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pcm_softvol.c

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/**
 * \file pcm/pcm_softvol.c
 * \ingroup PCM_Plugins
 * \brief PCM Soft Volume Plugin Interface
 * \author Takashi Iwai <tiwai@suse.de>
 * \date 2004
 */
/*
 *  PCM - Soft Volume Plugin
 *  Copyright (c) 2004 by Takashi Iwai <tiwai@suse.de>
 *
 *
 *   This library is free software; you can redistribute it and/or modify
 *   it under the terms of the GNU Lesser General Public License as
 *   published by the Free Software Foundation; either version 2.1 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 Lesser General Public License for more details.
 *
 *   You should have received a copy of the GNU Lesser 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 <byteswap.h>
#include <math.h>
#include "pcm_local.h"
#include "pcm_plugin.h"

#ifndef PIC
/* entry for static linking */
const char *_snd_module_pcm_softvol = "";
#endif

#ifndef DOC_HIDDEN

00041 typedef struct {
      /* This field need to be the first */
      snd_pcm_plugin_t plug;
      snd_pcm_format_t sformat;
      unsigned int cchannels;
      snd_ctl_t *ctl;
      snd_ctl_elem_value_t elem;
      unsigned int cur_vol[2];
      unsigned int max_val;
      double min_dB;
      unsigned short *dB_value;
} snd_pcm_softvol_t;

#define VOL_SCALE_SHIFT       16

#define PRESET_RESOLUTION     256
#define PRESET_MIN_DB         -48.0

static unsigned short preset_dB_value[PRESET_RESOLUTION] = {
      0x0000, 0x0104, 0x010a, 0x0110, 0x0116, 0x011c, 0x0122, 0x0129,
      0x012f, 0x0136, 0x013d, 0x0144, 0x014b, 0x0152, 0x015a, 0x0161,
      0x0169, 0x0171, 0x0179, 0x0181, 0x018a, 0x0193, 0x019c, 0x01a5,
      0x01ae, 0x01b7, 0x01c1, 0x01cb, 0x01d5, 0x01df, 0x01ea, 0x01f5,
      0x0200, 0x020b, 0x0216, 0x0222, 0x022e, 0x023b, 0x0247, 0x0254,
      0x0261, 0x026e, 0x027c, 0x028a, 0x0298, 0x02a7, 0x02b6, 0x02c5,
      0x02d5, 0x02e5, 0x02f5, 0x0306, 0x0317, 0x0328, 0x033a, 0x034c,
      0x035f, 0x0372, 0x0385, 0x0399, 0x03ad, 0x03c2, 0x03d7, 0x03ed,
      0x0403, 0x041a, 0x0431, 0x0448, 0x0460, 0x0479, 0x0492, 0x04ac,
      0x04c6, 0x04e1, 0x04fd, 0x0519, 0x0535, 0x0553, 0x0571, 0x058f,
      0x05af, 0x05cf, 0x05ef, 0x0611, 0x0633, 0x0656, 0x067a, 0x069e,
      0x06c3, 0x06ea, 0x0710, 0x0738, 0x0761, 0x078a, 0x07b5, 0x07e0,
      0x080d, 0x083a, 0x0868, 0x0898, 0x08c8, 0x08fa, 0x092c, 0x0960,
      0x0995, 0x09cb, 0x0a02, 0x0a3a, 0x0a74, 0x0aae, 0x0aeb, 0x0b28,
      0x0b67, 0x0ba7, 0x0be9, 0x0c2c, 0x0c70, 0x0cb6, 0x0cfe, 0x0d47,
      0x0d92, 0x0dde, 0x0e2d, 0x0e7c, 0x0ece, 0x0f21, 0x0f76, 0x0fce,
      0x1027, 0x1081, 0x10de, 0x113d, 0x119f, 0x1202, 0x1267, 0x12cf,
      0x1339, 0x13a5, 0x1414, 0x1485, 0x14f8, 0x156e, 0x15e7, 0x1662,
      0x16e0, 0x1761, 0x17e5, 0x186b, 0x18f5, 0x1981, 0x1a11, 0x1aa4,
      0x1b3a, 0x1bd3, 0x1c70, 0x1d10, 0x1db4, 0x1e5b, 0x1f06, 0x1fb4,
      0x2067, 0x211d, 0x21d8, 0x2297, 0x2359, 0x2420, 0x24ec, 0x25bc,
      0x2690, 0x2769, 0x2847, 0x292a, 0x2a12, 0x2aff, 0x2bf1, 0x2ce8,
      0x2de5, 0x2ee8, 0x2ff0, 0x30fe, 0x3211, 0x332b, 0x344c, 0x3572,
      0x369f, 0x37d2, 0x390d, 0x3a4e, 0x3b96, 0x3ce6, 0x3e3d, 0x3f9b,
      0x4101, 0x426f, 0x43e6, 0x4564, 0x46eb, 0x487a, 0x4a12, 0x4bb3,
      0x4d5d, 0x4f11, 0x50ce, 0x5295, 0x5466, 0x5642, 0x5827, 0x5a18,
      0x5c13, 0x5e19, 0x602b, 0x6249, 0x6472, 0x66a8, 0x68ea, 0x6b39,
      0x6d94, 0x6ffd, 0x7274, 0x74f8, 0x778b, 0x7a2c, 0x7cdc, 0x7f9b,
      0x826a, 0x8548, 0x8836, 0x8b35, 0x8e45, 0x9166, 0x9499, 0x97de,
      0x9b35, 0x9e9f, 0xa21c, 0xa5ad, 0xa952, 0xad0b, 0xb0da, 0xb4bd,
      0xb8b7, 0xbcc7, 0xc0ee, 0xc52d, 0xc983, 0xcdf1, 0xd279, 0xd71a,
      0xdbd5, 0xe0ab, 0xe59c, 0xeaa9, 0xefd3, 0xf519, 0xfa7d, 0xffff,
};

