116 lines
3.4 KiB
C
116 lines
3.4 KiB
C
/* tanh.c - math routines */
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/* Copyright 1992-1994 Wind River Systems, Inc. */
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/*
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modification history
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--------------------
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01f,09dec94,rhp fix man pages for hyperbolic fns.
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01e,05feb93,jdi doc changes based on kdl review.
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01d,02dec92,jdi doc tweaks.
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01c,28oct92,jdi documentation cleanup.
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01b,20sep92,smb documentation additions
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01a,08jul92,smb documentation.
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*/
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/*
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DESCRIPTION
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* Copyright (c) 1985 Regents of the University of California.
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms are permitted
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* provided that the above copyright notice and this paragraph are
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* duplicated in all such forms and that any documentation,
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* advertising materials, and other materials related to such
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* distribution and use acknowledge that the software was developed
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* by the University of California, Berkeley. The name of the
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* University may not be used to endorse or promote products derived
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* from this software without specific prior written permission.
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* THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
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* IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
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* WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
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*
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* All recipients should regard themselves as participants in an ongoing
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* research project and hence should feel obligated to report their
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* experiences (good or bad) with these elementary function codes, using
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* the sendbug(8) program, to the authors.
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*
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SEE ALSO: American National Standard X3.159-1989
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NOMANUAL
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*/
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#include "vxWorks.h"
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#include "math.h"
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/*******************************************************************************
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*
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* tanh - compute a hyperbolic tangent (ANSI)
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*
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* This routine returns the hyperbolic tangent of <x> in
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* double precision (IEEE double, 53 bits).
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*
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* INTERNAL:
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* Method:
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*
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* (1) Reduce <x> to non-negative by:
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*
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* tanh(-x) = - tanh(x)
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*
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* (2)
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* 0 < x <= 1.e-10 : tanh(x) := x
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*
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* -expm1(-2x)
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* 1.e-10 < x <= 1 : tanh(x) := --------------
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* expm1(-2x) + 2
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*
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* 2
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* 1 <= x <= 22.0 : tanh(x) := 1 - ---------------
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* expm1(2x) + 2
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* 22.0 < x <= INF : tanh(x) := 1.
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*
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* Note: 22 was chosen so that fl(1.0+2/(expm1(2*22)+2)) == 1.
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*
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* INCLUDE FILES: math.h
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*
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* RETURNS:
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* The double-precision hyperbolic tangent of <x>.
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*
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* Special cases:
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* If <x> is NaN, tanh() returns NaN.
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*
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* SEE ALSO: mathALib
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*
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* INTERNAL:
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* Coded in C by K.C. Ng, 1/8/85;
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* Revised by K.C. Ng on 2/8/85, 2/11/85, 3/7/85, 3/24/85.
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*/
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double tanh
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(
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double x /* number whose hyperbolic tangent is required */
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)
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{
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static double one=1.0, two=2.0, small = 1.0e-10, big = 1.0e10;
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double expm1(), t, copysign(), sign;
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int finite();
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#if !defined(vax)&&!defined(tahoe)
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if(x!=x) return(x); /* x is NaN */
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#endif /* !defined(vax)&&!defined(tahoe) */
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sign=copysign(one,x);
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x=copysign(x,one);
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if(x < 22.0)
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if( x > one )
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return(copysign(one-two/(expm1(x+x)+two),sign));
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else if ( x > small )
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{t= -expm1(-(x+x)); return(copysign(t/(two-t),sign));}
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else /* raise the INEXACT flag for non-zero x */
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{big+x; return(copysign(x,sign));}
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else if(finite(x))
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return (sign+1.0E-37); /* raise the INEXACT flag */
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else
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return(sign); /* x is +- INF */
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}
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