sound/core/oss/mulaw.c

   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 <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)(struct snd_pcm_plugin *plugin,
 143                         const struct snd_pcm_plugin_channel *src_channels,
 144                         struct snd_pcm_plugin_channel *dst_channels,
 145                         snd_pcm_uframes_t frames);
 146
 147 struct mulaw_priv {
 148         mulaw_f func;
 149         int cvt_endian;                 /* need endian conversion? */
 150         unsigned int native_ofs;        /* byte offset in native format */
 151         unsigned int copy_ofs;          /* byte offset in s16 format */
 152         unsigned int native_bytes;      /* byte size of the native format */
 153         unsigned int copy_bytes;        /* bytes to copy per conversion */
 154         u16 flip; /* MSB flip for signedness, done after endian conversion */
 155 };
 156
 157 static inline void cvt_s16_to_native(struct mulaw_priv *data,
 158                                      unsigned char *dst, u16 sample)
 159 {
 160         sample ^= data->flip;
 161         if (data->cvt_endian)
 162                 sample = swab16(sample);
 163         if (data->native_bytes > data->copy_bytes)
 164                 memset(dst, 0, data->native_bytes);
 165         memcpy(dst + data->native_ofs, (char *)&sample + data->copy_ofs,
 166                data->copy_bytes);
 167 }
 168
 169 static void mulaw_decode(struct snd_pcm_plugin *plugin,
 170                         const struct snd_pcm_plugin_channel *src_channels,
 171                         struct snd_pcm_plugin_channel *dst_channels,
 172                         snd_pcm_uframes_t frames)
 173 {
 174         struct mulaw_priv *data = (struct mulaw_priv *)plugin->extra_data;
 175         int channel;
 176         int nchannels = plugin->src_format.channels;
 177         for (channel = 0; channel < nchannels; ++channel) {
 178                 char *src;
 179                 char *dst;
 180                 int src_step, dst_step;
 181                 snd_pcm_uframes_t frames1;
 182                 if (!src_channels[channel].enabled) {
 183                         if (dst_channels[channel].wanted)
 184                                 snd_pcm_area_silence(&dst_channels[channel].area, 0, frames, plugin->dst_format.format);
 185                         dst_channels[channel].enabled = 0;
 186                         continue;
 187                 }
 188                 dst_channels[channel].enabled = 1;
 189                 src = src_channels[channel].area.addr + src_channels[channel].area.first / 8;
 190                 dst = dst_channels[channel].area.addr + dst_channels[channel].area.first / 8;
 191                 src_step = src_channels[channel].area.step / 8;
 192                 dst_step = dst_channels[channel].area.step / 8;
 193                 frames1 = frames;
 194                 while (frames1-- > 0) {
 195                         signed short sample = ulaw2linear(*src);
 196                         cvt_s16_to_native(data, dst, sample);
 197                         src += src_step;
 198                         dst += dst_step;
 199                 }
 200         }
 201 }
 202
 203 static inline signed short cvt_native_to_s16(struct mulaw_priv *data,
 204                                              unsigned char *src)
 205 {
 206         u16 sample = 0;
 207         memcpy((char *)&sample + data->copy_ofs, src + data->native_ofs,
 208                data->copy_bytes);
 209         if (data->cvt_endian)
 210                 sample = swab16(sample);
 211         sample ^= data->flip;
 212         return (signed short)sample;
 213 }
 214
 215 static void mulaw_encode(struct snd_pcm_plugin *plugin,
 216                         const struct snd_pcm_plugin_channel *src_channels,
 217                         struct snd_pcm_plugin_channel *dst_channels,
 218                         snd_pcm_uframes_t frames)
 219 {
 220         struct mulaw_priv *data = (struct mulaw_priv *)plugin->extra_data;
 221         int channel;
 222         int nchannels = plugin->src_format.channels;
 223         for (channel = 0; channel < nchannels; ++channel) {
 224                 char *src;
 225                 char *dst;
 226                 int src_step, dst_step;
 227                 snd_pcm_uframes_t frames1;
 228                 if (!src_channels[channel].enabled) {
 229                         if (dst_channels[channel].wanted)
 230                                 snd_pcm_area_silence(&dst_channels[channel].area, 0, frames, plugin->dst_format.format);
 231                         dst_channels[channel].enabled = 0;
 232                         continue;