/* (32bit x 16bit) >> 16 */
00095 typedef union {
      int i;
      short s[2];
} val_t;
static inline int MULTI_DIV_int(int a, unsigned short b)
{
      val_t v, x, y;
      v.i = a;
      y.i = 0;
#if __BYTE_ORDER == __LITTLE_ENDIAN
      x.i = (unsigned int)v.s[0] * b;
      y.s[0] = x.s[1];
      y.i += (int)v.s[1] * b;
#else
      x.i = (unsigned int)v.s[1] * b;
      y.s[1] = x.s[0];
      y.i += (int)v.s[0] * b;
#endif
      return y.i;
}

/* (16bit x 16bit) >> 16 */
#define MULTI_DIV_short(src,scale) (((int)(src) * (scale)) >> VOL_SCALE_SHIFT)

#endif /* DOC_HIDDEN */

/*
 * apply volumue attenuation
 *
 * TODO: use SIMD operations
 */

#ifndef DOC_HIDDEN
#define CONVERT_AREA(TYPE) do {     \
      unsigned int ch, fr; \
      TYPE *src, *dst; \
      for (ch = 0; ch < channels; ch++) { \
            src_area = &src_areas[ch]; \
            dst_area = &dst_areas[ch]; \
            src = snd_pcm_channel_area_addr(src_area, src_offset); \
            dst = snd_pcm_channel_area_addr(dst_area, dst_offset); \
            src_step = snd_pcm_channel_area_step(src_area) / sizeof(TYPE); \
            dst_step = snd_pcm_channel_area_step(dst_area) / sizeof(TYPE); \
            GET_VOL_SCALE; \
            fr = frames; \
            if (! vol_scale) { \
                  while (fr--) { \
                        *dst = 0; \
                        dst += dst_step; \
                  } \
            } else if (vol_scale == 0xffff) { \
                  while (fr--) { \
                        *dst = *src; \
                        src += src_step; \
                        dst += dst_step; \
                  } \
            } else { \
                  while (fr--) { \
                        *dst = MULTI_DIV_##TYPE(*src, vol_scale);\
                        src += src_step; \
                        dst += dst_step; \
                  } \
            } \
      } \
} while (0)
      

            
#define GET_VOL_SCALE \
      switch (ch) { \
      case 0: \
      case 2: \
            vol_scale = (channels == ch + 1) ? vol_c : vol[0]; \
            break; \
      case 4: \
      case 5: \
            vol_scale = vol_c; \
            break; \
      default: \
            vol_scale = vol[ch & 1]; \
            break; \
      }

