core/oss/mulaw.c

0001 /*
0002  *  Mu-Law conversion Plug-In Interface
0003  *  Copyright (c) 1999 by Jaroslav Kysela <perex@perex.cz>
0004  *                        Uros Bizjak <uros@kss-loka.si>
0005  *
0006  *  Based on reference implementation by Sun Microsystems, Inc.
0007  *
0008  *   This library is free software; you can redistribute it and/or modify
0009  *   it under the terms of the GNU Library General Public License as
0010  *   published by the Free Software Foundation; either version 2 of
0011  *   the License, or (at your option) any later version.
0012  *
0013  *   This program is distributed in the hope that it will be useful,
0014  *   but WITHOUT ANY WARRANTY; without even the implied warranty of
0015  *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
0016  *   GNU Library General Public License for more details.
0017  *
0018  *   You should have received a copy of the GNU Library General Public
0019  *   License along with this library; if not, write to the Free Software
0020  *   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307 USA
0021  *
0022  */
0023
0024 #include <linux/time.h>
0025 #include <sound/core.h>
0026 #include <sound/pcm.h>
0027 #include "pcm_plugin.h"
0028
0029 #define SIGN_BIT    (0x80)      /* Sign bit for a u-law byte. */
0030 #define QUANT_MASK  (0xf)       /* Quantization field mask. */
0031 #define NSEGS       (8)     /* Number of u-law segments. */
0032 #define SEG_SHIFT   (4)     /* Left shift for segment number. */
0033 #define SEG_MASK    (0x70)      /* Segment field mask. */
0034
0035 static inline int val_seg(int val)
0036 {
0037     int r = 0;
0038     val >>= 7;
0039     if (val & 0xf0) {
0040         val >>= 4;
0041         r += 4;
0042     }
0043     if (val & 0x0c) {
0044         val >>= 2;
0045         r += 2;
0046     }
0047     if (val & 0x02)
0048         r += 1;
0049     return r;
0050 }
0051
0052 #define BIAS        (0x84)      /* Bias for linear code. */
0053
0054 /*
0055  * linear2ulaw() - Convert a linear PCM value to u-law
0056  *
0057  * In order to simplify the encoding process, the original linear magnitude
0058  * is biased by adding 33 which shifts the encoding range from (0 - 8158) to
0059  * (33 - 8191). The result can be seen in the following encoding table:
0060  *
0061  *  Biased Linear Input Code    Compressed Code
0062  *  ------------------------    ---------------
0063  *  00000001wxyza           000wxyz
0064  *  0000001wxyzab           001wxyz
0065  *  000001wxyzabc           010wxyz
0066  *  00001wxyzabcd           011wxyz
0067  *  0001wxyzabcde           100wxyz
0068  *  001wxyzabcdef           101wxyz
0069  *  01wxyzabcdefg           110wxyz
0070  *  1wxyzabcdefgh           111wxyz
0071  *
0072  * Each biased linear code has a leading 1 which identifies the segment
0073  * number. The value of the segment number is equal to 7 minus the number
0074  * of leading 0's. The quantization interval is directly available as the
0075  * four bits wxyz.  * The trailing bits (a - h) are ignored.
0076  *
0077  * Ordinarily the complement of the resulting code word is used for
0078  * transmission, and so the code word is complemented before it is returned.
0079  *
0080  * For further information see John C. Bellamy's Digital Telephony, 1982,
0081  * John Wiley & Sons, pps 98-111 and 472-476.
0082  */
0083 static unsigned char linear2ulaw(int pcm_val)   /* 2's complement (16-bit range) */
0084 {
0085     int mask;
0086     int seg;
0087     unsigned char uval;
0088
0089     /* Get the sign and the magnitude of the value. */
0090     if (pcm_val < 0) {
0091         pcm_val = BIAS - pcm_val;
0092         mask = 0x7F;
0093     } else {
0094         pcm_val += BIAS;
0095         mask = 0xFF;
0096     }
0097     if (pcm_val > 0x7FFF)
0098         pcm_val = 0x7FFF;
0099
0100     /* Convert the scaled magnitude to segment number. */
0101     seg = val_seg(pcm_val);
0102
0103     /*
0104      * Combine the sign, segment, quantization bits;
0105      * and complement the code word.
0106      */
0107     uval = (seg << 4) | ((pcm_val >> (seg + 3)) & 0xF);
0108     return uval ^ mask;
0109 }
0110
0111 /*
0112  * ulaw2linear() - Convert a u-law value to 16-bit linear PCM
0113  *
0114  * First, a biased linear code is derived from the code word. An unbiased
0115  * output can then be obtained by subtracting 33 from the biased code.
0116  *
0117  * Note that this function expects to be passed the complement of the
0118  * original code word. This is in keeping with ISDN conventions.
