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pcm_plugin.c

/*
 *  PCM Plug-In shared (kernel/library) code
 *  Copyright (c) 1999 by Jaroslav Kysela <perex@perex.cz>
 *  Copyright (c) 2000 by Abramo Bagnara <abramo@alsa-project.org>
 *
 *
 *   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
 *
 */
  
#if 0
#define PLUGIN_DEBUG
#endif

#include <linux/slab.h>
#include <linux/time.h>
#include <linux/vmalloc.h>
#include <sound/core.h>
#include <sound/pcm.h>
#include <sound/pcm_params.h>
#include "pcm_plugin.h"

#define snd_pcm_plug_first(plug) ((plug)->runtime->oss.plugin_first)
#define snd_pcm_plug_last(plug) ((plug)->runtime->oss.plugin_last)

/*
 *  because some cards might have rates "very close", we ignore
 *  all "resampling" requests within +-5%
 */
static int rate_match(unsigned int src_rate, unsigned int dst_rate)
{
      unsigned int low = (src_rate * 95) / 100;
      unsigned int high = (src_rate * 105) / 100;
      return dst_rate >= low && dst_rate <= high;
}

static int snd_pcm_plugin_alloc(struct snd_pcm_plugin *plugin, snd_pcm_uframes_t frames)
{
      struct snd_pcm_plugin_format *format;
      ssize_t width;
      size_t size;
      unsigned int channel;
      struct snd_pcm_plugin_channel *c;

      if (plugin->stream == SNDRV_PCM_STREAM_PLAYBACK) {
            format = &plugin->src_format;
      } else {
            format = &plugin->dst_format;
      }
      if ((width = snd_pcm_format_physical_width(format->format)) < 0)
            return width;
      size = frames * format->channels * width;
      snd_assert((size % 8) == 0, return -ENXIO);
      size /= 8;
      if (plugin->buf_frames < frames) {
            vfree(plugin->buf);
            plugin->buf = vmalloc(size);
            plugin->buf_frames = frames;
      }
      if (!plugin->buf) {
            plugin->buf_frames = 0;
            return -ENOMEM;
      }
      c = plugin->buf_channels;
      if (plugin->access == SNDRV_PCM_ACCESS_RW_INTERLEAVED) {
            for (channel = 0; channel < format->channels; channel++, c++) {
                  c->frames = frames;
                  c->enabled = 1;
                  c->wanted = 0;
                  c->area.addr = plugin->buf;
                  c->area.first = channel * width;
                  c->area.step = format->channels * width;
            }
      } else if (plugin->access == SNDRV_PCM_ACCESS_RW_NONINTERLEAVED) {
            snd_assert((size % format->channels) == 0,);
            size /= format->channels;
            for (channel = 0; channel < format->channels; channel++, c++) {
                  c->frames = frames;
                  c->enabled = 1;
                  c->wanted = 0;
                  c->area.addr = plugin->buf + (channel * size);
                  c->area.first = 0;
                  c->area.step = width;
            }
      } else
            return -EINVAL;
      return 0;
}

int snd_pcm_plug_alloc(struct snd_pcm_substream *plug, snd_pcm_uframes_t frames)
{
      int err;
      snd_assert(snd_pcm_plug_first(plug) != NULL, return -ENXIO);
      if (snd_pcm_plug_stream(plug) == SNDRV_PCM_STREAM_PLAYBACK) {
            struct snd_pcm_plugin *plugin = snd_pcm_plug_first(plug);
            while (plugin->next) {
                  if (plugin->dst_frames)
                        frames = plugin->dst_frames(plugin, frames);
                  snd_assert(frames > 0, return -ENXIO);
                  plugin = plugin->next;
                  err = snd_pcm_plugin_alloc(plugin, frames);
                  if (err < 0)
                        return err;
            }
      } else {
            struct snd_pcm_plugin *plugin = snd_pcm_plug_last(plug);
            while (plugin->prev) {
                  if (plugin->src_frames)
                        frames = plugin->src_frames(plugin, frames);
                  snd_assert(frames > 0, return -ENXIO);
                  plugin = plugin->prev;
                  err = snd_pcm_plugin_alloc(plugin, frames);
                  if (err < 0)
                        return err;
            }
      }
      return 0;
}