#endif /* DOC_HIDDEN */

/* 2-channel stereo control */
static void softvol_convert_stereo_vol(snd_pcm_softvol_t *svol,
                               const snd_pcm_channel_area_t *dst_areas,
                               snd_pcm_uframes_t dst_offset,
                               const snd_pcm_channel_area_t *src_areas,
                               snd_pcm_uframes_t src_offset,
                               unsigned int channels,
                               snd_pcm_uframes_t frames)
{
      const snd_pcm_channel_area_t *dst_area, *src_area;
      unsigned int src_step, dst_step;
      unsigned int vol_scale, vol[2], vol_c;

      if (svol->cur_vol[0] == 0 && svol->cur_vol[1] == 0) {
            snd_pcm_areas_silence(dst_areas, dst_offset, channels, frames,
                              svol->sformat);
            return;
      } else if (svol->cur_vol[0] == svol->max_val &&
               svol->cur_vol[1] == svol->max_val) {
            snd_pcm_areas_copy(dst_areas, dst_offset, src_areas, src_offset,
                           channels, frames, svol->sformat);
            return;
      }

      vol[0] = svol->dB_value[svol->cur_vol[0]];
      vol[1] = svol->dB_value[svol->cur_vol[1]];
      vol_c = svol->dB_value[(svol->cur_vol[0] + svol->cur_vol[1]) / 2];
      if (svol->sformat == SND_PCM_FORMAT_S16) {
            /* 16bit samples */
            CONVERT_AREA(short);
      } else {
            /* 32bit samples */
            CONVERT_AREA(int);
      }
}

#undef GET_VOL_SCALE
#define GET_VOL_SCALE

/* mono control */
static void softvol_convert_mono_vol(snd_pcm_softvol_t *svol,
                             const snd_pcm_channel_area_t *dst_areas,
                             snd_pcm_uframes_t dst_offset,
                             const snd_pcm_channel_area_t *src_areas,
                             snd_pcm_uframes_t src_offset,
                             unsigned int channels,
                             snd_pcm_uframes_t frames)
{
      const snd_pcm_channel_area_t *dst_area, *src_area;
      unsigned int src_step, dst_step;
      unsigned int vol_scale;

      if (svol->cur_vol[0] == 0) {
            snd_pcm_areas_silence(dst_areas, dst_offset, channels, frames,
                              svol->sformat);
            return;
      } else if (svol->cur_vol[0] == svol->max_val) {
            snd_pcm_areas_copy(dst_areas, dst_offset, src_areas, src_offset,
                           channels, frames, svol->sformat);
            return;
      }

      vol_scale = svol->dB_value[svol->cur_vol[0]];
      if (svol->sformat == SND_PCM_FORMAT_S16) {
            /* 16bit samples */
            CONVERT_AREA(short);
      } else {
            /* 32bit samples */
            CONVERT_AREA(int);
      }
}

/*
 * get the current volume value from driver
 *
 * TODO: mmap support?
 */
static void get_current_volume(snd_pcm_softvol_t *svol)
{
      unsigned int val;
      unsigned int i;

      if (snd_ctl_elem_read(svol->ctl, &svol->elem) < 0)
            return;
      for (i = 0; i < svol->cchannels; i++) {
            val = svol->elem.value.integer.value[i];
            if (val > svol->max_val)
                  val = svol->max_val;
            svol->cur_vol[i] = val;
      }
}

static void softvol_free(snd_pcm_softvol_t *svol)
{
      if (svol->plug.gen.close_slave)
            snd_pcm_close(svol->plug.gen.slave);
      if (svol->ctl)
            snd_ctl_close(svol->ctl);
      if (svol->dB_value && svol->dB_value != preset_dB_value)
            free(svol->dB_value);
      free(svol);
}

static int snd_pcm_softvol_close(snd_pcm_t *pcm)
{
      snd_pcm_softvol_t *svol = pcm->private_data;
      softvol_free(svol);
      return 0;
}

