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_pcm_format_linear(format->format))
333 return -EINVAL;
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 }
347
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