108 lines
2.7 KiB
C
108 lines
2.7 KiB
C
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/***
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*tanh.c - hyperbolic tangent
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*
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* Copyright (c) 1991-2001, Microsoft Corporation. All rights reserved.
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*
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*Purpose:
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*
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*Revision History:
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* 8-15-91 GDP written
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* 12-22-91 GDP support IEEE exceptions
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* 06-23-92 GDP tanh(denormal) now raises underflow exception (NCEG)
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* 02-06-95 JWM Mac merge
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* 05-17-99 PML Remove all Macintosh support.
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*
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*******************************************************************************/
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#include <math.h>
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#include <trans.h>
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/* constants */
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static double const EPS = 5.16987882845642297e-26; /* 2^(-53) / 2 */
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static double const XBIG = 1.90615474653984960096e+001; /* ln(2)(53+2)/2 */
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static double const C0 = 0.54930614433405484570; /* ln(3)/2 */
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/* constants for rational approximation */
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static double const p0 = -0.16134119023996228053e+4;
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static double const p1 = -0.99225929672236083313e+2;
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static double const p2 = -0.96437492777225469787e+0;
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static double const q0 = 0.48402357071988688686e+4;
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static double const q1 = 0.22337720718962312926e+4;
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static double const q2 = 0.11274474380534949335e+3;
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static double const q3 = 0.10000000000000000000e+1;
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#define Q(g) ((((g) + q2) * (g) + q1) * (g) + q0)
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#define R(g) ((((p2 * (g) + p1) * (g) + p0) * (g)) / Q(g))
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#if !defined(_M_PPC) && !defined(_M_AMD64)
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#pragma function(tanh)
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#endif
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/***
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*double tanh(double x) - hyperbolic tangent
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*
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*Purpose:
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* Compute the hyperbolic tangent of a number.
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* The algorithm (reduction / rational approximation) is
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* taken from Cody & Waite.
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*
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*Entry:
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*
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*Exit:
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*
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*Exceptions:
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* I P
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*******************************************************************************/
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double tanh(double x)
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{
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uintptr_t savedcw;
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double f,g;
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double result;
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/* save user fp control word */
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savedcw = _maskfp();
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if (IS_D_SPECIAL(x)){
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switch(_sptype(x)) {
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case T_PINF:
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RETURN(savedcw,1.0);
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case T_NINF:
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RETURN(savedcw,-1.0);
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case T_QNAN:
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return _handle_qnan1(OP_TANH, x, savedcw);
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default: //T_SNAN
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return _except1(FP_I,OP_TANH,x,_s2qnan(x),savedcw);
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}
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}
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if (x == 0.0) {
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// no precision exception
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RETURN(savedcw,x);
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}
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f = ABS(x);
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if (f > XBIG) {
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result = 1;
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}
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else if (f > C0) {
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result = 0.5 - 1.0 / (exp(f+f) + 1.0);
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result = result + result;
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}
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else if (f < EPS) {
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result = f;
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if (IS_D_DENORM(result)) {
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return _except1(FP_U | FP_P,OP_TANH,x,_add_exp(x, IEEE_ADJUST),savedcw);
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}
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}
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else {
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g = f * f;
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result = f + f * R(g);
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}
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if (x < 0)
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result = -result;
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RETURN_INEXACT1(OP_TANH,x,result,savedcw);
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}
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