static int snd_pcm_softvol_hw_refine_cprepare(snd_pcm_t *pcm ATTRIBUTE_UNUSED,
                                    snd_pcm_hw_params_t *params)
{
      int err;
      snd_pcm_access_mask_t access_mask = { SND_PCM_ACCBIT_SHM };
      snd_pcm_format_mask_t format_mask = {
            { (1U << SND_PCM_FORMAT_S16) | (1U << SND_PCM_FORMAT_S32) }
      };
      err = _snd_pcm_hw_param_set_mask(params, SND_PCM_HW_PARAM_ACCESS,
                               &access_mask);
      if (err < 0)
            return err;
      err = _snd_pcm_hw_param_set_mask(params, SND_PCM_HW_PARAM_FORMAT,
                               &format_mask);
      if (err < 0)
            return err;
      err = _snd_pcm_hw_params_set_subformat(params, SND_PCM_SUBFORMAT_STD);
      if (err < 0)
            return err;
      err = _snd_pcm_hw_param_set_min(params, SND_PCM_HW_PARAM_CHANNELS, 1, 0);
      if (err < 0)
            return err;
      params->info &= ~(SND_PCM_INFO_MMAP | SND_PCM_INFO_MMAP_VALID);
      return 0;
}

static int snd_pcm_softvol_hw_refine_sprepare(snd_pcm_t *pcm, snd_pcm_hw_params_t *sparams)
{
      snd_pcm_softvol_t *svol = pcm->private_data;
      snd_pcm_access_mask_t saccess_mask = { SND_PCM_ACCBIT_MMAP };
      _snd_pcm_hw_params_any(sparams);
      _snd_pcm_hw_param_set_mask(sparams, SND_PCM_HW_PARAM_ACCESS,
                           &saccess_mask);
      if (svol->sformat != SND_PCM_FORMAT_UNKNOWN) {
            _snd_pcm_hw_params_set_format(sparams, svol->sformat);
            _snd_pcm_hw_params_set_subformat(sparams, SND_PCM_SUBFORMAT_STD);
      }
      return 0;
}

static int snd_pcm_softvol_hw_refine_schange(snd_pcm_t *pcm,
                                   snd_pcm_hw_params_t *params,
                                   snd_pcm_hw_params_t *sparams)
{
      snd_pcm_softvol_t *svol = pcm->private_data;
      int err;
      unsigned int links = (SND_PCM_HW_PARBIT_CHANNELS |
                        SND_PCM_HW_PARBIT_RATE |
                        SND_PCM_HW_PARBIT_PERIODS |
                        SND_PCM_HW_PARBIT_PERIOD_SIZE |
                        SND_PCM_HW_PARBIT_PERIOD_TIME |
                        SND_PCM_HW_PARBIT_BUFFER_SIZE |
                        SND_PCM_HW_PARBIT_BUFFER_TIME |
                        SND_PCM_HW_PARBIT_TICK_TIME);
      if (svol->sformat == SND_PCM_FORMAT_UNKNOWN)
            links |= (SND_PCM_HW_PARBIT_FORMAT | 
                    SND_PCM_HW_PARBIT_SUBFORMAT |
                    SND_PCM_HW_PARBIT_SAMPLE_BITS);
      err = _snd_pcm_hw_params_refine(sparams, links, params);
      if (err < 0)
            return err;
      return 0;
}
      
static int snd_pcm_softvol_hw_refine_cchange(snd_pcm_t *pcm,
                                   snd_pcm_hw_params_t *params,
                                  snd_pcm_hw_params_t *sparams)
{
      snd_pcm_softvol_t *svol = pcm->private_data;
      int err;
      unsigned int links = (SND_PCM_HW_PARBIT_CHANNELS |
                        SND_PCM_HW_PARBIT_RATE |
                        SND_PCM_HW_PARBIT_PERIODS |
                        SND_PCM_HW_PARBIT_PERIOD_SIZE |
                        SND_PCM_HW_PARBIT_PERIOD_TIME |
                        SND_PCM_HW_PARBIT_BUFFER_SIZE |
                        SND_PCM_HW_PARBIT_BUFFER_TIME |
                        SND_PCM_HW_PARBIT_TICK_TIME);
      if (svol->sformat == SND_PCM_FORMAT_UNKNOWN)
            links |= (SND_PCM_HW_PARBIT_FORMAT | 
                    SND_PCM_HW_PARBIT_SUBFORMAT |
                    SND_PCM_HW_PARBIT_SAMPLE_BITS);
      err = _snd_pcm_hw_params_refine(params, links, sparams);
      if (err < 0)
            return err;
      return 0;
}

