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/* @(#)z_logarithmf.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.
******************************************************************/
/******************************************************************
* Logarithm
*
* Input:
* x - floating point value
* ten - indicates base ten numbers
*
* Output:
* logarithm of x
*
* Description:
* This routine calculates logarithms.
*
*****************************************************************/
#include "fdlibm.h"
#include "zmath.h"
static const float a[] = { -0.5527074855 };
static const float b[] = { -0.6632718214e+1 };
static const float C1 = 0.693145752;
static const float C2 = 1.428606820e-06;
static const float C3 = 0.4342944819;
float
_DEFUN (logarithmf, (float, int),
float x _AND
int ten)
{
int N;
float f, w, z;
/* Check for domain error here. */
if (x <= 0.0)
{
errno = ERANGE;
return (z_notanum_f.f);
}
/* Get the exponent and mantissa where x = f * 2^N. */
f = frexpf (x, &N);
z = f - 0.5;
if (f > __SQRT_HALF)
z = (z - 0.5) / (f * 0.5 + 0.5);
else
{
N--;
z /= (z * 0.5 + 0.5);
}
w = z * z;
/* Use Newton's method with 4 terms. */
z += z * w * (a[0]) / ((w + 1.0) * w + b[0]);
if (N != 0)
z = (N * C2 + z) + N * C1;
if (ten)
z *= C3;
return (z);
}
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