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