1 // SPDX-License-Identifier: LGPL-2.0+
2 /*
3 * Mu-Law conversion Plug-In Interface
4 * Copyright (c) 1999 by Jaroslav Kysela <perex@perex.cz>
5 * Uros Bizjak <uros@kss-loka.si>
6 *
7 * Based on reference implementation by Sun Microsystems, Inc.
8 */
9
10 #include <linux/time.h>
11 #include <sound/core.h>
12 #include <sound/pcm.h>
13 #include "pcm_plugin.h"
14
15 #define SIGN_BIT (0x80) /* Sign bit for a u-law byte. */
16 #define QUANT_MASK (0xf) /* Quantization field mask. */
17 #define NSEGS (8) /* Number of u-law segments. */
18 #define SEG_SHIFT (4) /* Left shift for segment number. */
19 #define SEG_MASK (0x70) /* Segment field mask. */
20
val_seg(int val)21 static inline int val_seg(int val)
22 {
23 int r = 0;
24 val >>= 7;
25 if (val & 0xf0) {
26 val >>= 4;
27 r += 4;
28 }
29 if (val & 0x0c) {
30 val >>= 2;
31 r += 2;
32 }
33 if (val & 0x02)
34 r += 1;
35 return r;
36 }
37
38 #define BIAS (0x84) /* Bias for linear code. */
39
40 /*
41 * linear2ulaw() - Convert a linear PCM value to u-law
42 *
43 * In order to simplify the encoding process, the original linear magnitude
44 * is biased by adding 33 which shifts the encoding range from (0 - 8158) to
45 * (33 - 8191). The result can be seen in the following encoding table:
46 *
47 * Biased Linear Input Code Compressed Code
48 * ------------------------ ---------------
49 * 00000001wxyza 000wxyz
50 * 0000001wxyzab 001wxyz
51 * 000001wxyzabc 010wxyz
52 * 00001wxyzabcd 011wxyz
53 * 0001wxyzabcde 100wxyz
54 * 001wxyzabcdef 101wxyz
55 * 01wxyzabcdefg 110wxyz
56 * 1wxyzabcdefgh 111wxyz
57 *
58 * Each biased linear code has a leading 1 which identifies the segment
59 * number. The value of the segment number is equal to 7 minus the number
60 * of leading 0's. The quantization interval is directly available as the
61 * four bits wxyz. * The trailing bits (a - h) are ignored.
62 *
63 * Ordinarily the complement of the resulting code word is used for
64 * transmission, and so the code word is complemented before it is returned.
65 *
66 * For further information see John C. Bellamy's Digital Telephony, 1982,
67 * John Wiley & Sons, pps 98-111 and 472-476.
68 */
linear2ulaw(int pcm_val)69 static unsigned char linear2ulaw(int pcm_val) /* 2's complement (16-bit range) */
70 {
71 int mask;
72 int seg;
73 unsigned char uval;
74
75 /* Get the sign and the magnitude of the value. */
76 if (pcm_val < 0) {
77 pcm_val = BIAS - pcm_val;
78 mask = 0x7F;
79 } else {
80 pcm_val += BIAS;
81 mask = 0xFF;
82 }
83 if (pcm_val > 0x7FFF)
84 pcm_val = 0x7FFF;
85
86 /* Convert the scaled magnitude to segment number. */
87 seg = val_seg(pcm_val);
88
89 /*
90 * Combine the sign, segment, quantization bits;
91 * and complement the code word.
92 */
93 uval = (seg << 4) | ((pcm_val >> (seg + 3)) & 0xF);
94 return uval ^ mask;
95 }
96
97 /*
98 * ulaw2linear() - Convert a u-law value to 16-bit linear PCM
99 *
100 * First, a biased linear code is derived from the code word. An unbiased
101 * output can then be obtained by subtracting 33 from the biased code.
102 *
103 * Note that this function expects to be passed the complement of the
104 * original code word. This is in keeping with ISDN conventions.
105 */
ulaw2linear(unsigned char u_val)106 static int ulaw2linear(unsigned char u_val)
107 {
108 int t;
109
110 /* Complement to obtain normal u-law value. */
111 u_val = ~u_val;
112
113 /*
114 * Extract and bias the quantization bits. Then
115 * shift up by the segment number and subtract out the bias.
