xref: /linux/sound/core/oss/mulaw.c (revision 4b4193256c8d3bc3a5397b5cd9494c2ad386317d)
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 
val_seg(int val)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  */
linear2ulaw(int pcm_val)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  */
ulaw2linear(unsigned char u_val)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 
cvt_s16_to_native(struct mulaw_priv * data,unsigned char * dst,u16 sample)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 
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)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 
cvt_native_to_s16(struct mulaw_priv * data,unsigned char * src)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 
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)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 
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)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 
init_data(struct mulaw_priv * data,snd_pcm_format_t format)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 
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)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