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78 lines
1.6 KiB
C
78 lines
1.6 KiB
C
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/* @(#)z_tanhf.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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* Hyperbolic 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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* hyperbolic tangent of x
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*
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* Description:
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* This routine calculates hyperbolic tangent.
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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 LN3_OVER2 = 0.5493061443;
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static const float p[] = { -0.2059432032,
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-0.0009577527 };
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static const float q[] = { 0.6178299136,
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0.25 };
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float
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_DEFUN (tanhf, (float),
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float x)
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{
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float f, res, g, P, Q, R;
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f = fabsf (x);
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/* Check if the input is too big. */
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if (f > BIGX)
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res = 1.0;
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else if (f > LN3_OVER2)
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res = 1.0 - 2.0 / (exp (2 * f) + 1.0);
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/* Check if the input is too small. */
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else if (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];
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Q = (g + q[1]) * g + q[0];
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R = g * (P / Q);
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res = f + f * R;
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}
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if (x < 0.0)
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res = -res;
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return (res);
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}
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#ifdef _DOUBLE_IS_32BITS
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double tanh (double x)
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{
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return (double) tanhf ((float) x);
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}
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#endif _DOUBLE_IS_32BITS
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