/*** 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 */#undef ZEROTRAP#define BIAS 0x84   /* define the add-in bias for 16 bit samples */#define CLIP 32635unsigned char linear2ulaw(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.**** Craig Reese: IDA/Supercomputing Research Center** 29 September 1989**** 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*/int ulaw2linear(unsigned char ulawbyte) {  static int exp_lut[8] = { 0, 132, 396, 924, 1980, 4092, 8316, 16764 };  int sign, exponent, mantissa, sample;  ulawbyte = ~ulawbyte;  sign = (ulawbyte & 0x80);  exponent = (ulawbyte >> 4) & 0x07;  mantissa = ulawbyte & 0x0F;  sample = exp_lut[exponent] + (mantissa << (exponent + 3));  if(sign != 0) sample = -sample;  return(sample);}