snd_pcm_sframes_t snd_pcm_plugin_client_channels(struct snd_pcm_plugin *plugin,
                               snd_pcm_uframes_t frames,
                               struct snd_pcm_plugin_channel **channels)
{
      *channels = plugin->buf_channels;
      return frames;
}

int snd_pcm_plugin_build(struct snd_pcm_substream *plug,
                   const char *name,
                   struct snd_pcm_plugin_format *src_format,
                   struct snd_pcm_plugin_format *dst_format,
                   size_t extra,
                   struct snd_pcm_plugin **ret)
{
      struct snd_pcm_plugin *plugin;
      unsigned int channels;
      
      snd_assert(plug != NULL, return -ENXIO);
      snd_assert(src_format != NULL && dst_format != NULL, return -ENXIO);
      plugin = kzalloc(sizeof(*plugin) + extra, GFP_KERNEL);
      if (plugin == NULL)
            return -ENOMEM;
      plugin->name = name;
      plugin->plug = plug;
      plugin->stream = snd_pcm_plug_stream(plug);
      plugin->access = SNDRV_PCM_ACCESS_RW_INTERLEAVED;
      plugin->src_format = *src_format;
      plugin->src_width = snd_pcm_format_physical_width(src_format->format);
      snd_assert(plugin->src_width > 0, );
      plugin->dst_format = *dst_format;
      plugin->dst_width = snd_pcm_format_physical_width(dst_format->format);
      snd_assert(plugin->dst_width > 0, );
      if (plugin->stream == SNDRV_PCM_STREAM_PLAYBACK)
            channels = src_format->channels;
      else
            channels = dst_format->channels;
      plugin->buf_channels = kcalloc(channels, sizeof(*plugin->buf_channels), GFP_KERNEL);
      if (plugin->buf_channels == NULL) {
            snd_pcm_plugin_free(plugin);
            return -ENOMEM;
      }
      plugin->client_channels = snd_pcm_plugin_client_channels;
      *ret = plugin;
      return 0;
}

int snd_pcm_plugin_free(struct snd_pcm_plugin *plugin)
{
      if (! plugin)
            return 0;
      if (plugin->private_free)
            plugin->private_free(plugin);
      kfree(plugin->buf_channels);
      vfree(plugin->buf);
      kfree(plugin);
      return 0;
}

snd_pcm_sframes_t snd_pcm_plug_client_size(struct snd_pcm_substream *plug, snd_pcm_uframes_t drv_frames)
{
      struct snd_pcm_plugin *plugin, *plugin_prev, *plugin_next;
      int stream = snd_pcm_plug_stream(plug);

      snd_assert(plug != NULL, return -ENXIO);
      if (drv_frames == 0)
            return 0;
      if (stream == SNDRV_PCM_STREAM_PLAYBACK) {
            plugin = snd_pcm_plug_last(plug);
            while (plugin && drv_frames > 0) {
                  plugin_prev = plugin->prev;
                  if (plugin->src_frames)
                        drv_frames = plugin->src_frames(plugin, drv_frames);
                  plugin = plugin_prev;
            }
      } else if (stream == SNDRV_PCM_STREAM_CAPTURE) {
            plugin = snd_pcm_plug_first(plug);
            while (plugin && drv_frames > 0) {
                  plugin_next = plugin->next;
                  if (plugin->dst_frames)
                        drv_frames = plugin->dst_frames(plugin, drv_frames);
                  plugin = plugin_next;
            }
      } else
            snd_BUG();
      return drv_frames;
}

snd_pcm_sframes_t snd_pcm_plug_slave_size(struct snd_pcm_substream *plug, snd_pcm_uframes_t clt_frames)
{
      struct snd_pcm_plugin *plugin, *plugin_prev, *plugin_next;
      snd_pcm_sframes_t frames;
      int stream = snd_pcm_plug_stream(plug);
      
