59 lines
1 KiB
C
59 lines
1 KiB
C
/* $Header$ */
|
|
|
|
#include <pc_err.h>
|
|
|
|
extern double _fef();
|
|
extern _trp();
|
|
|
|
/*
|
|
log returns the natural logarithm of its floating
|
|
point argument.
|
|
|
|
The coefficients are #2705 from Hart & Cheney. (19.38D)
|
|
|
|
It calls _fef.
|
|
*/
|
|
|
|
#define HUGE 1.701411733192644270e38
|
|
|
|
static double log2 = 0.693147180559945309e0;
|
|
static double sqrto2 = 0.707106781186547524e0;
|
|
static double p0 = -.240139179559210510e2;
|
|
static double p1 = 0.309572928215376501e2;
|
|
static double p2 = -.963769093368686593e1;
|
|
static double p3 = 0.421087371217979714e0;
|
|
static double q0 = -.120069589779605255e2;
|
|
static double q1 = 0.194809660700889731e2;
|
|
static double q2 = -.891110902798312337e1;
|
|
|
|
double
|
|
_log(arg)
|
|
double arg;
|
|
{
|
|
double x,z, zsq, temp;
|
|
int exp;
|
|
|
|
if(arg <= 0) {
|
|
_trp(ELOG);
|
|
return(-HUGE);
|
|
}
|
|
x = _fef(arg,&exp);
|
|
/*
|
|
while(x < 0.5) {
|
|
x =* 2;
|
|
exp--;
|
|
}
|
|
*/
|
|
if(x<sqrto2) {
|
|
x *= 2;
|
|
exp--;
|
|
}
|
|
|
|
z = (x-1)/(x+1);
|
|
zsq = z*z;
|
|
|
|
temp = ((p3*zsq + p2)*zsq + p1)*zsq + p0;
|
|
temp = temp/(((zsq + q2)*zsq + q1)*zsq + q0);
|
|
temp = temp*z + exp*log2;
|
|
return(temp);
|
|
}
|