Root/sound/core/oss/mulaw.c

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
35static 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 */
83static 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 */
120static 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
141typedef 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
146struct 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
156static 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
168static 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
202static 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
214static 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
248static 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
277static 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
298int 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}
345

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