106 lines
2.1 KiB
C
106 lines
2.1 KiB
C
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/* @(#)z_asinef.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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* Arcsine
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*
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* Input:
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* x - floating point value
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* acosine - indicates acos calculation
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*
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* Output:
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* Arcsine of x.
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*
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* Description:
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* This routine calculates arcsine / arccosine.
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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 p[] = { 0.933935835, -0.504400557 };
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static const float q[] = { 0.560363004e+1, -0.554846723e+1 };
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static const float a[] = { 0.0, 0.785398163 };
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static const float b[] = { 1.570796326, 0.785398163 };
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float
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_DEFUN (asinef, (float, int),
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float x _AND
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int acosine)
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{
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int flag, i;
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int branch = 0;
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float g, res, R, P, Q, y;
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/* Check for special values. */
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i = numtestf (x);
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if (i == NAN || i == INF)
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{
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errno = EDOM;
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if (i == NAN)
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return (x);
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else
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return (z_infinity_f.f);
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}
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y = fabsf (x);
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flag = acosine;
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if (y > 0.5)
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{
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i = 1 - flag;
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/* Check for range error. */
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if (y > 1.0)
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{
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errno = ERANGE;
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return (z_notanum_f.f);
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}
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g = (1 - y) / 2.0;
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y = -2 * sqrt (g);
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branch = 1;
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}
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else
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{
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i = flag;
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if (y < z_rooteps_f)
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res = y;
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else
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g = y * y;
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}
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if (y >= z_rooteps_f || branch == 1)
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{
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/* Calculate the Taylor series. */
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P = (p[1] * g + p[0]) * g;
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Q = (g + q[1]) * g + q[0];
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R = P / Q;
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res = y + y * R;
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}
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/* Calculate asine or acose. */
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if (flag == 0)
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{
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res = (a[i] + res) + a[i];
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if (x < 0.0)
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res = -res;
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}
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else
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{
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if (x < 0.0)
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res = (b[i] + res) + b[i];
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else
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res = (a[i] - res) + a[i];
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}
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return (res);
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}
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