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/* @(#)z_expf.c 1.0 98/08/13 */
/******************************************************************
* The following routines are coded directly from the algorithms
* and coefficients given in "Software Manual for the Elementary
* Functions" by William J. Cody, Jr. and William Waite, Prentice
* Hall, 1980.
******************************************************************/
/******************************************************************
* Exponential Function
*
* Input:
* x - floating point value
*
* Output:
* e raised to x.
*
* Description:
* This routine returns e raised to the xth power.
*
*****************************************************************/
#include <float.h>
#include "fdlibm.h"
#include "zmath.h"
static const float INV_LN2 = 1.442695040;
static const float LN2 = 0.693147180;
static const float p[] = { 0.249999999950, 0.00416028863 };
static const float q[] = { 0.5, 0.04998717878 };
float
_DEFUN (expf, (float),
float x)
{
int N;
float g, z, R, P, Q;
switch (numtestf (x))
{
case NAN:
errno = EDOM;
return (x);
case INF:
errno = ERANGE;
if (isposf (x))
return (z_infinity_f.f);
else
return (0.0);
case 0:
return (1.0);
}
/* Check for out of bounds. */
if (x > BIGX || x < SMALLX)
{
errno = ERANGE;
return (x);
}
/* Check for a value too small to calculate. */
if (-z_rooteps_f < x && x < z_rooteps_f)
{
return (1.0);
}
/* Calculate the exponent. */
if (x < 0.0)
N = (int) (x * INV_LN2 - 0.5);
else
N = (int) (x * INV_LN2 + 0.5);
/* Construct the mantissa. */
g = x - N * LN2;
z = g * g;
P = g * (p[1] * z + p[0]);
Q = q[1] * z + q[0];
R = 0.5 + P / (Q - P);
/* Return the floating point value. */
N++;
return (ldexpf (R, N));
}
#ifdef _DOUBLE_IS_32BITS
double exp (double x)
{
return (double) expf ((float) x);
}
#endif /* _DOUBLE_IS_32BITS */
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