static int snd_pcm_softvol_hw_refine(snd_pcm_t *pcm, snd_pcm_hw_params_t *params)
{
      return snd_pcm_hw_refine_slave(pcm, params,
                               snd_pcm_softvol_hw_refine_cprepare,
                               snd_pcm_softvol_hw_refine_cchange,
                               snd_pcm_softvol_hw_refine_sprepare,
                               snd_pcm_softvol_hw_refine_schange,
                               snd_pcm_generic_hw_refine);
}

static int snd_pcm_softvol_hw_params(snd_pcm_t *pcm, snd_pcm_hw_params_t * params)
{
      snd_pcm_softvol_t *svol = pcm->private_data;
      snd_pcm_t *slave = svol->plug.gen.slave;
      int err = snd_pcm_hw_params_slave(pcm, params,
                                snd_pcm_softvol_hw_refine_cchange,
                                snd_pcm_softvol_hw_refine_sprepare,
                                snd_pcm_softvol_hw_refine_schange,
                                snd_pcm_generic_hw_params);
      if (err < 0)
            return err;
      if (slave->format != SND_PCM_FORMAT_S16 &&
          slave->format != SND_PCM_FORMAT_S32) {
            SNDERR("softvol supports only S16 or S32");
            return -EINVAL;
      }
      svol->sformat = slave->format;
      return 0;
}

static snd_pcm_uframes_t
snd_pcm_softvol_write_areas(snd_pcm_t *pcm,
                      const snd_pcm_channel_area_t *areas,
                      snd_pcm_uframes_t offset,
                      snd_pcm_uframes_t size,
                      const snd_pcm_channel_area_t *slave_areas,
                      snd_pcm_uframes_t slave_offset,
                      snd_pcm_uframes_t *slave_sizep)
{
      snd_pcm_softvol_t *svol = pcm->private_data;
      if (size > *slave_sizep)
            size = *slave_sizep;
      get_current_volume(svol);
      if (svol->cchannels == 1)
            softvol_convert_mono_vol(svol, slave_areas, slave_offset,
                               areas, offset, pcm->channels, size);
      else
            softvol_convert_stereo_vol(svol, slave_areas, slave_offset,
                                 areas, offset, pcm->channels, size);
      *slave_sizep = size;
      return size;
}

static snd_pcm_uframes_t
snd_pcm_softvol_read_areas(snd_pcm_t *pcm,
                     const snd_pcm_channel_area_t *areas,
                     snd_pcm_uframes_t offset,
                     snd_pcm_uframes_t size,
                     const snd_pcm_channel_area_t *slave_areas,
                     snd_pcm_uframes_t slave_offset,
                     snd_pcm_uframes_t *slave_sizep)
{
      snd_pcm_softvol_t *svol = pcm->private_data;
      if (size > *slave_sizep)
            size = *slave_sizep;
      get_current_volume(svol);
      if (svol->cchannels == 1)
            softvol_convert_mono_vol(svol, areas, offset, slave_areas,
                               slave_offset, pcm->channels, size);
      else
            softvol_convert_stereo_vol(svol, areas, offset, slave_areas,
                                 slave_offset, pcm->channels, size);
      *slave_sizep = size;
      return size;
}

static void snd_pcm_softvol_dump(snd_pcm_t *pcm, snd_output_t *out)
{
      snd_pcm_softvol_t *svol = pcm->private_data;
      snd_output_printf(out, "Soft volume PCM\n");
      snd_output_printf(out, "Control: %s\n", svol->elem.id.name);
      snd_output_printf(out, "min_dB: %g\n", svol->min_dB);
      snd_output_printf(out, "resolution: %d\n", svol->max_val + 1);
      if (pcm->setup) {
            snd_output_printf(out, "Its setup is:\n");
            snd_pcm_dump_setup(pcm, out);
      }
      snd_output_printf(out, "Slave: ");
      snd_pcm_dump(svol->plug.gen.slave, out);
}

static int add_user_ctl(snd_pcm_softvol_t *svol, snd_ctl_elem_info_t *cinfo, int count)
{
      int err;
      int i;

      err = snd_ctl_elem_add_integer(svol->ctl, &cinfo->id, count, 0, svol->max_val, 0);
      if (err < 0)
            return err;
      /* set max value as default */
      for (i = 0; i < count; i++)
            svol->elem.value.integer.value[i] = svol->max_val;
      return snd_ctl_elem_write(svol->ctl, &svol->elem);
}