      snd_assert(plug != NULL, return -ENXIO);
      if (clt_frames == 0)
            return 0;
      frames = clt_frames;
      if (stream == SNDRV_PCM_STREAM_PLAYBACK) {
            plugin = snd_pcm_plug_first(plug);
            while (plugin && frames > 0) {
                  plugin_next = plugin->next;
                  if (plugin->dst_frames) {
                        frames = plugin->dst_frames(plugin, frames);
                        if (frames < 0)
                              return frames;
                  }
                  plugin = plugin_next;
            }
      } else if (stream == SNDRV_PCM_STREAM_CAPTURE) {
            plugin = snd_pcm_plug_last(plug);
            while (plugin) {
                  plugin_prev = plugin->prev;
                  if (plugin->src_frames) {
                        frames = plugin->src_frames(plugin, frames);
                        if (frames < 0)
                              return frames;
                  }
                  plugin = plugin_prev;
            }
      } else
            snd_BUG();
      return frames;
}

static int snd_pcm_plug_formats(struct snd_mask *mask, int format)
{
      struct snd_mask formats = *mask;
      u64 linfmts = (SNDRV_PCM_FMTBIT_U8 | SNDRV_PCM_FMTBIT_S8 |
                   SNDRV_PCM_FMTBIT_U16_LE | SNDRV_PCM_FMTBIT_S16_LE |
                   SNDRV_PCM_FMTBIT_U16_BE | SNDRV_PCM_FMTBIT_S16_BE |
                   SNDRV_PCM_FMTBIT_U24_LE | SNDRV_PCM_FMTBIT_S24_LE |
                   SNDRV_PCM_FMTBIT_U24_BE | SNDRV_PCM_FMTBIT_S24_BE |
                   SNDRV_PCM_FMTBIT_U24_3LE | SNDRV_PCM_FMTBIT_S24_3LE |
                   SNDRV_PCM_FMTBIT_U24_3BE | SNDRV_PCM_FMTBIT_S24_3BE |
                   SNDRV_PCM_FMTBIT_U32_LE | SNDRV_PCM_FMTBIT_S32_LE |
                   SNDRV_PCM_FMTBIT_U32_BE | SNDRV_PCM_FMTBIT_S32_BE);
      snd_mask_set(&formats, SNDRV_PCM_FORMAT_MU_LAW);
      
      if (formats.bits[0] & (u32)linfmts)
            formats.bits[0] |= (u32)linfmts;
      if (formats.bits[1] & (u32)(linfmts >> 32))
            formats.bits[1] |= (u32)(linfmts >> 32);
      return snd_mask_test(&formats, format);
}

static int preferred_formats[] = {
      SNDRV_PCM_FORMAT_S16_LE,
      SNDRV_PCM_FORMAT_S16_BE,
      SNDRV_PCM_FORMAT_U16_LE,
      SNDRV_PCM_FORMAT_U16_BE,
      SNDRV_PCM_FORMAT_S24_3LE,
      SNDRV_PCM_FORMAT_S24_3BE,
      SNDRV_PCM_FORMAT_U24_3LE,
      SNDRV_PCM_FORMAT_U24_3BE,
      SNDRV_PCM_FORMAT_S24_LE,
      SNDRV_PCM_FORMAT_S24_BE,
      SNDRV_PCM_FORMAT_U24_LE,
      SNDRV_PCM_FORMAT_U24_BE,
      SNDRV_PCM_FORMAT_S32_LE,
      SNDRV_PCM_FORMAT_S32_BE,
      SNDRV_PCM_FORMAT_U32_LE,
      SNDRV_PCM_FORMAT_U32_BE,
      SNDRV_PCM_FORMAT_S8,
      SNDRV_PCM_FORMAT_U8
};

int snd_pcm_plug_slave_format(int format, struct snd_mask *format_mask)
{
      int i;

