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/*
* BRLTTY - A background process providing access to the console screen (when in
* text mode) for a blind person using a refreshable braille display.
*
* Copyright (C) 1995-2014 by The BRLTTY Developers.
*
* BRLTTY comes with ABSOLUTELY NO WARRANTY.
*
* This is free software, placed under the terms of the
* GNU General Public License, as published by the Free Software
* Foundation; either version 2 of the License, or (at your option) any
* later version. Please see the file LICENSE-GPL for details.
*
* Web Page: http://mielke.cc/brltty/
*
* This software is maintained by Dave Mielke <dave@mielke.cc>.
*/
#include "prologue.h"
#include "pcm.h"
typedef struct {
unsigned char size;
} PcmSampleEntry;
static const PcmSampleEntry pcmSampleTable[] = {
[PCM_FMT_U8] = {
.size = 1
},
[PCM_FMT_S8] = {
.size = 1
},
[PCM_FMT_U16B] = {
.size = 2
},
[PCM_FMT_S16B] = {
.size = 2
},
[PCM_FMT_U16L] = {
.size = 2
},
[PCM_FMT_S16L] = {
.size = 2
},
[PCM_FMT_U16N] = {
.size = 2
},
[PCM_FMT_S16N] = {
.size = 2
},
[PCM_FMT_ULAW] = {
.size = 1
},
[PCM_FMT_ALAW] = {
.size = 1
}
};
size_t
getPcmSampleLength (PcmAmplitudeFormat format) {
return (format < ARRAY_COUNT(pcmSampleTable))? pcmSampleTable[format].size: 0;
}
size_t
makePcmSample (
PcmAmplitudeFormat format, int16_t amplitude,
void *buffer, size_t size
) {
size_t length = getPcmSampleLength(format);
if (size >= length) {
typedef union {
unsigned char bytes[4];
int16_t s16N;
} Sample;
Sample *sample = buffer;
const int U2S = 0X8000;
switch (format) {
case PCM_FMT_U8:
amplitude += U2S;
case PCM_FMT_S8:
sample->bytes[0] = amplitude >> 8;
break;
case PCM_FMT_U16B:
amplitude += U2S;
case PCM_FMT_S16B:
sample->bytes[0] = amplitude >> 8;
sample->bytes[1] = amplitude;
break;
case PCM_FMT_U16L:
amplitude += U2S;
case PCM_FMT_S16L:
sample->bytes[0] = amplitude;
sample->bytes[1] = amplitude >> 8;
break;
case PCM_FMT_U16N:
amplitude += U2S;
case PCM_FMT_S16N:
sample->s16N = amplitude;
break;
case PCM_FMT_ULAW: {
int negative = amplitude < 0;
int exponent = 0X7;
unsigned char value;
const unsigned int bias = 0X84;
const unsigned int clip = 0X7FFF - bias;
if (negative) amplitude = -amplitude;
if (amplitude > clip) amplitude = clip;
amplitude += bias;
while ((exponent > 0) && !(amplitude & 0X4000)) {
amplitude <<= 1;
--exponent;
}
value = (exponent << 4) | ((amplitude >> 10) & 0X0F);
if (negative) value |= 0X80;
sample->bytes[0] = ~value;
break;
}
case PCM_FMT_ALAW: {
int negative = amplitude < 0;
int exponent = 0X7;
unsigned char value;
if (negative) amplitude = -amplitude;
while ((exponent > 0) && !(amplitude & 0X4000)) {
amplitude <<= 1;
--exponent;
}
if (!exponent) amplitude >>= 1;
value = (exponent << 4) | ((amplitude >> 10) & 0X0F);
if (negative) value |= 0X80;
sample->bytes[0] = value ^ 0X55;
break;
}
default:
length = 0;
break;
}
}
return length;
}
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