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Linux/sound/core/oss/mulaw.c

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  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         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, snd_pcm_format_t 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         if (snd_BUG_ON(!r_plugin))
310                 return -ENXIO;
311         *r_plugin = NULL;
312 
313         if (snd_BUG_ON(src_format->rate != dst_format->rate))
314                 return -ENXIO;
315         if (snd_BUG_ON(src_format->channels != dst_format->channels))
316                 return -ENXIO;
317 
318         if (dst_format->format == SNDRV_PCM_FORMAT_MU_LAW) {
319                 format = src_format;
320                 func = mulaw_encode;
321         }
322         else if (src_format->format == SNDRV_PCM_FORMAT_MU_LAW) {
323                 format = dst_format;
324                 func = mulaw_decode;
325         }
326         else {
327                 snd_BUG();
328                 return -EINVAL;
329         }
330         if (snd_BUG_ON(!snd_pcm_format_linear(format->format)))
331                 return -ENXIO;
332 
333         err = snd_pcm_plugin_build(plug, "Mu-Law<->linear conversion",
334                                    src_format, dst_format,
335                                    sizeof(struct mulaw_priv), &plugin);
336         if (err < 0)
337                 return err;
338         data = (struct mulaw_priv *)plugin->extra_data;
339         data->func = func;
340         init_data(data, format->format);
341         plugin->transfer = mulaw_transfer;
342         *r_plugin = plugin;
343         return 0;
344 }
345 

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