      if (snd_mask_test(format_mask, format))
            return format;
      if (! snd_pcm_plug_formats(format_mask, format))
            return -EINVAL;
      if (snd_pcm_format_linear(format)) {
            unsigned int width = snd_pcm_format_width(format);
            int unsignd = snd_pcm_format_unsigned(format) > 0;
            int big = snd_pcm_format_big_endian(format) > 0;
            unsigned int badness, best = -1;
            int best_format = -1;
            for (i = 0; i < ARRAY_SIZE(preferred_formats); i++) {
                  int f = preferred_formats[i];
                  unsigned int w;
                  if (!snd_mask_test(format_mask, f))
                        continue;
                  w = snd_pcm_format_width(f);
                  if (w >= width)
                        badness = w - width;
                  else
                        badness = width - w + 32;
                  badness += snd_pcm_format_unsigned(f) != unsignd;
                  badness += snd_pcm_format_big_endian(f) != big;
                  if (badness < best) {
                        best_format = f;
                        best = badness;
                  }
            }
            return best_format >= 0 ? best_format : -EINVAL;
      } else {
            switch (format) {
            case SNDRV_PCM_FORMAT_MU_LAW:
                  for (i = 0; i < ARRAY_SIZE(preferred_formats); ++i) {
                        int format1 = preferred_formats[i];
                        if (snd_mask_test(format_mask, format1))
                              return format1;
                  }
            default:
                  return -EINVAL;
            }
      }
}

int snd_pcm_plug_format_plugins(struct snd_pcm_substream *plug,
                        struct snd_pcm_hw_params *params,
                        struct snd_pcm_hw_params *slave_params)
{
      struct snd_pcm_plugin_format tmpformat;
      struct snd_pcm_plugin_format dstformat;
      struct snd_pcm_plugin_format srcformat;
      int src_access, dst_access;
      struct snd_pcm_plugin *plugin = NULL;
      int err;
      int stream = snd_pcm_plug_stream(plug);
      int slave_interleaved = (params_channels(slave_params) == 1 ||
                         params_access(slave_params) == SNDRV_PCM_ACCESS_RW_INTERLEAVED);

      switch (stream) {
      case SNDRV_PCM_STREAM_PLAYBACK:
            dstformat.format = params_format(slave_params);
            dstformat.rate = params_rate(slave_params);
            dstformat.channels = params_channels(slave_params);
            srcformat.format = params_format(params);
            srcformat.rate = params_rate(params);
            srcformat.channels = params_channels(params);
            src_access = SNDRV_PCM_ACCESS_RW_INTERLEAVED;
            dst_access = (slave_interleaved ? SNDRV_PCM_ACCESS_RW_INTERLEAVED :
                                      SNDRV_PCM_ACCESS_RW_NONINTERLEAVED);
            break;
      case SNDRV_PCM_STREAM_CAPTURE:
            dstformat.format = params_format(params);
            dstformat.rate = params_rate(params);
            dstformat.channels = params_channels(params);
            srcformat.format = params_format(slave_params);
            srcformat.rate = params_rate(slave_params);
            srcformat.channels = params_channels(slave_params);
            src_access = (slave_interleaved ? SNDRV_PCM_ACCESS_RW_INTERLEAVED :
                                      SNDRV_PCM_ACCESS_RW_NONINTERLEAVED);
            dst_access = SNDRV_PCM_ACCESS_RW_INTERLEAVED;
            break;
      default:
            snd_BUG();
            return -EINVAL;
      }
      tmpformat = srcformat;
            
      pdprintf("srcformat: format=%i, rate=%i, channels=%i\n", 
             srcformat.format,
             srcformat.rate,
             srcformat.channels);
      pdprintf("dstformat: format=%i, rate=%i, channels=%i\n", 
             dstformat.format,
             dstformat.rate,
             dstformat.channels);

