mirror of
https://gitlab.freedesktop.org/gstreamer/gstreamer.git
synced 2024-12-25 01:30:38 +00:00
102 lines
3.5 KiB
C
102 lines
3.5 KiB
C
/*
|
|
* 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
|
|
*/
|
|
|
|
#include <glib.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
|
|
|
|
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 */
|
|
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
|
|
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;
|
|
}
|
|
}
|