Trailing-Edge
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PDP-10 Archives
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SRI_NIC_PERM_FS_1_19910112
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kccdist/lib/math/pow.c
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/*
* POW.C - computes the power function
*
* This code conforms with the description of the pow function as
* described in Harbison & Steele's "C: A Reference Manual", section
* 11.3.19
*/
#include "math.h"
#include "errno.h"
#define power(x, y) (exp((y) * log(x)))
double pow(x, y)
double x, y;
{
double i;
if (x > 0) {
if (y == 0)
return 1.0;
else if (y > 0)
return power(x, y);
else /* (y < 0) */
return 1.0 / power(x, -y);
}
else if (x == 0) {
if (y > 0)
return 0.0;
else {
errno = EDOM;
return MAX_NEG_DBLF;
}
}
else { /* (x < 0) */
if (modf(y, &i) == 0.0) {
if (y == 0)
return 1.0;
else if (y > 0)
return -power(-x, y);
else
return -1.0 / power(-x, -y);
}
else {
errno = EDOM;
return MAX_NEG_DBLF;
}
}
}