cosh.c

VXWORKS源代码

/* cosh.c - hyperbolic routines */

/* Copyright 1992-1993 Wind River Systems, Inc. */

/*
modification history
--------------------
01e,05feb93,jdi  doc changes based on kdl review.
01d,02dec92,jdi  doc tweaks.
01c,28oct92,jdi  documentation cleanup.
01b,20sep92,smb  documentation additions
01a,08jul92,smb  documentation
*/

/*
DESCRIPTION
* Copyright (c) 1985 Regents of the University of California.
* All rights reserved.
*
* Redistribution and use in source and binary forms are permitted
* provided that the above copyright notice and this paragraph are
* duplicated in all such forms and that any documentation,
* advertising materials, and other materials related to such
* distribution and use acknowledge that the software was developed
* by the University of California, Berkeley.  The name of the
* University may not be used to endorse or promote products derived
* from this software without specific prior written permission.
* THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
* IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
* WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
*
* All recipients should regard themselves as participants in an ongoing
* research project and hence should feel obligated to report their
* experiences (good or bad) with these elementary function codes, using
* the sendbug(8) program, to the authors.
*
SEE ALSO: American National Standard X3.159-1989
NOMANUAL
*/

#include "vxWorks.h"
#include "math.h"

#if defined(vax)||defined(tahoe)
#ifdef vax
#define _0x(A,B)	0x/**/A/**/B
#else	/* vax */
#define _0x(A,B)	0x/**/B/**/A
#endif	/* vax */
/* static double  */
/* mln2hi =  8.8029691931113054792E1     , Hex  2^  7   *  .B00F33C7E22BDB */
/* mln2lo = -4.9650192275318476525E-16   , Hex  2^-50   * -.8F1B60279E582A */
/* lnovfl =  8.8029691931113053016E1     ; Hex  2^  7   *  .B00F33C7E22BDA */
static long    mln2hix[] = { _0x(0f33,43b0), _0x(2bdb,c7e2)};
static long    mln2lox[] = { _0x(1b60,a70f), _0x(582a,279e)};
static long    lnovflx[] = { _0x(0f33,43b0), _0x(2bda,c7e2)};
#define   mln2hi    (*(double*)mln2hix)
#define   mln2lo    (*(double*)mln2lox)
#define   lnovfl    (*(double*)lnovflx)
#else	/* defined(vax)||defined(tahoe) */
static double
mln2hi =  7.0978271289338397310E2     , /*Hex  2^ 10   *  1.62E42FEFA39EF */
mln2lo =  2.3747039373786107478E-14   , /*Hex  2^-45   *  1.ABC9E3B39803F */
lnovfl =  7.0978271289338397310E2     ; /*Hex  2^  9   *  1.62E42FEFA39EF */
#endif	/* defined(vax)||defined(tahoe) */

#if defined(vax)||defined(tahoe)
static max = 126                      ;
#else	/* defined(vax)||defined(tahoe) */
static max = 1023                     ;
#endif	/* defined(vax)||defined(tahoe) */

/*******************************************************************************
*
* cosh - compute a hyperbolic cosine (ANSI)
*
* This routine returns the hyperbolic cosine of <x> in
* double precision (IEEE double, 53 bits).
*
* A range error occurs if <x> is too large.
*
* INTERNAL:
* Method:
* (1) Replace <x> by |x|.
* (2)
*                                                 [ exp(x) - 1 ]^2
*     0        <= x <= 0.3465  :  cosh(x) := 1 + -------------------
*                                                    2*exp(x)
*
*                                            exp(x) +  1/exp(x)
*     0.3465   <= x <= 22      :  cosh(x) := -------------------
*                                                    2
*     22       <= x <= lnovfl  :  cosh(x) := exp(x)/2
*     lnovfl   <= x <= lnovfl+log(2)
*                              :  cosh(x) := exp(x)/2 (avoid overflow)
*     log(2)+lnovfl <  x <  INF:  overflow to INF
*
*         Note: .3465 is a number near one half of ln2.
*
* INCLUDE FILES: math.h
*
* RETURNS:
* The double-precision hyperbolic cosine of <x>.
*
* Special cases:
*     If <x> is +INF, -INF, or NaN, cosh() returns <x>.
*
* SEE ALSO: mathALib
*
* INTERNAL:
* Coded in C by K.C. Ng, 1/8/85;
* Revised by K.C. Ng on 2/8/85, 2/23/85, 3/7/85, 3/29/85, 4/16/85.
*/

double cosh
    (
    double x	/* value to compute the hyperbolic cosine of */
    )

    {
	static double half=1.0/2.0,one=1.0, small=1.0E-18; /* fl(1+small)==1 */
	double scalb(),copysign(),exp(),exp__E(),t;

#if !defined(vax)&&!defined(tahoe)
	if(x!=x) return(x);	/* x is NaN */
#endif	/* !defined(vax)&&!defined(tahoe) */
	if((x=copysign(x,one)) <= 22)
	    if(x<0.3465)
		if(x<small) return(one+x);
		else {t=x+exp__E(x,0.0);x=t+t; return(one+t*t/(2.0+x)); }

	    else /* for x lies in [0.3465,22] */
	        { t=exp(x); return((t+one/t)*half); }

	if( lnovfl <= x && x <= (lnovfl+0.7))
        /* for x lies in [lnovfl, lnovfl+ln2], decrease x by ln(2^(max+1))
         * and return 2^max*exp(x) to avoid unnecessary overflow
         */
	    return(scalb(exp((x-mln2hi)-mln2lo), max));

	else
	    return(exp(x)*half);	/* for large x,  cosh(x)=exp(x)/2 */
    }