63 lines
1.4 KiB
C
63 lines
1.4 KiB
C
/* _Exp function */
|
|
#include "wctype.h"
|
|
#include "xmath.h"
|
|
_STD_BEGIN
|
|
|
|
/* coefficients */
|
|
static const double p[] = { /* courtesy Dr. Tim Prince */
|
|
1.0,
|
|
420.30235984910635,
|
|
15132.70094680474802};
|
|
static const double q[] = { /* courtesy Dr. Tim Prince */
|
|
30.01511290683317,
|
|
3362.72154416553028,
|
|
30265.40189360949691};
|
|
static const double c1 = 22713.0 / 32768.0;
|
|
static const double c2 = 1.428606820309417232e-6L;
|
|
static const double hugexp = HUGE_EXP;
|
|
static const double invln2 = 1.4426950408889634074L;
|
|
|
|
_CRTIMP2 short __cdecl _Exp(double *px, double y, short eoff)
|
|
{ /* compute y*e^(*px), (*px) finite, |y| not huge */
|
|
if (*px < -hugexp || y == 0)
|
|
{ /* certain underflow */
|
|
*px = 0;
|
|
return (0);
|
|
}
|
|
else if (hugexp < *px)
|
|
{ /* certain overflow */
|
|
*px = _Inf._D;
|
|
return (INF);
|
|
}
|
|
else
|
|
{ /* xexp won't overflow */
|
|
double g = *px * invln2;
|
|
short xexp = g + (g < 0 ? - 0.5 : + 0.5);
|
|
|
|
g = xexp;
|
|
g = (*px - g * c1) - g * c2;
|
|
if (-_Eps._D < g && g < _Eps._D)
|
|
*px = y;
|
|
else
|
|
{ /* g*g worth computing */
|
|
const double z = g * g;
|
|
const double w = (q[0] * z + q[1]) * z + q[2];
|
|
|
|
g *= (z + p[1]) * z + p[2];
|
|
*px = (w + g) / (w - g) * 2 * y;
|
|
--xexp;
|
|
}
|
|
return (_Dscale(px, (long)xexp + eoff));
|
|
}
|
|
}
|
|
_STD_END
|
|
|
|
/*
|
|
* Copyright (c) 1994 by P.J. Plauger. ALL RIGHTS RESERVED.
|
|
* Consult your license regarding permissions and restrictions.
|
|
*/
|
|
|
|
/*
|
|
941029 pjp: added _STD machinery
|
|
*/
|