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/*
* This routine converts from linear to ulaw
* 29 September 1989
*
* Craig Reese: IDA/Supercomputing Research Center
* Joe Campbell: Department of Defense
*
* References:
* 1) CCITT Recommendation G.711 (very difficult to follow)
* 2) "A New Digital Technique for Implementation of Any
* Continuous PCM Companding Law," Villeret, Michel,
* et al. 1973 IEEE Int. Conf. on Communications, Vol 1,
* 1973, pg. 11.12-11.17
* 3) MIL-STD-188-113,"Interoperability and Performance Standards
* for Analog-to_Digital Conversion Techniques,"
* 17 February 1987
*
* Input: Signed 16 bit linear sample
* Output: 8 bit ulaw sample
*/
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
#include <glib.h>
#undef 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
void
mulaw_encode (gint16 * in, guint8 * out, gint numsamples)
{
static gint16 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
};
gint16 sign, exponent, mantissa, i;
gint16 sample;
guint8 ulawbyte;
for (i = 0; i < numsamples; i++) {
sample = in[i];
/** get the sample into sign-magnitude **/
sign = (sample >> 8) & 0x80; /* set aside the sign */
if (sign != 0) {
sample = -sample; /* get magnitude */
}
/* sample can be zero because we can overflow in the inversion,
* checking against the unsigned version solves this */
if (((guint16) 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
out[i] = ulawbyte;
}
}
/*
* This routine converts from ulaw to 16 bit linear
* 29 September 1989
*
* Craig Reese: IDA/Supercomputing Research Center
*
* References:
* 1) CCITT Recommendation G.711 (very difficult to follow)
* 2) MIL-STD-188-113,"Interoperability and Performance Standards
* for Analog-to_Digital Conversion Techniques,"
* 17 February 1987
*
* Input: 8 bit ulaw sample
* Output: signed 16 bit linear sample
*/
void
mulaw_decode (guint8 * in, gint16 * out, gint numsamples)
{
static gint16 exp_lut[8] = { 0, 132, 396, 924, 1980, 4092, 8316, 16764 };
gint16 sign, exponent, mantissa;
guint8 ulawbyte;
gint16 linear, i;
for (i = 0; i < numsamples; i++) {
ulawbyte = in[i];
ulawbyte = ~ulawbyte;
sign = (ulawbyte & 0x80);
exponent = (ulawbyte >> 4) & 0x07;
mantissa = ulawbyte & 0x0F;
linear = exp_lut[exponent] + (mantissa << (exponent + 3));
if (sign != 0)
linear = -linear;
out[i] = linear;
}
}
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