      /* Format change (linearization) */
      if (! rate_match(srcformat.rate, dstformat.rate) &&
          ! snd_pcm_format_linear(srcformat.format)) {
            if (srcformat.format != SNDRV_PCM_FORMAT_MU_LAW)
                  return -EINVAL;
            tmpformat.format = SNDRV_PCM_FORMAT_S16;
            err = snd_pcm_plugin_build_mulaw(plug,
                                     &srcformat, &tmpformat,
                                     &plugin);
            if (err < 0)
                  return err;
            err = snd_pcm_plugin_append(plugin);
            if (err < 0) {
                  snd_pcm_plugin_free(plugin);
                  return err;
            }
            srcformat = tmpformat;
            src_access = dst_access;
      }

      /* channels reduction */
      if (srcformat.channels > dstformat.channels) {
            tmpformat.channels = dstformat.channels;
            err = snd_pcm_plugin_build_route(plug, &srcformat, &tmpformat, &plugin);
            pdprintf("channels reduction: src=%i, dst=%i returns %i\n", srcformat.channels, tmpformat.channels, err);
            if (err < 0)
                  return err;
            err = snd_pcm_plugin_append(plugin);
            if (err < 0) {
                  snd_pcm_plugin_free(plugin);
                  return err;
            }
            srcformat = tmpformat;
            src_access = dst_access;
      }

      /* rate resampling */
      if (!rate_match(srcformat.rate, dstformat.rate)) {
            if (srcformat.format != SNDRV_PCM_FORMAT_S16) {
                  /* convert to S16 for resampling */
                  tmpformat.format = SNDRV_PCM_FORMAT_S16;
                  err = snd_pcm_plugin_build_linear(plug,
                                            &srcformat, &tmpformat,
                                            &plugin);
                  if (err < 0)
                        return err;
                  err = snd_pcm_plugin_append(plugin);
                  if (err < 0) {
                        snd_pcm_plugin_free(plugin);
                        return err;
                  }
                  srcformat = tmpformat;
                  src_access = dst_access;
            }
            tmpformat.rate = dstformat.rate;
            err = snd_pcm_plugin_build_rate(plug,
                                    &srcformat, &tmpformat,
                                    &plugin);
            pdprintf("rate down resampling: src=%i, dst=%i returns %i\n", srcformat.rate, tmpformat.rate, err);
            if (err < 0)
                  return err;
            err = snd_pcm_plugin_append(plugin);
            if (err < 0) {
                  snd_pcm_plugin_free(plugin);
                  return err;
            }
            srcformat = tmpformat;
            src_access = dst_access;
        }

      /* format change */
      if (srcformat.format != dstformat.format) {
            tmpformat.format = dstformat.format;
            if (srcformat.format == SNDRV_PCM_FORMAT_MU_LAW ||
                tmpformat.format == SNDRV_PCM_FORMAT_MU_LAW) {
                  err = snd_pcm_plugin_build_mulaw(plug,
                                           &srcformat, &tmpformat,
                                           &plugin);
            }
            else if (snd_pcm_format_linear(srcformat.format) &&
                   snd_pcm_format_linear(tmpformat.format)) {
                  err = snd_pcm_plugin_build_linear(plug,
                                            &srcformat, &tmpformat,
                                            &plugin);
            }
            else
                  return -EINVAL;
            pdprintf("format change: src=%i, dst=%i returns %i\n", srcformat.format, tmpformat.format, err);
            if (err < 0)
                  return err;
            err = snd_pcm_plugin_append(plugin);
            if (err < 0) {
                  snd_pcm_plugin_free(plugin);
                  return err;
            }
            srcformat = tmpformat;
            src_access = dst_access;
      }

      /* channels extension */
      if (srcformat.channels < dstformat.channels) {
            tmpformat.channels = dstformat.channels;
            err = snd_pcm_plugin_build_route(plug, &srcformat, &tmpformat, &plugin);
            pdprintf("channels extension: src=%i, dst=%i returns %i\n", srcformat.channels, tmpformat.channels, err);
            if (err < 0)
                  return err;
            err = snd_pcm_plugin_append(plugin);
            if (err < 0) {
                  snd_pcm_plugin_free(plugin);
                  return err;
            }
            srcformat = tmpformat;
            src_access = dst_access;
      }

