src/pcm_volume.h

   1 /*
   2  * Copyright (C) 2003-2009 The Music Player Daemon Project
   3  * http://www.musicpd.org
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License along
  16  * with this program; if not, write to the Free Software Foundation, Inc.,
  17  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  18  */
  19
  20 #ifndef PCM_VOLUME_H
  21 #define PCM_VOLUME_H
  22
  23 #include "pcm_prng.h"
  24
  25 #include <stdint.h>
  26 #include <stdbool.h>
  27
  28 enum {
  29         /** this value means "100% volume" */
  30         PCM_VOLUME_1 = 1024,
  31 };
  32
  33 struct audio_format;
  34
  35 /**
  36  * Converts a float value (0.0 = silence, 1.0 = 100% volume) to an
  37  * integer volume value (1000 = 100%).
  38  */
  39 static inline int
  40 pcm_float_to_volume(float volume)
  41 {
  42         return volume * PCM_VOLUME_1 + 0.5;
  43 }
  44
  45 /**
  46  * Returns the next volume dithering number, between -511 and +511.
  47  * This number is taken from a global PRNG, see pcm_prng().
  48  */
  49 static inline int
  50 pcm_volume_dither(void)
  51 {
  52         static unsigned long state;
  53         uint32_t r;
  54
  55         r = state = pcm_prng(state);
  56
  57         return (r & 511) - ((r >> 9) & 511);
  58 }
  59
  60 /**
  61  * Adjust the volume of the specified PCM buffer.
  62  *
  63  * @param buffer the PCM buffer
  64  * @param length the length of the PCM buffer
  65  * @param format the audio format of the PCM buffer
  66  * @param volume the volume between 0 and #PCM_VOLUME_1
  67  * @return true on success, false if the audio format is not supported
  68  */
  69 bool
  70 pcm_volume(void *buffer, int length,
  71            const struct audio_format *format,
  72            int volume);
  73
  74 #endif