 270 int sign, width, endian; 271 sign = !snd_pcm_format_signed(format); 272 width = snd_pcm_format_width(format) / 8 - 1; 273 if (width < 0 || width > 3) { 274 snd_printk(KERN_ERR "snd-pcm-oss: invalid format %d\n", format); 275 width = 0; 276 } 277 #ifdef SNDRV_LITTLE_ENDIAN 278 endian = snd_pcm_format_big_endian(format); 279 #else 280 endian = snd_pcm_format_little_endian(format); 281 #endif 282 if (endian < 0) 283 endian = 0; 284 return width * 4 + endian * 2 + sign; 285 } 286 287 int snd_pcm_plugin_build_mulaw(struct snd_pcm_substream *plug, 288 struct snd_pcm_plugin_format *src_format, 289 struct snd_pcm_plugin_format *dst_format, 290 struct snd_pcm_plugin **r_plugin) 291 { 292 int err; 293 struct mulaw_priv *data; 294 struct snd_pcm_plugin *plugin; 295 struct snd_pcm_plugin_format *format; 296 mulaw_f func; 297 298 snd_assert(r_plugin != NULL, return -ENXIO); 299 *r_plugin = NULL; 300 301 snd_assert(src_format->rate == dst_format->rate, return -ENXIO); 302 snd_assert(src_format->channels == dst_format->channels, return -ENXIO); 303 304 if (dst_format->format == SNDRV_PCM_FORMAT_MU_LAW) { 305 format = src_format; 306 func = mulaw_encode; 307 } 308 else if (src_format->format == SNDRV_PCM_FORMAT_MU_LAW) { 309 format = dst_format; 310 func = mulaw_decode; 311 } 312 else { 313 snd_BUG(); 314 return -EINVAL; 315 } 316 snd_assert(snd_pcm_format_linear(format->format) != 0, return -ENXIO); 317 318 err = snd_pcm_plugin_build(plug, "Mu-Law<->linear conversion", 319 src_format, dst_format, 320 sizeof(struct mulaw_priv), &plugin); 321 if (err < 0) 322 return err; 323 data = (struct mulaw_priv *)plugin->extra_data; 324 data->func = func; 325 data->conv = getput_index(format->format); 326 snd_assert(data->conv >= 0 && data->conv < 4*2*2, return -EINVAL); 327 plugin->transfer = mulaw_transfer; 328 *r_plugin = plugin; 329 return 0; 330 } 331 332 #endif 333