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118 lines
3.6 KiB
C
118 lines
3.6 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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#ifdef HAVE_CONFIG_H
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#include "config.h"
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#endif
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#include <glib.h>
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#include "mulaw-conversion.h"
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#undef 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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};
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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) {
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sample = -sample; /* get magnitude */
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}
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/* sample can be zero because we can overflow in the inversion,
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* checking against the unsigned version solves this */
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if (((guint16) sample) > CLIP)
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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)
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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)
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linear = -linear;
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out[i] = linear;
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}
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}
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