      /* de-interleave */
      if (src_access != dst_access) {
            err = snd_pcm_plugin_build_copy(plug,
                                    &srcformat,
                                    &tmpformat,
                                    &plugin);
            pdprintf("interleave change (copy: returns %i)\n", err);
            if (err < 0)
                  return err;
            err = snd_pcm_plugin_append(plugin);
            if (err < 0) {
                  snd_pcm_plugin_free(plugin);
                  return err;
            }
      }

      return 0;
}

snd_pcm_sframes_t snd_pcm_plug_client_channels_buf(struct snd_pcm_substream *plug,
                               char *buf,
                               snd_pcm_uframes_t count,
                               struct snd_pcm_plugin_channel **channels)
{
      struct snd_pcm_plugin *plugin;
      struct snd_pcm_plugin_channel *v;
      struct snd_pcm_plugin_format *format;
      int width, nchannels, channel;
      int stream = snd_pcm_plug_stream(plug);

      snd_assert(buf != NULL, return -ENXIO);
      if (stream == SNDRV_PCM_STREAM_PLAYBACK) {
            plugin = snd_pcm_plug_first(plug);
            format = &plugin->src_format;
      } else {
            plugin = snd_pcm_plug_last(plug);
            format = &plugin->dst_format;
      }
      v = plugin->buf_channels;
      *channels = v;
      if ((width = snd_pcm_format_physical_width(format->format)) < 0)
            return width;
      nchannels = format->channels;
      snd_assert(plugin->access == SNDRV_PCM_ACCESS_RW_INTERLEAVED || format->channels <= 1, return -ENXIO);
      for (channel = 0; channel < nchannels; channel++, v++) {
            v->frames = count;
            v->enabled = 1;
            v->wanted = (stream == SNDRV_PCM_STREAM_CAPTURE);
            v->area.addr = buf;
            v->area.first = channel * width;
            v->area.step = nchannels * width;
      }
      return count;
}

snd_pcm_sframes_t snd_pcm_plug_write_transfer(struct snd_pcm_substream *plug, struct snd_pcm_plugin_channel *src_channels, snd_pcm_uframes_t size)
{
      struct snd_pcm_plugin *plugin, *next;
      struct snd_pcm_plugin_channel *dst_channels;
      int err;
      snd_pcm_sframes_t frames = size;

      plugin = snd_pcm_plug_first(plug);
      while (plugin && frames > 0) {
            if ((next = plugin->next) != NULL) {
                  snd_pcm_sframes_t frames1 = frames;
                  if (plugin->dst_frames)
                        frames1 = plugin->dst_frames(plugin, frames);
                  if ((err = next->client_channels(next, frames1, &dst_channels)) < 0) {
                        return err;
                  }
                  if (err != frames1) {
                        frames = err;
                        if (plugin->src_frames)
                              frames = plugin->src_frames(plugin, frames1);
                  }
            } else
                  dst_channels = NULL;
            pdprintf("write plugin: %s, %li\n", plugin->name, frames);
            if ((frames = plugin->transfer(plugin, src_channels, dst_channels, frames)) < 0)
                  return frames;
            src_channels = dst_channels;
            plugin = next;
      }
      return snd_pcm_plug_client_size(plug, frames);
}

snd_pcm_sframes_t snd_pcm_plug_read_transfer(struct snd_pcm_substream *plug, struct snd_pcm_plugin_channel *dst_channels_final, snd_pcm_uframes_t size)
{
      struct snd_pcm_plugin *plugin, *next;
      struct snd_pcm_plugin_channel *src_channels, *dst_channels;
      snd_pcm_sframes_t frames = size;
      int err;

      frames = snd_pcm_plug_slave_size(plug, frames);
      if (frames < 0)
            return frames;

