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mulaw.c
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1 /*
2  * Mu-Law conversion Plug-In Interface
3  * Copyright (c) 1999 by Jaroslav Kysela <[email protected]>
4  * Uros Bizjak <[email protected]>
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 }
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