asinh.c

VXWORKS源代码

/* asinh.c - math routines */

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

/*
modification history
--------------------
01c,14oct92,jdi  made asinh() nomanual.
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)	/* VAX/TAHOE D format */
#ifdef vax
#define _0x(A,B)	0x/**/A/**/B
#else	/* vax */
#define _0x(A,B)	0x/**/B/**/A
#endif	/* vax */
/* static double */
/* ln2hi  =  6.9314718055829871446E-1    , Hex  2^  0   *  .B17217F7D00000 */
/* ln2lo  =  1.6465949582897081279E-12   ; Hex  2^-39   *  .E7BCD5E4F1D9CC */
static long     ln2hix[] = { _0x(7217,4031), _0x(0000,f7d0)};
static long     ln2lox[] = { _0x(bcd5,2ce7), _0x(d9cc,e4f1)};
#define    ln2hi    (*(double*)ln2hix)
#define    ln2lo    (*(double*)ln2lox)
#else	/* defined(vax)||defined(tahoe) */
static double
ln2hi  =  6.9314718036912381649E-1    , /*Hex  2^ -1   *  1.62E42FEE00000 */
ln2lo  =  1.9082149292705877000E-10   ; /*Hex  2^-33   *  1.A39EF35793C76 */
#endif	/* defined(vax)||defined(tahoe) */

/*****************************************************************************
* asinh	- compute the inverse hyperbolic sine of <x>
*
* ASINH(X)
* RETURN THE INVERSE HYPERBOLIC SINE OF X
* DOUBLE PRECISION (VAX D format 56 bits, IEEE DOUBLE 53 BITS)
* CODED IN C BY K.C. NG, 2/16/85;
* REVISED BY K.C. NG on 3/7/85, 3/24/85, 4/16/85.
*
* Required system supported functions are copysign(x,y) and sqrt(x).
*
* Required kernel function is log1p(x) 		...return log(1+x)
*
* Method :
* Based on
* .CS
*    asinh(x) = sign(x) * log [ |x| + sqrt(x*x+1) ]
* .CE
* we have
* .CS
*    asinh(x) := x  if  1+x*x=1,
*    := sign(x)*(log1p(x)+ln2))	 if sqrt(1+x*x)=x, else
*    := sign(x)*log1p(|x| + |x|/(1/|x| + sqrt(1+(1/|x|)^2)) )
* .CE
*
* asinh(x) returns the exact inverse hyperbolic sine of x nearly rounded.
* In a test run with 52,000 random arguments on a VAX, the maximum
* observed error was 1.58 ulps (units in the last place).
* The hexadecimal values are the intended ones for the following constants.
* The decimal values may be used, provided that the compiler will convert
* from decimal to binary accurately enough to produce the hexadecimal values
* shown.
*
* NOMANUAL
*/

double asinh(x)
double x;
{
	double copysign(),log1p(),sqrt(),t,s;
	static double small=1.0E-10,	/* fl(1+small*small) == 1 */
		      big  =1.0E20,	/* fl(1+big) == big */
		      one  =1.0   ;

#if !defined(vax)&&!defined(tahoe)
	if(x!=x) return(x);	/* x is NaN */
#endif	/* !defined(vax)&&!defined(tahoe) */
	if((t=copysign(x,one))>small)
	    if(t<big) {
	     	s=one/t; return(copysign(log1p(t+t/(s+sqrt(one+s*s))),x)); }
	    else	/* if |x| > big */
		{s=log1p(t)+ln2lo; return(copysign(s+ln2hi,x));}
	else	/* if |x| < small */
	    return(x);
}