/*  * gus_vol.c - Compute volume for GUS. *  * Greg Lee 1993. */#include "sound_config.h"#ifndef EXCLUDE_GUS#define GUS_VOLUME	gus_wave_volumeextern int      gus_wave_volume;/*  * Calculate gus volume from note velocity, main volume, expression, and * intrinsic patch volume given in patch library.  Expression is multiplied * in, so it emphasizes differences in note velocity, while main volume is * added in -- I don't know whether this is right, but it seems reasonable to * me.  (In the previous stage, main volume controller messages were changed * to expression controller messages, if they were found to be used for * dynamic volume adjustments, so here, main volume can be assumed to be * constant throughout a song.) *  * Intrinsic patch volume is added in, but if over 64 is also multiplied in, so * we can give a big boost to very weak voices like nylon guitar and the * basses.  The normal value is 64.  Strings are assigned lower values. */unsigned shortgus_adagio_vol (int vel, int mainv, int xpn, int voicev){  int             i, m, n, x;  /*    * A voice volume of 64 is considered neutral, so adjust the main volume if   * something other than this neutral value was assigned in the patch   * library.   */  x = 256 + 6 * (voicev - 64);  /*    * Boost expression by voice volume above neutral.    */  if (voicev > 65)    xpn += voicev - 64;  xpn += (voicev - 64) / 2;  /*    * Combine multiplicative and level components.    */  x = vel * xpn * 6 + (voicev / 4) * x;#ifdef GUS_VOLUME  /*    * Further adjustment by installation-specific master volume control   * (default 60).   */  x = (x * GUS_VOLUME * GUS_VOLUME) / 10000;#endif#ifdef GUS_USE_CHN_MAIN_VOLUME  /*   * Experimental support for the channel main volume   */   mainv = (mainv / 2) + 64;  /* Scale to 64 to 127 */   x = (x * mainv * mainv) / 16384;#endif  if (x < 2)    return (0);  else if (x >= 65535)    return ((15 << 8) | 255);  /*    * Convert to gus's logarithmic form with 4 bit exponent i and 8 bit   * mantissa m.   */  n = x;  i = 7;  if (n < 128)    {      while (i > 0 && n < (1 << i))	i--;    }  else    while (n > 255)      {	n >>= 1;	i++;      }  /*    * Mantissa is part of linear volume not expressed in exponent.  (This is   * not quite like real logs -- I wonder if it's right.)   */  m = x - (1 << i);  /*    * Adjust mantissa to 8 bits.    */  if (m > 0)    {      if (i > 8)	m >>= i - 8;      else if (i < 8)	m <<= 8 - i;    }  return ((i << 8) + m);}#endif