104 lines
2.0 KiB
C
104 lines
2.0 KiB
C
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/* @(#)z_tanf.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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* Tangent
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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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* tangent of x
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*
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* Description:
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* This routine calculates the tangent of x.
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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 TWO_OVER_PI = 0.6366197723;
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static const float p[] = { -0.958017723e-1 };
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static const float q[] = { -0.429135777,
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0.971685835e-2 };
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float
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tanf (float x)
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{
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float y, f, g, XN, xnum, xden, res;
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int N;
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/* Check for special values. */
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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 = EDOM;
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return (z_notanum_f.f);
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}
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y = fabsf (x);
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/* Check for values that are out of our range. */
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if (y > 105414357.0)
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{
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errno = ERANGE;
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return (y);
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}
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if (x < 0.0)
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N = (int) (x * TWO_OVER_PI - 0.5);
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else
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N = (int) (x * TWO_OVER_PI + 0.5);
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XN = (float) N;
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f = x - N * __PI_OVER_TWO;
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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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{
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xnum = f;
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xden = 1.0;
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}
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/* Calculate the polynomial. */
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else
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{
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g = f * f;
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xnum = f * (p[0] * g) + f;
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xden = (q[1] * g + q[0]) * g + 1.0;
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}
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/* Check for odd or even values. */
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if (N & 1)
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{
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xnum = -xnum;
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res = xden / xnum;
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}
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else
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{
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res = xnum / xden;
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}
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return (res);
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}
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#ifdef _DOUBLE_IS_32BITS
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double tan (double x)
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{
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return (double) tanf ((float) x);
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}
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#endif /* _DOUBLE_IS_32BITS */
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