summaryrefslogtreecommitdiff
path: root/sound/core/oss/mulaw.c
blob: 3da3b81626d311fd7a5c8fa3c7386fb31d8791ca (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
/*
 *  Mu-Law conversion Plug-In Interface
 *  Copyright (c) 1999 by Jaroslav Kysela <perex@suse.cz>
 *                        Uros Bizjak <uros@kss-loka.si>
 *
 *  Based on reference implementation by Sun Microsystems, Inc.
 *
 *   This library is free software; you can redistribute it and/or modify
 *   it under the terms of the GNU Library General Public License as
 *   published by the Free Software Foundation; either version 2 of
 *   the License, or (at your option) any later version.
 *
 *   This program is distributed in the hope that it will be useful,
 *   but WITHOUT ANY WARRANTY; without even the implied warranty of
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *   GNU Library General Public License for more details.
 *
 *   You should have received a copy of the GNU Library General Public
 *   License along with this library; if not, write to the Free Software
 *   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307 USA
 *
 */
  
#include <sound/driver.h>
#include <linux/time.h>
#include <sound/core.h>
#include <sound/pcm.h>
#include "pcm_plugin.h"

#define	SIGN_BIT	(0x80)		/* Sign bit for a u-law byte. */
#define	QUANT_MASK	(0xf)		/* Quantization field mask. */
#define	NSEGS		(8)		/* Number of u-law segments. */
#define	SEG_SHIFT	(4)		/* Left shift for segment number. */
#define	SEG_MASK	(0x70)		/* Segment field mask. */

static inline int val_seg(int val)
{
	int r = 0;
	val >>= 7;
	if (val & 0xf0) {
		val >>= 4;
		r += 4;
	}
	if (val & 0x0c) {
		val >>= 2;
		r += 2;
	}
	if (val & 0x02)
		r += 1;
	return r;
}

#define	BIAS		(0x84)		/* Bias for linear code. */

/*
 * linear2ulaw() - Convert a linear PCM value to u-law
 *
 * In order to simplify the encoding process, the original linear magnitude
 * is biased by adding 33 which shifts the encoding range from (0 - 8158) to
 * (33 - 8191). The result can be seen in the following encoding table:
 *
 *	Biased Linear Input Code	Compressed Code
 *	------------------------	---------------
 *	00000001wxyza			000wxyz
 *	0000001wxyzab			001wxyz
 *	000001wxyzabc			010wxyz
 *	00001wxyzabcd			011wxyz
 *	0001wxyzabcde			100wxyz
 *	001wxyzabcdef			101wxyz
 *	01wxyzabcdefg			110wxyz
 *	1wxyzabcdefgh			111wxyz
 *
 * Each biased linear code has a leading 1 which identifies the segment
 * number. The value of the segment number is equal to 7 minus the number
 * of leading 0's. The quantization interval is directly available as the
 * four bits wxyz.  * The trailing bits (a - h) are ignored.
 *
 * Ordinarily the complement of the resulting code word is used for
 * transmission, and so the code word is complemented before it is returned.
 *
 * For further information see John C. Bellamy's Digital Telephony, 1982,
 * John Wiley & Sons, pps 98-111 and 472-476.
 */
static unsigned char linear2ulaw(int pcm_val)	/* 2's complement (16-bit range) */
{
	int mask;
	int seg;
	unsigned char uval;

	/* Get the sign and the magnitude of the value. */
	if (pcm_val < 0) {
		pcm_val = BIAS - pcm_val;
		mask = 0x7F;
	} else {
		pcm_val += BIAS;
		mask = 0xFF;
	}
	if (pcm_val > 0x7FFF)
		pcm_val = 0x7FFF;

	/* Convert the scaled magnitude to segment number. */
	seg = val_seg(pcm_val);

	/*
	 * Combine the sign, segment, quantization bits;
	 * and complement the code word.
	 */
	uval = (seg << 4) | ((pcm_val >> (seg + 3)) & 0xF);
	return uval ^ mask;
}

/*
 * ulaw2linear() - Convert a u-law value to 16-bit linear PCM
 *
 * First, a biased linear code is derived from the code word. An unbiased
 * output can then be obtained by subtracting 33 from the biased code.
 *
 * Note that this function expects to be passed the complement of the
 * original code word. This is in keeping with ISDN conventions.
 */
static int ulaw2linear(unsigned char u_val)
{
	int t;

	/* Complement to obtain normal u-law value. */
	u_val = ~u_val;

	/*
	 * Extract and bias the quantization bits. Then
	 * shift up by the segment number and subtract out the bias.
	 */
	t = ((u_val & QUANT_MASK) << 3) + BIAS;
	t <<= ((unsigned)u_val & SEG_MASK) >> SEG_SHIFT;

	return ((u_val & SIGN_BIT) ? (BIAS - t) : (t - BIAS));
}

/*
 *  Basic Mu-Law plugin
 */

typedef void (*mulaw_f)(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);

struct mulaw_priv {
	mulaw_f func;
	int cvt_endian;			/* need endian conversion? */
	unsigned int native_ofs;	/* byte offset in native format */
	unsigned int copy_ofs;		/* byte offset in s16 format */
	unsigned int native_bytes;	/* byte size of the native format */
	unsigned int copy_bytes;	/* bytes to copy per conversion */
	u16 flip; /* MSB flip for signedness, done after endian conversion */
};

static inline void cvt_s16_to_native(struct mulaw_priv *data,
				     unsigned char *dst, u16 sample)
{
	sample ^= data->flip;
	if (data->cvt_endian)
		sample = swab16(sample);
	if (data->native_bytes > data->copy_bytes)
		memset(dst, 0, data->native_bytes);
	memcpy(dst + data->native_ofs, (char *)&sample + data->copy_ofs,
	       data->copy_bytes);
}

