4.3BSD/usr/contrib/icon/rt/exp.c

Compare this file to the similar file:
Show the results in this format:
/*
 * exp - calculate the exponential function of arg.
 *
 *   The coefficients are #1069 from Hart and Cheney. (22.35D)
 */

#include <errno.h>
#include <math.h>

int   errno;
static double   p0   = .2080384346694663001443843411e7;
static double   p1   = .3028697169744036299076048876e5;
static double   p2   = .6061485330061080841615584556e2;
static double   q0   = .6002720360238832528230907598e7;
static double   q1   = .3277251518082914423057964422e6;
static double   q2   = .1749287689093076403844945335e4;
static double   log2e   = 1.4426950408889634073599247;
static double   sqrt2   = 1.4142135623730950488016887;
static double   maxf   = 10000;

double
exp(arg)
double arg;
   {
   double fract;
   double temp1, temp2, xsq;
   int ent;

   if(arg == 0.)
      return(1.);
   if(arg < -maxf)
      return(0.);
   if(arg > maxf) {
      errno = ERANGE;
      return(HUGE);
   }
   arg *= log2e;
   ent = floor(arg);
   fract = (arg-ent) - 0.5;
   xsq = fract*fract;
   temp1 = ((p2*xsq+p1)*xsq+p0)*fract;
   temp2 = ((1.0*xsq+q2)*xsq+q1)*xsq + q0;
   return(ldexp(sqrt2*(temp2+temp1)/(temp2-temp1), ent));
   }