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mulaw.c

/*
 *  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)(snd_pcm_plugin_t *plugin,
                  const snd_pcm_plugin_channel_t *src_channels,
                  snd_pcm_plugin_channel_t *dst_channels,
                  snd_pcm_uframes_t frames);

typedef struct mulaw_private_data {
      mulaw_f func;
      int conv;
} mulaw_t;

static void mulaw_decode(snd_pcm_plugin_t *plugin,
                  const snd_pcm_plugin_channel_t *src_channels,
                  snd_pcm_plugin_channel_t *dst_channels,
                  snd_pcm_uframes_t frames)
{
#define PUT_S16_LABELS
#include "plugin_ops.h"
#undef PUT_S16_LABELS
      mulaw_t *data = (mulaw_t *)plugin->extra_data;
      void *put = put_s16_labels[data->conv];
      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);
                  goto *put;
#define PUT_S16_END after
#include "plugin_ops.h"
#undef PUT_S16_END
            after:
                  src += src_step;
                  dst += dst_step;
            }
      }
}

static void mulaw_encode(snd_pcm_plugin_t *plugin,
                  const snd_pcm_plugin_channel_t *src_channels,
                  snd_pcm_plugin_channel_t *dst_channels,
                  snd_pcm_uframes_t frames)
{
#define GET_S16_LABELS
#include "plugin_ops.h"
#undef GET_S16_LABELS
      mulaw_t *data = (mulaw_t *)plugin->extra_data;
      void *get = get_s16_labels[data->conv];
      int channel;
      int nchannels = plugin->src_format.channels;
      signed short sample = 0;
      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) {
                  goto *get;
#define GET_S16_END after
#include "plugin_ops.h"
#undef GET_S16_END
            after:
                  *dst = linear2ulaw(sample);
                  src += src_step;
                  dst += dst_step;
            }
      }
}

static snd_pcm_sframes_t mulaw_transfer(snd_pcm_plugin_t *plugin,
                        const snd_pcm_plugin_channel_t *src_channels,
                        snd_pcm_plugin_channel_t *dst_channels,
                        snd_pcm_uframes_t frames)
{
      mulaw_t *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 = (mulaw_t *)plugin->extra_data;
      data->func(plugin, src_channels, dst_channels, frames);
      return frames;
}

int snd_pcm_plugin_build_mulaw(snd_pcm_plug_t *plug,
                         snd_pcm_plugin_format_t *src_format,
                         snd_pcm_plugin_format_t *dst_format,
                         snd_pcm_plugin_t **r_plugin)
{
      int err;
      mulaw_t *data;
      snd_pcm_plugin_t *plugin;
      snd_pcm_plugin_format_t *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(mulaw_t), &plugin);
      if (err < 0)
            return err;
      data = (mulaw_t*)plugin->extra_data;
      data->func = func;
      data->conv = getput_index(format->format);
      snd_assert(data->conv >= 0 && data->conv < 4*2*2, return -EINVAL);
      plugin->transfer = mulaw_transfer;
      *r_plugin = plugin;
      return 0;
}

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