57 lines
1.3 KiB
C
57 lines
1.3 KiB
C
|
|
#ifndef lint
|
|
static char sccsid[] = "@(#)cosh.c 1.1 92/07/30 SMI";
|
|
#endif
|
|
|
|
/*
|
|
* Copyright (c) 1986 by Sun Microsystems, Inc.
|
|
*/
|
|
|
|
/* cosh(x)
|
|
* Code originated from 4.3bsd.
|
|
* Modified by K.C. Ng for SUN 4.0 libm.
|
|
* Method :
|
|
* 1. Replace x by |x| (cosh(x) = cosh(-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 <= lnovft : cosh(x) := exp(x)/2
|
|
* lnovft <= x < INF : cosh(x) := scalbn(exp(x-1024*ln2),1023)
|
|
*
|
|
* Note: .3465 is a number near one half of ln2.
|
|
*
|
|
* Special cases:
|
|
* cosh(x) is |x| if x is +INF, -INF, or NaN.
|
|
* only cosh(0)=1 is exact for finite x.
|
|
*/
|
|
|
|
#include <math.h>
|
|
#include "libm.h"
|
|
|
|
double cosh(x)
|
|
double x;
|
|
{
|
|
double t,w;
|
|
w = fabs(x);
|
|
if(!finite(w)) return w+w; /* x is INF or NaN */
|
|
if( w < 0.3465 ) {
|
|
t = expm1(w);
|
|
w = 1.0+t;
|
|
if(w!=1.0) w = 1.0+(t*t)/(w+w);
|
|
return w;
|
|
} else if (w < 22.) {
|
|
t = exp(w);
|
|
return 0.5*(t+1.0/t);
|
|
} else if (w <= lnovft) return 0.5*exp(w);
|
|
else {
|
|
w = scalbn(exp((w-1024*ln2hi)-1024*ln2lo), 1023);
|
|
if(!finite(w)) w = SVID_libm_err(x,x,5);
|
|
return w;
|
|
}
|
|
}
|