gstreamer/gst/law/mulaw-conversion.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;
    }
}