0119  */
0120 static int ulaw2linear(unsigned char u_val)
0121 {
0122     int t;
0123
0124     /* Complement to obtain normal u-law value. */
0125     u_val = ~u_val;
0126
0127     /*
0128      * Extract and bias the quantization bits. Then
0129      * shift up by the segment number and subtract out the bias.
0130      */
0131     t = ((u_val & QUANT_MASK) << 3) + BIAS;
0132     t <<= ((unsigned)u_val & SEG_MASK) >> SEG_SHIFT;
0133
0134     return ((u_val & SIGN_BIT) ? (BIAS - t) : (t - BIAS));
0135 }
0136
0137 /*
0138  *  Basic Mu-Law plugin
0139  */
0140
0141 typedef void (*mulaw_f)(struct snd_pcm_plugin *plugin,
0142             const struct snd_pcm_plugin_channel *src_channels,
0143             struct snd_pcm_plugin_channel *dst_channels,
0144             snd_pcm_uframes_t frames);
0145
0146 struct mulaw_priv {
0147     mulaw_f func;
0148     int cvt_endian;         /* need endian conversion? */
0149     unsigned int native_ofs;    /* byte offset in native format */
0150     unsigned int copy_ofs;      /* byte offset in s16 format */
0151     unsigned int native_bytes;  /* byte size of the native format */
0152     unsigned int copy_bytes;    /* bytes to copy per conversion */
0153     u16 flip; /* MSB flip for signedness, done after endian conversion */
0154 };
0155
0156 static inline void cvt_s16_to_native(struct mulaw_priv *data,
0157                      unsigned char *dst, u16 sample)
0158 {
0159     sample ^= data->flip;
0160     if (data->cvt_endian)
0161         sample = swab16(sample);
0162     if (data->native_bytes > data->copy_bytes)
0163         memset(dst, 0, data->native_bytes);
0164     memcpy(dst + data->native_ofs, (char *)&sample + data->copy_ofs,
0165            data->copy_bytes);
0166 }
0167
0168 static void mulaw_decode(struct snd_pcm_plugin *plugin,
0169             const struct snd_pcm_plugin_channel *src_channels,
0170             struct snd_pcm_plugin_channel *dst_channels,
0171             snd_pcm_uframes_t frames)
0172 {
0173     struct mulaw_priv *data = (struct mulaw_priv *)plugin->extra_data;
0174     int channel;
0175     int nchannels = plugin->src_format.channels;
0176     for (channel = 0; channel < nchannels; ++channel) {
0177         char *src;
0178         char *dst;
0179         int src_step, dst_step;
0180         snd_pcm_uframes_t frames1;
0181         if (!src_channels[channel].enabled) {
0182             if (dst_channels[channel].wanted)
0183                 snd_pcm_area_silence(&dst_channels[channel].area, 0, frames, plugin->dst_format.format);
0184             dst_channels[channel].enabled = 0;
0185             continue;
0186         }
0187         dst_channels[channel].enabled = 1;
0188         src = src_channels[channel].area.addr + src_channels[channel].area.first / 8;
0189         dst = dst_channels[channel].area.addr + dst_channels[channel].area.first / 8;
0190         src_step = src_channels[channel].area.step / 8;
0191         dst_step = dst_channels[channel].area.step / 8;
0192         frames1 = frames;
0193         while (frames1-- > 0) {
0194             signed short sample = ulaw2linear(*src);
0195             cvt_s16_to_native(data, dst, sample);
0196             src += src_step;
0197             dst += dst_step;
0198         }
0199     }
0200 }
0201
0202 static inline signed short cvt_native_to_s16(struct mulaw_priv *data,
0203                          unsigned char *src)
0204 {
0205     u16 sample = 0;
0206     memcpy((char *)&sample + data->copy_ofs, src + data->native_ofs,
0207            data->copy_bytes);
0208     if (data->cvt_endian)
0209         sample = swab16(sample);
0210     sample ^= data->flip;
0211     return (signed short)sample;
0212 }
0213
0214 static void mulaw_encode(struct snd_pcm_plugin *plugin,
0215             const struct snd_pcm_plugin_channel *src_channels,
0216             struct snd_pcm_plugin_channel *dst_channels,
0217             snd_pcm_uframes_t frames)
0218 {
0219     struct mulaw_priv *data = (struct mulaw_priv *)plugin->extra_data;
0220     int channel;
0221     int nchannels = plugin->src_format.channels;
0222     for (channel = 0; channel < nchannels; ++channel) {
0223         char *src;
0224         char *dst;
0225         int src_step, dst_step;
0226         snd_pcm_uframes_t frames1;
0227         if (!src_channels[channel].enabled) {
0228             if (dst_channels[channel].wanted)
0229                 snd_pcm_area_silence(&dst_channels[channel].area, 0, frames, plugin->dst_format.format);