static void 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)
{
	struct mulaw_priv *data = (struct mulaw_priv *)plugin->extra_data;
	int channel;
	int nchannels = plugin->src_format.channels;
	for (channel = 0; channel < nchannels; ++channel) {
		char *src;
		char *dst;
		int src_step, dst_step;
		snd_pcm_uframes_t frames1;
		if (!src_channels[channel].enabled) {
			if (dst_channels[channel].wanted)
				snd_pcm_area_silence(&dst_channels[channel].area, 0, frames, plugin->dst_format.format);
			dst_channels[channel].enabled = 0;
			continue;
		}
		dst_channels[channel].enabled = 1;
		src = src_channels[channel].area.addr + src_channels[channel].area.first / 8;
		dst = dst_channels[channel].area.addr + dst_channels[channel].area.first / 8;
		src_step = src_channels[channel].area.step / 8;
		dst_step = dst_channels[channel].area.step / 8;
		frames1 = frames;
		while (frames1-- > 0) {
			signed short sample = ulaw2linear(*src);
			cvt_s16_to_native(data, dst, sample);
			src += src_step;
			dst += dst_step;
		}
	}
}

static inline signed short cvt_native_to_s16(struct mulaw_priv *data,
					     unsigned char *src)
{
	u16 sample = 0;
	memcpy((char *)&sample + data->copy_ofs, src + data->native_ofs,
	       data->copy_bytes);
	if (data->cvt_endian)
		sample = swab16(sample);
	sample ^= data->flip;
	return (signed short)sample;
}

static void 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)
{
	struct mulaw_priv *data = (struct mulaw_priv *)plugin->extra_data;
	int channel;
	int nchannels = plugin->src_format.channels;
	for (channel = 0; channel < nchannels; ++channel) {
		char *src;
		char *dst;
		int src_step, dst_step;
		snd_pcm_uframes_t frames1;
		if (!src_channels[channel].enabled) {
			if (dst_channels[channel].wanted)
				snd_pcm_area_silence(&dst_channels[channel].area, 0, frames, plugin->dst_format.format);
			dst_channels[channel].enabled = 0;
			continue;
		}
		dst_channels[channel].enabled = 1;
		src = src_channels[channel].area.addr + src_channels[channel].area.first / 8;
		dst = dst_channels[channel].area.addr + dst_channels[channel].area.first / 8;
		src_step = src_channels[channel].area.step / 8;
		dst_step = dst_channels[channel].area.step / 8;
		frames1 = frames;
		while (frames1-- > 0) {
			signed short sample = cvt_native_to_s16(data, src);
			*dst = linear2ulaw(sample);
			src += src_step;
			dst += dst_step;
		}
	}
}

static snd_pcm_sframes_t 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)
{
	struct mulaw_priv *data;

	snd_assert(plugin != NULL && src_channels != NULL && dst_channels != NULL, return -ENXIO);
	if (frames == 0)
		return 0;
#ifdef CONFIG_SND_DEBUG
	{
		unsigned int channel;
		for (channel = 0; channel < plugin->src_format.channels; channel++) {
			snd_assert(src_channels[channel].area.first % 8 == 0 &&
				   src_channels[channel].area.step % 8 == 0,
				   return -ENXIO);
			snd_assert(dst_channels[channel].area.first % 8 == 0 &&
				   dst_channels[channel].area.step % 8 == 0,
				   return -ENXIO);
		}
	}
#endif
	data = (struct mulaw_priv *)plugin->extra_data;
	data->func(plugin, src_channels, dst_channels, frames);
	return frames;
}

static void init_data(struct mulaw_priv *data, int format)
{
#ifdef SNDRV_LITTLE_ENDIAN
	data->cvt_endian = snd_pcm_format_big_endian(format) > 0;
#else
	data->cvt_endian = snd_pcm_format_little_endian(format) > 0;
#endif
	if (!snd_pcm_format_signed(format))
		data->flip = 0x8000;
	data->native_bytes = snd_pcm_format_physical_width(format) / 8;
	data->copy_bytes = data->native_bytes < 2 ? 1 : 2;
	if (snd_pcm_format_little_endian(format)) {
		data->native_ofs = data->native_bytes - data->copy_bytes;
		data->copy_ofs = 2 - data->copy_bytes;
	} else {
		/* S24 in 4bytes need an 1 byte offset */
		data->native_ofs = data->native_bytes -
			snd_pcm_format_width(format) / 8;
	}
}

int 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)
{
	int err;
	struct mulaw_priv *data;
	struct snd_pcm_plugin *plugin;
	struct snd_pcm_plugin_format *format;
	mulaw_f func;

	snd_assert(r_plugin != NULL, return -ENXIO);
	*r_plugin = NULL;

	snd_assert(src_format->rate == dst_format->rate, return -ENXIO);
	snd_assert(src_format->channels == dst_format->channels, return -ENXIO);

	if (dst_format->format == SNDRV_PCM_FORMAT_MU_LAW) {
		format = src_format;
		func = mulaw_encode;
	}
	else if (src_format->format == SNDRV_PCM_FORMAT_MU_LAW) {
		format = dst_format;
		func = mulaw_decode;
	}
	else {
		snd_BUG();
		return -EINVAL;
	}
	snd_assert(snd_pcm_format_linear(format->format) != 0, return -ENXIO);

	err = snd_pcm_plugin_build(plug, "Mu-Law<->linear conversion",
				   src_format, dst_format,
				   sizeof(struct mulaw_priv), &plugin);
	if (err < 0)
		return err;
	data = (struct mulaw_priv *)plugin->extra_data;
	data->func = func;
	init_data(data, format->format);
	plugin->transfer = mulaw_transfer;
	*r_plugin = plugin;
	return 0;
}