116 */
117 t = ((u_val & QUANT_MASK) << 3) + BIAS;
118 t <<= ((unsigned)u_val & SEG_MASK) >> SEG_SHIFT;
119
120 return ((u_val & SIGN_BIT) ? (BIAS - t) : (t - BIAS));
121 }
122
123 /*
124 * Basic Mu-Law plugin
125 */
126
127 typedef void (*mulaw_f)(struct snd_pcm_plugin *plugin,
128 const struct snd_pcm_plugin_channel *src_channels,
129 struct snd_pcm_plugin_channel *dst_channels,
130 snd_pcm_uframes_t frames);
131
132 struct mulaw_priv {
133 mulaw_f func;
134 int cvt_endian; /* need endian conversion? */
135 unsigned int native_ofs; /* byte offset in native format */
136 unsigned int copy_ofs; /* byte offset in s16 format */
137 unsigned int native_bytes; /* byte size of the native format */
138 unsigned int copy_bytes; /* bytes to copy per conversion */
139 u16 flip; /* MSB flip for signedness, done after endian conversion */
140 };
141
cvt_s16_to_native(struct mulaw_priv * data,unsigned char * dst,u16 sample)142 static inline void cvt_s16_to_native(struct mulaw_priv *data,
143 unsigned char *dst, u16 sample)
144 {
145 sample ^= data->flip;
146 if (data->cvt_endian)
147 sample = swab16(sample);
148 if (data->native_bytes > data->copy_bytes)
149 memset(dst, 0, data->native_bytes);
150 memcpy(dst + data->native_ofs, (char *)&sample + data->copy_ofs,
151 data->copy_bytes);
152 }
153
mulaw_decode(struct snd_pcm_plugin * plugin,const struct snd_pcm_plugin_channel * src_channels,struct snd_pcm_plugin_channel * dst_channels,snd_pcm_uframes_t frames)154 static void mulaw_decode(struct snd_pcm_plugin *plugin,
155 const struct snd_pcm_plugin_channel *src_channels,
156 struct snd_pcm_plugin_channel *dst_channels,
157 snd_pcm_uframes_t frames)
158 {
159 struct mulaw_priv *data = (struct mulaw_priv *)plugin->extra_data;
160 int channel;
161 int nchannels = plugin->src_format.channels;
162 for (channel = 0; channel < nchannels; ++channel) {
163 char *src;
164 char *dst;
165 int src_step, dst_step;
166 snd_pcm_uframes_t frames1;
167 if (!src_channels[channel].enabled) {
168 if (dst_channels[channel].wanted)
169 snd_pcm_area_silence(&dst_channels[channel].area, 0, frames, plugin->dst_format.format);
170 dst_channels[channel].enabled = 0;
171 continue;
172 }
173 dst_channels[channel].enabled = 1;
174 src = src_channels[channel].area.addr + src_channels[channel].area.first / 8;
175 dst = dst_channels[channel].area.addr + dst_channels[channel].area.first / 8;
176 src_step = src_channels[channel].area.step / 8;
177 dst_step = dst_channels[channel].area.step / 8;
178 frames1 = frames;
179 while (frames1-- > 0) {
180 signed short sample = ulaw2linear(*src);
181 cvt_s16_to_native(data, dst, sample);
182 src += src_step;
183 dst += dst_step;
184 }
185 }
186 }
187
cvt_native_to_s16(struct mulaw_priv * data,unsigned char * src)188 static inline signed short cvt_native_to_s16(struct mulaw_priv *data,
189 unsigned char *src)
190 {
191 u16 sample = 0;
192 memcpy((char *)&sample + data->copy_ofs, src + data->native_ofs,
193 data->copy_bytes);
194 if (data->cvt_endian)
195 sample = swab16(sample);
196 sample ^= data->flip;
197 return (signed short)sample;
198 }
199
mulaw_encode(struct snd_pcm_plugin * plugin,const struct snd_pcm_plugin_channel * src_channels,struct snd_pcm_plugin_channel * dst_channels,snd_pcm_uframes_t frames)200 static void mulaw_encode(struct snd_pcm_plugin *plugin,
201 const struct snd_pcm_plugin_channel *src_channels,
202 struct snd_pcm_plugin_channel *dst_channels,
203 snd_pcm_uframes_t frames)
204 {
205 struct mulaw_priv *data = (struct mulaw_priv *)plugin->extra_data;
206 int channel;
207 int nchannels = plugin->src_format.channels;
208 for (channel = 0; channel < nchannels; ++channel) {
209 char *src;
210 char *dst;
211 int src_step, dst_step;
212 snd_pcm_uframes_t frames1;
213 if (!src_channels[channel].enabled) {
214 if (dst_channels[channel].wanted)
215 snd_pcm_area_silence(&dst_channels[channel].area, 0, frames, plugin->dst_format.format);
216 dst_channels[channel].enabled = 0;
217 continue;