      src_channels = NULL;
      plugin = snd_pcm_plug_first(plug);
      while (plugin && frames > 0) {
            if ((next = plugin->next) != NULL) {
                  if ((err = plugin->client_channels(plugin, frames, &dst_channels)) < 0) {
                        return err;
                  }
                  frames = err;
            } else {
                  dst_channels = dst_channels_final;
            }
            pdprintf("read plugin: %s, %li\n", plugin->name, frames);
            if ((frames = plugin->transfer(plugin, src_channels, dst_channels, frames)) < 0)
                  return frames;
            plugin = next;
            src_channels = dst_channels;
      }
      return frames;
}

int snd_pcm_area_silence(const struct snd_pcm_channel_area *dst_area, size_t dst_offset,
                   size_t samples, int format)
{
      /* FIXME: sub byte resolution and odd dst_offset */
      unsigned char *dst;
      unsigned int dst_step;
      int width;
      const unsigned char *silence;
      if (!dst_area->addr)
            return 0;
      dst = dst_area->addr + (dst_area->first + dst_area->step * dst_offset) / 8;
      width = snd_pcm_format_physical_width(format);
      if (width <= 0)
            return -EINVAL;
      if (dst_area->step == (unsigned int) width && width >= 8)
            return snd_pcm_format_set_silence(format, dst, samples);
      silence = snd_pcm_format_silence_64(format);
      if (! silence)
            return -EINVAL;
      dst_step = dst_area->step / 8;
      if (width == 4) {
            /* Ima ADPCM */
            int dstbit = dst_area->first % 8;
            int dstbit_step = dst_area->step % 8;
            while (samples-- > 0) {
                  if (dstbit)
                        *dst &= 0xf0;
                  else
                        *dst &= 0x0f;
                  dst += dst_step;
                  dstbit += dstbit_step;
                  if (dstbit == 8) {
                        dst++;
                        dstbit = 0;
                  }
            }
      } else {
            width /= 8;
            while (samples-- > 0) {
                  memcpy(dst, silence, width);
                  dst += dst_step;
            }
      }
      return 0;
}

int snd_pcm_area_copy(const struct snd_pcm_channel_area *src_area, size_t src_offset,
                  const struct snd_pcm_channel_area *dst_area, size_t dst_offset,
                  size_t samples, int format)
{
      /* FIXME: sub byte resolution and odd dst_offset */
      char *src, *dst;
      int width;
      int src_step, dst_step;
      src = src_area->addr + (src_area->first + src_area->step * src_offset) / 8;
      if (!src_area->addr)
            return snd_pcm_area_silence(dst_area, dst_offset, samples, format);
      dst = dst_area->addr + (dst_area->first + dst_area->step * dst_offset) / 8;
      if (!dst_area->addr)
            return 0;
      width = snd_pcm_format_physical_width(format);
      if (width <= 0)
            return -EINVAL;
      if (src_area->step == (unsigned int) width &&
          dst_area->step == (unsigned int) width && width >= 8) {
            size_t bytes = samples * width / 8;
            memcpy(dst, src, bytes);
            return 0;
      }
      src_step = src_area->step / 8;
      dst_step = dst_area->step / 8;
      if (width == 4) {
            /* Ima ADPCM */
            int srcbit = src_area->first % 8;
            int srcbit_step = src_area->step % 8;
            int dstbit = dst_area->first % 8;
            int dstbit_step = dst_area->step % 8;
            while (samples-- > 0) {
                  unsigned char srcval;
                  if (srcbit)
                        srcval = *src & 0x0f;
                  else
                        srcval = (*src & 0xf0) >> 4;
                  if (dstbit)
                        *dst = (*dst & 0xf0) | srcval;
                  else
                        *dst = (*dst & 0x0f) | (srcval << 4);
                  src += src_step;
                  srcbit += srcbit_step;
                  if (srcbit == 8) {
                        src++;
                        srcbit = 0;
                  }
                  dst += dst_step;
                  dstbit += dstbit_step;
                  if (dstbit == 8) {
                        dst++;
                        dstbit = 0;
                  }
            }
      } else {
            width /= 8;
            while (samples-- > 0) {
                  memcpy(dst, src, width);
                  src += src_step;
                  dst += dst_step;
            }
      }
      return 0;
}

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