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[/] [openrisc/] [trunk/] [gnu-stable/] [newlib-1.18.0/] [newlib/] [libm/] [mathfp/] [s_tanh.c] - Rev 207
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/* @(#)z_tanh.c 1.0 98/08/13 */ /***************************************************************** * The following routines are coded directly from the algorithms * and coefficients given in "Software Manual for the Elementary * Functions" by William J. Cody, Jr. and William Waite, Prentice * Hall, 1980. *****************************************************************/ /* FUNCTION <<tanh>>, <<tanhf>>---hyperbolic tangent INDEX tanh INDEX tanhf ANSI_SYNOPSIS #include <math.h> double tanh(double <[x]>); float tanhf(float <[x]>); TRAD_SYNOPSIS #include <math.h> double tanh(<[x]>) double <[x]>; float tanhf(<[x]>) float <[x]>; DESCRIPTION <<tanh>> computes the hyperbolic tangent of the argument <[x]>. Angles are specified in radians. <<tanh(<[x]>)>> is defined as . sinh(<[x]>)/cosh(<[x]>) <<tanhf>> is identical, save that it takes and returns <<float>> values. RETURNS The hyperbolic tangent of <[x]> is returned. PORTABILITY <<tanh>> is ANSI C. <<tanhf>> is an extension. */ /****************************************************************** * Hyperbolic Tangent * * Input: * x - floating point value * * Output: * hyperbolic tangent of x * * Description: * This routine calculates hyperbolic tangent. * *****************************************************************/ #include <float.h> #include "fdlibm.h" #include "zmath.h" #ifndef _DOUBLE_IS_32BITS static const double LN3_OVER2 = 0.54930614433405484570; static const double p[] = { -0.16134119023996228053e+4, -0.99225929672236083313e+2, -0.96437492777225469787 }; static const double q[] = { 0.48402357071988688686e+4, 0.22337720718962312926e+4, 0.11274474380534949335e+3 }; double _DEFUN (tanh, (double), double x) { double f, res, g, P, Q, R; f = fabs (x); /* Check if the input is too big. */ if (f > BIGX) res = 1.0; else if (f > LN3_OVER2) res = 1.0 - 2.0 / (exp (2 * f) + 1.0); /* Check if the input is too small. */ else if (f < z_rooteps) res = f; /* Calculate the Taylor series. */ else { g = f * f; P = (p[2] * g + p[1]) * g + p[0]; Q = ((g + q[2]) * g + q[1]) * g + q[0]; R = g * (P / Q); res = f + f * R; } if (x < 0.0) res = -res; return (res); } #endif /* _DOUBLE_IS_32BITS */
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