/*
 * load and set up user-control
 * returns 0 if the user-control is found or created,
 * returns 1 if the control is a hw control,
 * or a negative error code
 */
static int softvol_load_control(snd_pcm_t *pcm, snd_pcm_softvol_t *svol,
                        int ctl_card, snd_ctl_elem_id_t *ctl_id,
                        int cchannels, double min_dB, int resolution)
{
      char tmp_name[32];
      snd_pcm_info_t *info;
      snd_ctl_elem_info_t *cinfo;
      int err;
      unsigned int i;

      if (ctl_card < 0) {
            snd_pcm_info_alloca(&info);
            err = snd_pcm_info(pcm, info);
            if (err < 0)
                  return err;
            ctl_card = snd_pcm_info_get_card(info);
            if (ctl_card < 0) {
                  SNDERR("No card defined for softvol control");
                  return -EINVAL;
            }
      }
      sprintf(tmp_name, "hw:%d", ctl_card);
      err = snd_ctl_open(&svol->ctl, tmp_name, 0);
      if (err < 0) {
            SNDERR("Cannot open CTL %s", tmp_name);
            return err;
      }

      svol->elem.id = *ctl_id;
      svol->max_val = resolution - 1;
      svol->min_dB = min_dB;

      snd_ctl_elem_info_alloca(&cinfo);
      snd_ctl_elem_info_set_id(cinfo, ctl_id);
      if ((err = snd_ctl_elem_info(svol->ctl, cinfo)) < 0) {
            if (err != -ENOENT) {
                  SNDERR("Cannot get info for CTL %s", tmp_name);
                  return err;
            }
            err = add_user_ctl(svol, cinfo, cchannels);
            if (err < 0) {
                  SNDERR("Cannot add a control");
                  return err;
            }
      } else {
            if (! (cinfo->access & SNDRV_CTL_ELEM_ACCESS_USER)) {
                  /* hardware control exists */
                  return 1; /* notify */

            } else if (cinfo->type != SND_CTL_ELEM_TYPE_INTEGER ||
                     cinfo->count != (unsigned int)cchannels ||
                     cinfo->value.integer.min != 0 ||
                     cinfo->value.integer.max != resolution - 1) {
                  if ((err = snd_ctl_elem_remove(svol->ctl, &cinfo->id)) < 0) {
                        SNDERR("Control %s mismatch", tmp_name);
                        return err;
                  }
                  snd_ctl_elem_info_set_id(cinfo, ctl_id); /* reset numid */
                  if ((err = add_user_ctl(svol, cinfo, cchannels)) < 0) {
                        SNDERR("Cannot add a control");
                        return err;
                  }
            }
      }

      if (min_dB == PRESET_MIN_DB && resolution == PRESET_RESOLUTION)
            svol->dB_value = preset_dB_value;
      else {
#ifndef HAVE_SOFT_FLOAT
            svol->dB_value = calloc(resolution, sizeof(unsigned short));
            if (! svol->dB_value) {
                  SNDERR("cannot allocate dB table");
                  return -ENOMEM;
            }
            svol->min_dB = min_dB;
            for (i = 1; i < svol->max_val; i++) {
                  double db = svol->min_dB - ((i - 1) * svol->min_dB) / (svol->max_val - 1);
                  double v = (pow(10.0, db / 20.0) * (double)(1 << VOL_SCALE_SHIFT));
                  svol->dB_value[i] = (unsigned short)v;
            }
            svol->dB_value[svol->max_val] = 65535;
#else
            SNDERR("Cannot handle the given min_dB and resolution");
            return -EINVAL;
#endif
      }
      return 0;
}

static snd_pcm_ops_t snd_pcm_softvol_ops = {
      .close = snd_pcm_softvol_close,
      .info = snd_pcm_generic_info,
      .hw_refine = snd_pcm_softvol_hw_refine,
      .hw_params = snd_pcm_softvol_hw_params,
      .hw_free = snd_pcm_generic_hw_free,
      .sw_params = snd_pcm_generic_sw_params,
      .channel_info = snd_pcm_generic_channel_info,
      .dump = snd_pcm_softvol_dump,
      .nonblock = snd_pcm_generic_nonblock,
      .async = snd_pcm_generic_async,
      .mmap = snd_pcm_generic_mmap,
      .munmap = snd_pcm_generic_munmap,
};

