141 lines
2.9 KiB
C
141 lines
2.9 KiB
C
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/* @(#)z_atangentf.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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* Arctangent
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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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* arctangent of x
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*
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* Description:
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* This routine calculates arctangents.
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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 ROOT3 = 1.732050807;
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static const float a[] = { 0.0, 0.523598775, 1.570796326,
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1.047197551 };
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static const float q[] = { 0.1412500740e+1 };
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static const float p[] = { -0.4708325141, -0.5090958253e-1 };
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float
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_DEFUN (atangentf, (float, float, float, int),
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float x _AND
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float v _AND
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float u _AND
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int arctan2)
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{
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float f, g, R, P, Q, A, res;
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int N;
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int branch = 0;
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int expv, expu;
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/* Preparation for calculating arctan2. */
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if (arctan2)
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{
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if (u == 0.0)
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if (v == 0.0)
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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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else
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{
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branch = 1;
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res = __PI_OVER_TWO;
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}
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if (!branch)
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{
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int e;
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/* Get the exponent values of the inputs. */
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g = frexpf (v, &expv);
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g = frexpf (u, &expu);
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/* See if a divide will overflow. */
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e = expv - expu;
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if (e > FLT_MAX_EXP)
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{
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branch = 1;
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res = __PI_OVER_TWO;
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}
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/* Also check for underflow. */
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else if (e < FLT_MIN_EXP)
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{
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branch = 2;
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res = 0.0;
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}
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}
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}
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if (!branch)
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{
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if (arctan2)
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f = fabsf (v / u);
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else
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f = fabsf (x);
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if (f > 1.0)
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{
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f = 1.0 / f;
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N = 2;
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}
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else
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N = 0;
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if (f > (2.0 - ROOT3))
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{
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A = ROOT3 - 1.0;
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f = (((A * f - 0.5) - 0.5) + f) / (ROOT3 + f);
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N++;
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}
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/* Check for values that are too small. */
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if (-z_rooteps_f < f && f < z_rooteps_f)
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res = f;
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/* Calculate the Taylor series. */
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else
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{
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g = f * f;
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P = (p[1] * g + p[0]) * g;
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Q = g + q[0];
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R = P / Q;
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res = f + f * R;
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}
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if (N > 1)
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res = -res;
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res += a[N];
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}
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if (arctan2)
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{
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if (u < 0.0 || branch == 2)
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res = __PI - res;
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if (v < 0.0 || branch == 1)
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res = -res;
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}
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else if (x < 0.0)
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{
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res = -res;
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}
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return (res);
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}
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