89 lines
2.6 KiB
C
Executable File
89 lines
2.6 KiB
C
Executable File
/*
|
|
* Asterisk -- A telephony toolkit for Linux.
|
|
*
|
|
* u-Law to Signed linear conversion
|
|
*
|
|
* Copyright (C) 1999, Mark Spencer
|
|
*
|
|
* Mark Spencer <markster@linux-support.net>
|
|
*
|
|
* This program is free software, distributed under the terms of
|
|
* the GNU General Public License
|
|
*/
|
|
|
|
#include <asterisk/ulaw.h>
|
|
|
|
#define ZEROTRAP /* turn on the trap as per the MIL-STD */
|
|
#define BIAS 0x84 /* define the add-in bias for 16 bit samples */
|
|
#define CLIP 32635
|
|
|
|
unsigned char ast_lin2mu[65536];
|
|
short ast_mulaw[256];
|
|
|
|
static unsigned char
|
|
linear2ulaw(short sample)
|
|
{
|
|
static int exp_lut[256] = {0,0,1,1,2,2,2,2,3,3,3,3,3,3,3,3,
|
|
4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,
|
|
5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,
|
|
5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,
|
|
6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,
|
|
6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,
|
|
6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,
|
|
6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,
|
|
7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
|
|
7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
|
|
7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
|
|
7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
|
|
7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
|
|
7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
|
|
7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
|
|
7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7};
|
|
int sign, exponent, mantissa;
|
|
unsigned char ulawbyte;
|
|
|
|
/* Get the sample into sign-magnitude. */
|
|
sign = (sample >> 8) & 0x80; /* set aside the sign */
|
|
if (sign != 0) sample = -sample; /* get magnitude */
|
|
if (sample > CLIP) sample = CLIP; /* clip the magnitude */
|
|
|
|
/* Convert from 16 bit linear to ulaw. */
|
|
sample = sample + BIAS;
|
|
exponent = exp_lut[(sample >> 7) & 0xFF];
|
|
mantissa = (sample >> (exponent + 3)) & 0x0F;
|
|
ulawbyte = ~(sign | (exponent << 4) | mantissa);
|
|
#ifdef ZEROTRAP
|
|
if (ulawbyte == 0) ulawbyte = 0x02; /* optional CCITT trap */
|
|
#endif
|
|
|
|
return(ulawbyte);
|
|
}
|
|
|
|
void ast_ulaw_init(void)
|
|
{
|
|
int i;
|
|
/*
|
|
* Set up mu-law conversion table
|
|
*/
|
|
for(i = 0;i < 256;i++)
|
|
{
|
|
short mu,e,f,y;
|
|
static short etab[]={0,132,396,924,1980,4092,8316,16764};
|
|
|
|
mu = 255-i;
|
|
e = (mu & 0x70)/16;
|
|
f = mu & 0x0f;
|
|
y = f * (1 << (e + 3));
|
|
y += etab[e];
|
|
if (mu & 0x80) y = -y;
|
|
ast_mulaw[i] = y;
|
|
}
|
|
/* set up the reverse (mu-law) conversion table */
|
|
for(i = 0; i < 65536; i++)
|
|
{
|
|
ast_lin2mu[i] = linear2ulaw(i - 32768);
|
|
}
|
|
|
|
}
|
|
|