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