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102 lines
3.5 KiB
C
102 lines
3.5 KiB
C
/*
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* This routine converts from linear to ulaw
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* 29 September 1989
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*
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* Craig Reese: IDA/Supercomputing Research Center
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* Joe Campbell: Department of Defense
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*
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* References:
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* 1) CCITT Recommendation G.711 (very difficult to follow)
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* 2) "A New Digital Technique for Implementation of Any
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* Continuous PCM Companding Law," Villeret, Michel,
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* et al. 1973 IEEE Int. Conf. on Communications, Vol 1,
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* 1973, pg. 11.12-11.17
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* 3) MIL-STD-188-113,"Interoperability and Performance Standards
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* for Analog-to_Digital Conversion Techniques,"
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* 17 February 1987
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*
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* Input: Signed 16 bit linear sample
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* Output: 8 bit ulaw sample
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*/
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#include <glib.h>
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#define ZEROTRAP /* turn on the trap as per the MIL-STD */
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#define BIAS 0x84 /* define the add-in bias for 16 bit samples */
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#define CLIP 32635
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void
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mulaw_encode(gint16* in, guint8* out, gint numsamples)
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{
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static gint16 exp_lut[256] = {0,0,1,1,2,2,2,2,3,3,3,3,3,3,3,3,
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4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,
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5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,
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5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,
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6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,
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6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,
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6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,
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6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,
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7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
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7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
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7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
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7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
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7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
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7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
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7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
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7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7};
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gint16 sign, exponent, mantissa,i;
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gint16 sample;
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guint8 ulawbyte;
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for(i=0;i<numsamples;i++) {
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sample=in[i];
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/** get the sample into sign-magnitude **/
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sign = (sample >> 8) & 0x80; /* set aside the sign */
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if (sign != 0) sample = -sample; /* get magnitude */
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if (sample > CLIP) sample = CLIP; /* clip the magnitude */
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/** convert from 16 bit linear to ulaw **/
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sample = sample + BIAS;
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exponent = exp_lut[(sample>>7) & 0xFF];
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mantissa = (sample >> (exponent+3)) & 0x0F;
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ulawbyte = ~(sign | (exponent << 4) | mantissa);
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#ifdef ZEROTRAP
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if (ulawbyte == 0 ) ulawbyte = 0x02; /* optional CCITT trap */
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#endif
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out[i]=ulawbyte;
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}
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}
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/*
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* This routine converts from ulaw to 16 bit linear
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* 29 September 1989
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*
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* Craig Reese: IDA/Supercomputing Research Center
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*
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* References:
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* 1) CCITT Recommendation G.711 (very difficult to follow)
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* 2) MIL-STD-188-113,"Interoperability and Performance Standards
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* for Analog-to_Digital Conversion Techniques,"
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* 17 February 1987
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*
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* Input: 8 bit ulaw sample
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* Output: signed 16 bit linear sample
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*/
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void
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mulaw_decode(guint8* in,gint16* out,gint numsamples)
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{
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static gint16 exp_lut[8]={0,132,396,924,1980,4092,8316,16764};
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gint16 sign, exponent, mantissa;
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guint8 ulawbyte;
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gint16 linear,i;
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for(i=0;i<numsamples;i++) {
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ulawbyte=in[i];
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ulawbyte = ~ulawbyte;
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sign = (ulawbyte & 0x80);
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exponent = (ulawbyte >> 4) & 0x07;
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mantissa = ulawbyte & 0x0F;
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linear = exp_lut[exponent] + (mantissa << (exponent+3));
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if (sign != 0) linear = -linear;
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out[i]=linear;
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}
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}
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