root/sound/core/oss/mulaw.c

DEFINITIONS

1. val_seg
2. linear2ulaw
3. ulaw2linear
4. cvt_s16_to_native
5. mulaw_decode
6. cvt_native_to_s16
7. mulaw_encode
8. mulaw_transfer
9. init_data
10. snd_pcm_plugin_build_mulaw

   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_BUG_ON(!snd_pcm_format_linear(format->format)))
 333                 return -ENXIO;
 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 }