/**
 * \brief Creates a new SoftVolume PCM
 * \param pcmp Returns created PCM handle
 * \param name Name of PCM
 * \param sformat Slave format
 * \param ctl_card card index of the control
 * \param ctl_id The control element
 * \param cchannels PCM channels
 * \param min_dB minimal dB value
 * \param resolution resolution of control
 * \param slave Slave PCM handle
 * \param close_slave When set, the slave PCM handle is closed with copy PCM
 * \retval zero on success otherwise a negative error code
 * \warning Using of this function might be dangerous in the sense
 *          of compatibility reasons. The prototype might be freely
 *          changed in future.
 */
00610 int snd_pcm_softvol_open(snd_pcm_t **pcmp, const char *name,
                   snd_pcm_format_t sformat,
                   int ctl_card, snd_ctl_elem_id_t *ctl_id,
                   int cchannels,
                   double min_dB, int resolution,
                   snd_pcm_t *slave, int close_slave)
{
      snd_pcm_t *pcm;
      snd_pcm_softvol_t *svol;
      int err;
      assert(pcmp && slave);
      if (sformat != SND_PCM_FORMAT_UNKNOWN &&
          sformat != SND_PCM_FORMAT_S16 &&
          sformat != SND_PCM_FORMAT_S32)
            return -EINVAL;
      svol = calloc(1, sizeof(*svol));
      if (! svol)
            return -ENOMEM;
      err = softvol_load_control(slave, svol, ctl_card, ctl_id, cchannels,
                           min_dB, resolution);
      if (err < 0) {
            softvol_free(svol);
            return err;
      }
      if (err > 0) { /* hardware control - no need for softvol! */
            softvol_free(svol);
            *pcmp = slave; /* just pass the slave */
            return 0;
      }

      /* do softvol */
      snd_pcm_plugin_init(&svol->plug);
      svol->sformat = sformat;
      svol->cchannels = cchannels;
      svol->plug.read = snd_pcm_softvol_read_areas;
      svol->plug.write = snd_pcm_softvol_write_areas;
      svol->plug.undo_read = snd_pcm_plugin_undo_read_generic;
      svol->plug.undo_write = snd_pcm_plugin_undo_write_generic;
      svol->plug.gen.slave = slave;
      svol->plug.gen.close_slave = close_slave;

      err = snd_pcm_new(&pcm, SND_PCM_TYPE_SOFTVOL, name, slave->stream, slave->mode);
      if (err < 0) {
            softvol_free(svol);
            return err;
      }
      pcm->ops = &snd_pcm_softvol_ops;
      pcm->fast_ops = &snd_pcm_plugin_fast_ops;
      pcm->private_data = svol;
      pcm->poll_fd = slave->poll_fd;
      pcm->poll_events = slave->poll_events;
      /*
       * Since the softvol converts on the place, and the format/channels
       * must be identical between source and destination, we don't need
       * an extra buffer.
       */
      pcm->mmap_shadow = 1;
      snd_pcm_set_hw_ptr(pcm, &svol->plug.hw_ptr, -1, 0);
      snd_pcm_set_appl_ptr(pcm, &svol->plug.appl_ptr, -1, 0);
      *pcmp = pcm;

      return 0;
}

/* in pcm_misc.c */
int snd_pcm_parse_control_id(snd_config_t *conf, snd_ctl_elem_id_t *ctl_id, int *cardp,
                       int *cchannelsp, int *hwctlp);

/*! \page pcm_plugins

\section pcm_plugins_softvol Plugin: Soft Volume

This plugin applies the software volume attenuation.
The format, rate and channels must match for both of source and destination.

When the control is stereo (count=2), the channels are assumed to be either
mono, 2.0, 2.1, 4.0, 4.1, 5.1 or 7.1.

If the control already exists and it's a system control (i.e. no
user-defined control), the plugin simply passes its slave without
any changes.

