sound/core/oss/mulaw.c

   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 }