#ifndef lint
static char sccsid[] = "@(#)libst.c	1.2 (UKC) 12/3/89";
#endif
/* libst.c - portable sound tools library
*/

/*
** This routine converts from linear to ulaw.
**
** Craig Reese: IDA/Supercomputing Research Center
** Joe Campbell: Department of Defense
** 29 September 1989
**
** 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
*/

#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

unsigned char
st_linear_to_ulaw( sample )
int sample;
    {
    static int 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};
    int sign, exponent, mantissa;
    unsigned char ulawbyte;

    /* 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

    return ulawbyte;
    }

/*
** This routine converts from ulaw to 16 bit linear, but faster.
**
** Jef Poskanzer
** 23 October 1989
**
** Input: 8 bit ulaw sample
** Output: signed 16 bit linear sample
*/

int
st_ulaw_to_linear( ulawbyte )
unsigned char ulawbyte;
{
    static int ulaw_table[] = {
	-32124, -31100, -30076, -29052, -28028, -27004, -25980, -24956, 
	-23932, -22908, -21884, -20860, -19836, -18812, -17788, -16764, 
	-15996, -15484, -14972, -14460, -13948, -13436, -12924, -12412, 
	-11900, -11388, -10876, -10364,  -9852,  -9340,  -8828,  -8316, 
	 -7932,  -7676,  -7420,  -7164,  -6908,  -6652,  -6396,  -6140, 
	 -5884,  -5628,  -5372,  -5116,  -4860,  -4604,  -4348,  -4092, 
	 -3900,  -3772,  -3644,  -3516,  -3388,  -3260,  -3132,  -3004, 
	 -2876,  -2748,  -2620,  -2492,  -2364,  -2236,  -2108,  -1980, 
	 -1884,  -1820,  -1756,  -1692,  -1628,  -1564,  -1500,  -1436, 
	 -1372,  -1308,  -1244,  -1180,  -1116,  -1052,   -988,   -924, 
	  -876,   -844,   -812,   -780,   -748,   -716,   -684,   -652, 
	  -620,   -588,   -556,   -524,   -492,   -460,   -428,   -396, 
	  -372,   -356,   -340,   -324,   -308,   -292,   -276,   -260, 
	  -244,   -228,   -212,   -196,   -180,   -164,   -148,   -132, 
	  -120,   -112,   -104,    -96,    -88,    -80,    -72,    -64, 
	   -56,    -48,    -40,    -32,    -24,    -16,     -8,      0, 
	 32124,  31100,  30076,  29052,  28028,  27004,  25980,  24956, 
	 23932,  22908,  21884,  20860,  19836,  18812,  17788,  16764, 
	 15996,  15484,  14972,  14460,  13948,  13436,  12924,  12412, 
	 11900,  11388,  10876,  10364,   9852,   9340,   8828,   8316, 
	  7932,   7676,   7420,   7164,   6908,   6652,   6396,   6140, 
	  5884,   5628,   5372,   5116,   4860,   4604,   4348,   4092, 
	  3900,   3772,   3644,   3516,   3388,   3260,   3132,   3004, 
	  2876,   2748,   2620,   2492,   2364,   2236,   2108,   1980, 
	  1884,   1820,   1756,   1692,   1628,   1564,   1500,   1436, 
	  1372,   1308,   1244,   1180,   1116,   1052,    988,    924, 
	   876,    844,    812,    780,    748,    716,    684,    652, 
	   620,    588,    556,    524,    492,    460,    428,    396, 
	   372,    356,    340,    324,    308,    292,    276,    260, 
	   244,    228,    212,    196,    180,    164,    148,    132, 
	   120,    112,    104,     96,     88,     80,     72,     64, 
	    56,     48,     40,     32,     24,     16,      8,      0 };

    return ulaw_table[ulawbyte];
    }