347 lines · c
1/*2 * Mu-Law conversion Plug-In Interface3 * 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 modify9 * it under the terms of the GNU Library General Public License as10 * published by the Free Software Foundation; either version 2 of11 * 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 of15 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the16 * GNU Library General Public License for more details.17 *18 * You should have received a copy of the GNU Library General Public19 * License along with this library; if not, write to the Free Software20 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA21 *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-law56 *57 * In order to simplify the encoding process, the original linear magnitude58 * is biased by adding 33 which shifts the encoding range from (0 - 8158) to59 * (33 - 8191). The result can be seen in the following encoding table:60 *61 * Biased Linear Input Code Compressed Code62 * ------------------------ ---------------63 * 00000001wxyza 000wxyz64 * 0000001wxyzab 001wxyz65 * 000001wxyzabc 010wxyz66 * 00001wxyzabcd 011wxyz67 * 0001wxyzabcde 100wxyz68 * 001wxyzabcdef 101wxyz69 * 01wxyzabcdefg 110wxyz70 * 1wxyzabcdefgh 111wxyz71 *72 * Each biased linear code has a leading 1 which identifies the segment73 * number. The value of the segment number is equal to 7 minus the number74 * of leading 0's. The quantization interval is directly available as the75 * four bits wxyz. * The trailing bits (a - h) are ignored.76 *77 * Ordinarily the complement of the resulting code word is used for78 * 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 PCM113 *114 * First, a biased linear code is derived from the code word. An unbiased115 * 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 the118 * 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. Then129 * 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 plugin139 */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_DEBUG260 {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#endif272 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 279static void init_data(struct mulaw_priv *data, snd_pcm_format_t format)280{281#ifdef SNDRV_LITTLE_ENDIAN282 data->cvt_endian = snd_pcm_format_big_endian(format) > 0;283#else284 data->cvt_endian = snd_pcm_format_little_endian(format) > 0;285#endif286 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 300int 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