218 }
219 dst_channels[channel].enabled = 1;
220 src = src_channels[channel].area.addr + src_channels[channel].area.first / 8;
221 dst = dst_channels[channel].area.addr + dst_channels[channel].area.first / 8;
222 src_step = src_channels[channel].area.step / 8;
223 dst_step = dst_channels[channel].area.step / 8;
224 frames1 = frames;
225 while (frames1-- > 0) {
226 signed short sample = cvt_native_to_s16(data, src);
227 *dst = linear2ulaw(sample);
228 src += src_step;
229 dst += dst_step;
230 }
231 }
232 }
233
mulaw_transfer(struct snd_pcm_plugin * plugin,const struct snd_pcm_plugin_channel * src_channels,struct snd_pcm_plugin_channel * dst_channels,snd_pcm_uframes_t frames)234 static snd_pcm_sframes_t mulaw_transfer(struct snd_pcm_plugin *plugin,
235 const struct snd_pcm_plugin_channel *src_channels,
236 struct snd_pcm_plugin_channel *dst_channels,
237 snd_pcm_uframes_t frames)
238 {
239 struct mulaw_priv *data;
240
241 if (snd_BUG_ON(!plugin || !src_channels || !dst_channels))
242 return -ENXIO;
243 if (frames == 0)
244 return 0;
245 #ifdef CONFIG_SND_DEBUG
246 {
247 unsigned int channel;
248 for (channel = 0; channel < plugin->src_format.channels; channel++) {
249 if (snd_BUG_ON(src_channels[channel].area.first % 8 ||
250 src_channels[channel].area.step % 8))
251 return -ENXIO;
252 if (snd_BUG_ON(dst_channels[channel].area.first % 8 ||
253 dst_channels[channel].area.step % 8))
254 return -ENXIO;
255 }
256 }
257 #endif
258 if (frames > dst_channels[0].frames)
259 frames = dst_channels[0].frames;
260 data = (struct mulaw_priv *)plugin->extra_data;
261 data->func(plugin, src_channels, dst_channels, frames);
262 return frames;
263 }
264
init_data(struct mulaw_priv * data,snd_pcm_format_t format)265 static void init_data(struct mulaw_priv *data, snd_pcm_format_t format)
266 {
267 #ifdef SNDRV_LITTLE_ENDIAN
268 data->cvt_endian = snd_pcm_format_big_endian(format) > 0;
269 #else
270 data->cvt_endian = snd_pcm_format_little_endian(format) > 0;
271 #endif
272 if (!snd_pcm_format_signed(format))
273 data->flip = 0x8000;
274 data->native_bytes = snd_pcm_format_physical_width(format) / 8;
275 data->copy_bytes = data->native_bytes < 2 ? 1 : 2;
276 if (snd_pcm_format_little_endian(format)) {
277 data->native_ofs = data->native_bytes - data->copy_bytes;
278 data->copy_ofs = 2 - data->copy_bytes;
279 } else {
280 /* S24 in 4bytes need an 1 byte offset */
281 data->native_ofs = data->native_bytes -
282 snd_pcm_format_width(format) / 8;
283 }
284 }
285
snd_pcm_plugin_build_mulaw(struct snd_pcm_substream * plug,struct snd_pcm_plugin_format * src_format,struct snd_pcm_plugin_format * dst_format,struct snd_pcm_plugin ** r_plugin)286 int snd_pcm_plugin_build_mulaw(struct snd_pcm_substream *plug,
287 struct snd_pcm_plugin_format *src_format,
288 struct snd_pcm_plugin_format *dst_format,
289 struct snd_pcm_plugin **r_plugin)
290 {
291 int err;
292 struct mulaw_priv *data;
293 struct snd_pcm_plugin *plugin;
294 struct snd_pcm_plugin_format *format;
295 mulaw_f func;
296
297 if (snd_BUG_ON(!r_plugin))
298 return -ENXIO;
299 *r_plugin = NULL;
300
301 if (snd_BUG_ON(src_format->rate != dst_format->rate))
302 return -ENXIO;
303 if (snd_BUG_ON(src_format->channels != dst_format->channels))
304 return -ENXIO;
305
306 if (dst_format->format == SNDRV_PCM_FORMAT_MU_LAW) {
307 format = src_format;
308 func = mulaw_encode;
309 }
310 else if (src_format->format == SNDRV_PCM_FORMAT_MU_LAW) {
311 format = dst_format;
312 func = mulaw_decode;
313 }
314 else {
315 snd_BUG();
316 return -EINVAL;
317 }
318 if (!snd_pcm_format_linear(format->format))
319 return -EINVAL;
320
321 err = snd_pcm_plugin_build(plug, "Mu-Law<->linear conversion",
322 src_format, dst_format,
323 sizeof(struct mulaw_priv), &plugin);
324 if (err < 0)
325 return err;
326 data = (struct mulaw_priv *)plugin->extra_data;
327 data->func = func;
328 init_data(data, format->format);
329 plugin->transfer = mulaw_transfer;
330 *r_plugin = plugin;
331 return 0;
332 }
333