\code
pcm.name {
        type softvol            # Soft Volume conversion PCM
        slave STR               # Slave name
        # or
        slave {                 # Slave definition
                pcm STR         # Slave PCM name
                # or
                pcm { }         # Slave PCM definition
                [format STR]    # Slave format
        }
        control {
              name STR        # control element id string
            [card STR]      # control card index
            [iface STR]     # interface of the element
            [index INT]     # index of the element
            [device INT]    # device number of the element
            [subdevice INT] # subdevice number of the element
            [count INT]     # control channels 1 or 2 (default: 2)
      }
      [min_dB REAL]           # minimal dB value (default: -48.0)
      [resolution INT]        # resolution (default: 256)
}
\endcode

\subsection pcm_plugins_softvol_funcref Function reference

<UL>
  <LI>snd_pcm_softvol_open()
  <LI>_snd_pcm_softvol_open()
</UL>

*/

/**
 * \brief Creates a new Soft Volume PCM
 * \param pcmp Returns created PCM handle
 * \param name Name of PCM
 * \param root Root configuration node
 * \param conf Configuration node with Soft Volume PCM description
 * \param stream Stream type
 * \param mode Stream mode
 * \retval zero on success otherwise a negative error code
 * \warning Using of this function might be dangerous in the sense
 *          of compatibility reasons. The prototype might be freely
 *          changed in future.
 */
00739 int _snd_pcm_softvol_open(snd_pcm_t **pcmp, const char *name,
                    snd_config_t *root, snd_config_t *conf, 
                    snd_pcm_stream_t stream, int mode)
{
      snd_config_iterator_t i, next;
      int err;
      snd_pcm_t *spcm;
      snd_config_t *slave = NULL, *sconf;
      snd_config_t *control = NULL;
      snd_pcm_format_t sformat = SND_PCM_FORMAT_UNKNOWN;
      snd_ctl_elem_id_t *ctl_id;
      int resolution = PRESET_RESOLUTION;
      double min_dB = PRESET_MIN_DB;
      int card = -1, cchannels = 2;

      snd_config_for_each(i, next, conf) {
            snd_config_t *n = snd_config_iterator_entry(i);
            const char *id;
            if (snd_config_get_id(n, &id) < 0)
                  continue;
            if (snd_pcm_conf_generic_id(id))
                  continue;
            if (strcmp(id, "slave") == 0) {
                  slave = n;
                  continue;
            }
            if (strcmp(id, "control") == 0) {
                  control = n;
                  continue;
            }
            if (strcmp(id, "resolution") == 0) {
                  long v;
                  err = snd_config_get_integer(n, &v);
                  if (err < 0) {
                        SNDERR("Invalid resolution value");
                        return err;
                  }
                  resolution = v;
                  continue;
            }
            if (strcmp(id, "min_dB") == 0) {
                  err = snd_config_get_real(n, &min_dB);
                  if (err < 0) {
                        SNDERR("Invalid min_dB value");
                        return err;
                  }
                  continue;
            }
            SNDERR("Unknown field %s", id);
            return -EINVAL;
      }
      if (!slave) {
            SNDERR("slave is not defined");
            return -EINVAL;
      }
      if (!control) {
            SNDERR("control is not defined");
            return -EINVAL;
      }
      if (min_dB >= 0) {
            SNDERR("min_dB must be a negative value");
            return -EINVAL;
      }
      if (resolution < 0 || resolution > 1024) {
            SNDERR("Invalid resolution value %d", resolution);
            return -EINVAL;
      }
      err = snd_pcm_slave_conf(root, slave, &sconf, 1,
                         SND_PCM_HW_PARAM_FORMAT, 0, &sformat);
      if (err < 0)
            return err;
      if (sformat != SND_PCM_FORMAT_UNKNOWN &&
          sformat != SND_PCM_FORMAT_S16 &&
          sformat != SND_PCM_FORMAT_S32) {
            SNDERR("only S16 or S32 format is supported");
            snd_config_delete(sconf);
            return -EINVAL;
      }
      err = snd_pcm_open_slave(&spcm, root, sconf, stream, mode);
      snd_config_delete(sconf);
      if (err < 0)
            return err;
      snd_ctl_elem_id_alloca(&ctl_id);
      if ((err = snd_pcm_parse_control_id(control, ctl_id, &card, &cchannels, NULL)) < 0) {
            snd_pcm_close(spcm);
            return err;
      }
      err = snd_pcm_softvol_open(pcmp, name, sformat, card, ctl_id, cchannels,
                           min_dB, resolution, spcm, 1);
      if (err < 0)
            snd_pcm_close(spcm);
      return err;
}
#ifndef DOC_HIDDEN
SND_DLSYM_BUILD_VERSION(_snd_pcm_softvol_open, SND_PCM_DLSYM_VERSION);
#endif

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