0230             dst_channels[channel].enabled = 0;
0231             continue;
0232         }
0233         dst_channels[channel].enabled = 1;
0234         src = src_channels[channel].area.addr + src_channels[channel].area.first / 8;
0235         dst = dst_channels[channel].area.addr + dst_channels[channel].area.first / 8;
0236         src_step = src_channels[channel].area.step / 8;
0237         dst_step = dst_channels[channel].area.step / 8;
0238         frames1 = frames;
0239         while (frames1-- > 0) {
0240             signed short sample = cvt_native_to_s16(data, src);
0241             *dst = linear2ulaw(sample);
0242             src += src_step;
0243             dst += dst_step;
0244         }
0245     }
0246 }
0247
0248 static snd_pcm_sframes_t mulaw_transfer(struct snd_pcm_plugin *plugin,
0249                   const struct snd_pcm_plugin_channel *src_channels,
0250                   struct snd_pcm_plugin_channel *dst_channels,
0251                   snd_pcm_uframes_t frames)
0252 {
0253     struct mulaw_priv *data;
0254
0255     if (snd_BUG_ON(!plugin || !src_channels || !dst_channels))
0256         return -ENXIO;
0257     if (frames == 0)
0258         return 0;
0259 #ifdef CONFIG_SND_DEBUG
0260     {
0261         unsigned int channel;
0262         for (channel = 0; channel < plugin->src_format.channels; channel++) {
0263             if (snd_BUG_ON(src_channels[channel].area.first % 8 ||
0264                        src_channels[channel].area.step % 8))
0265                 return -ENXIO;
0266             if (snd_BUG_ON(dst_channels[channel].area.first % 8 ||
0267                        dst_channels[channel].area.step % 8))
0268                 return -ENXIO;
0269         }
0270     }
0271 #endif
0272     if (frames > dst_channels[0].frames)
0273         frames = dst_channels[0].frames;
0274     data = (struct mulaw_priv *)plugin->extra_data;
0275     data->func(plugin, src_channels, dst_channels, frames);
0276     return frames;
0277 }
0278
0279 static void init_data(struct mulaw_priv *data, snd_pcm_format_t format)
0280 {
0281 #ifdef SNDRV_LITTLE_ENDIAN
0282     data->cvt_endian = snd_pcm_format_big_endian(format) > 0;
0283 #else
0284     data->cvt_endian = snd_pcm_format_little_endian(format) > 0;
0285 #endif
0286     if (!snd_pcm_format_signed(format))
0287         data->flip = 0x8000;
0288     data->native_bytes = snd_pcm_format_physical_width(format) / 8;
0289     data->copy_bytes = data->native_bytes < 2 ? 1 : 2;
0290     if (snd_pcm_format_little_endian(format)) {
0291         data->native_ofs = data->native_bytes - data->copy_bytes;
0292         data->copy_ofs = 2 - data->copy_bytes;
0293     } else {
0294         /* S24 in 4bytes need an 1 byte offset */
0295         data->native_ofs = data->native_bytes -
0296             snd_pcm_format_width(format) / 8;
0297     }
0298 }
0299
0300 int snd_pcm_plugin_build_mulaw(struct snd_pcm_substream *plug,
0301                    struct snd_pcm_plugin_format *src_format,
0302                    struct snd_pcm_plugin_format *dst_format,
0303                    struct snd_pcm_plugin **r_plugin)
0304 {
0305     int err;
0306     struct mulaw_priv *data;
0307     struct snd_pcm_plugin *plugin;
0308     struct snd_pcm_plugin_format *format;
0309     mulaw_f func;
0310
0311     if (snd_BUG_ON(!r_plugin))
0312         return -ENXIO;
0313     *r_plugin = NULL;
0314
0315     if (snd_BUG_ON(src_format->rate != dst_format->rate))
0316         return -ENXIO;
0317     if (snd_BUG_ON(src_format->channels != dst_format->channels))
0318         return -ENXIO;
0319
0320     if (dst_format->format == SNDRV_PCM_FORMAT_MU_LAW) {
0321         format = src_format;
0322         func = mulaw_encode;
0323     }
0324     else if (src_format->format == SNDRV_PCM_FORMAT_MU_LAW) {
0325         format = dst_format;
0326         func = mulaw_decode;
0327     }
0328     else {
0329         snd_BUG();
0330         return -EINVAL;
0331     }
0332     if (!snd_pcm_format_linear(format->format))
0333         return -EINVAL;
0334
0335     err = snd_pcm_plugin_build(plug, "Mu-Law<->linear conversion",
0336                    src_format, dst_format,
0337                    sizeof(struct mulaw_priv), &plugin);
0338     if (err < 0)
0339         return err;
0340     data = (struct mulaw_priv *)plugin->extra_data;
0341     data->func = func;
0342     init_data(data, format->format);
0343     plugin->transfer = mulaw_transfer;
0344     *r_plugin = plugin;
0345     return 0;
0346 }