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70317d8506
* libm/mathfp/s_logarithm.c: Fix error introduced by previous
fix when handling negative input values. Make function
consistent with math directory and glibc version such that
inf and nan values return inf and nan respectively with no
errno setting.
* libm/mathfp/sf_logarithm.c: Ditto.
* libm/math/w_log.c: Set errno to ERANGE when input is 0.0.
* libm/math/wf_log.c: Ditto.
* libm/math/w_log10.c: Ditto.
* libm/math/wf_log10.c: Ditto.
85 lines
1.8 KiB
C
85 lines
1.8 KiB
C
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/* @(#)z_logarithmf.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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* Logarithm
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*
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* Input:
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* x - floating point value
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* ten - indicates base ten numbers
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*
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* Output:
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* logarithm of x
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*
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* Description:
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* This routine calculates logarithms.
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*
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*****************************************************************/
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#include "fdlibm.h"
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#include "zmath.h"
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static const float a[] = { -0.5527074855 };
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static const float b[] = { -0.6632718214e+1 };
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static const float C1 = 0.693145752;
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static const float C2 = 1.428606820e-06;
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static const float C3 = 0.4342944819;
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float
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_DEFUN (logarithmf, (float, int),
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float x _AND
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int ten)
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{
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int N;
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float f, w, z;
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/* Check for domain/range errors here. */
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if (x == 0.0)
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{
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errno = ERANGE;
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return (-z_infinity_f.f);
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}
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else if (x < 0.0)
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{
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errno = EDOM;
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return (z_notanum_f.f);
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}
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else if (!isfinitef(x))
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{
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if (isnanf(x))
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return (z_notanum_f.f);
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else
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return (z_infinity_f.f);
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}
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/* Get the exponent and mantissa where x = f * 2^N. */
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f = frexpf (x, &N);
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z = f - 0.5;
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if (f > __SQRT_HALF)
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z = (z - 0.5) / (f * 0.5 + 0.5);
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else
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{
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N--;
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z /= (z * 0.5 + 0.5);
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}
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w = z * z;
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/* Use Newton's method with 4 terms. */
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z += z * w * (a[0]) / ((w + 1.0) * w + b[0]);
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if (N != 0)
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z = (N * C2 + z) + N * C1;
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if (ten)
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z *= C3;
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return (z);
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}
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