 233                 }
 234                 dst_channels[channel].enabled = 1;
 235                 src = src_channels[channel].area.addr + src_channels[channel].area.first / 8;
 236                 dst = dst_channels[channel].area.addr + dst_channels[channel].area.first / 8;
 237                 src_step = src_channels[channel].area.step / 8;
 238                 dst_step = dst_channels[channel].area.step / 8;
 239                 frames1 = frames;
 240                 while (frames1-- > 0) {
 241                         signed short sample = cvt_native_to_s16(data, src);
 242                         *dst = linear2ulaw(sample);
 243                         src += src_step;
 244                         dst += dst_step;
 245                 }
 246         }
 247 }
 248
 249 static snd_pcm_sframes_t mulaw_transfer(struct snd_pcm_plugin *plugin,
 250                               const struct snd_pcm_plugin_channel *src_channels,
 251                               struct snd_pcm_plugin_channel *dst_channels,
 252                               snd_pcm_uframes_t frames)
 253 {
 254         struct mulaw_priv *data;
 255
 256         snd_assert(plugin != NULL && src_channels != NULL && dst_channels != NULL, 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                         snd_assert(src_channels[channel].area.first % 8 == 0 &&
 264                                    src_channels[channel].area.step % 8 == 0,
 265                                    return -ENXIO);
 266                         snd_assert(dst_channels[channel].area.first % 8 == 0 &&
 267                                    dst_channels[channel].area.step % 8 == 0,
 268                                    return -ENXIO);
 269                 }
 270         }
 271 #endif
 272         data = (struct mulaw_priv *)plugin->extra_data;
 273         data->func(plugin, src_channels, dst_channels, frames);
 274         return frames;
 275 }
 276
 277 static void init_data(struct mulaw_priv *data, int format)
 278 {
 279 #ifdef SNDRV_LITTLE_ENDIAN
 280         data->cvt_endian = snd_pcm_format_big_endian(format) > 0;
 281 #else
 282         data->cvt_endian = snd_pcm_format_little_endian(format) > 0;
 283 #endif
 284         if (!snd_pcm_format_signed(format))
 285                 data->flip = 0x8000;
 286         data->native_bytes = snd_pcm_format_physical_width(format) / 8;
 287         data->copy_bytes = data->native_bytes < 2 ? 1 : 2;
 288         if (snd_pcm_format_little_endian(format)) {
 289                 data->native_ofs = data->native_bytes - data->copy_bytes;
 290                 data->copy_ofs = 2 - data->copy_bytes;
 291         } else {
 292                 /* S24 in 4bytes need an 1 byte offset */
 293                 data->native_ofs = data->native_bytes -
 294                         snd_pcm_format_width(format) / 8;
 295         }
 296 }
 297
 298 int snd_pcm_plugin_build_mulaw(struct snd_pcm_substream *plug,
 299                                struct snd_pcm_plugin_format *src_format,
 300                                struct snd_pcm_plugin_format *dst_format,
 301                                struct snd_pcm_plugin **r_plugin)
 302 {
 303         int err;
 304         struct mulaw_priv *data;
 305         struct snd_pcm_plugin *plugin;
 306         struct snd_pcm_plugin_format *format;
 307         mulaw_f func;
 308
 309         snd_assert(r_plugin != NULL, return -ENXIO);
 310         *r_plugin = NULL;
 311
 312         snd_assert(src_format->rate == dst_format->rate, return -ENXIO);
 313         snd_assert(src_format->channels == dst_format->channels, return -ENXIO);
 314
 315         if (dst_format->format == SNDRV_PCM_FORMAT_MU_LAW) {
 316                 format = src_format;
 317                 func = mulaw_encode;
 318         }
 319         else if (src_format->format == SNDRV_PCM_FORMAT_MU_LAW) {
 320                 format = dst_format;
 321                 func = mulaw_decode;
 322         }
 323         else {
 324                 snd_BUG();
 325                 return -EINVAL;
 326         }
 327         snd_assert(snd_pcm_format_linear(format->format) != 0, return -ENXIO);
 328
 329         err = snd_pcm_plugin_build(plug, "Mu-Law<->linear conversion",
 330                                    src_format, dst_format,
 331                                    sizeof(struct mulaw_priv), &plugin);
 332         if (err < 0)
 333                 return err;
 334         data = (struct mulaw_priv *)plugin->extra_data;
 335         data->func = func;
 336         init_data(data, format->format);
 337         plugin->transfer = mulaw_transfer;
 338         *r_plugin = plugin;
 339         return 0;
 340 }