#ifndef lint
static char sccsid[] = "@(#)asin.c 1.1 92/07/30 SMI";
#endif
/*
* Copyright (c) 1987 by Sun Microsystems, Inc.
*/
/* asin(x)
* Code originated from 4.3bsd.
* Modified by K.C. Ng for SUN 4.0 libm.
* Method :
*
* asin(x) = atan2(x,sqrt(1-x*x)); for better accuracy, 1-x*x is
* computed as follows
* 1-x*x if x < 0.5,
* 2*(1-|x|)-(1-|x|)*(1-|x|) if x >= 0.5.
*
* Special cases:
* if x is NaN, return x itself;
* if |x|>1, return NaN with invalid signal.
*
*/
#include <math.h>
#include "libm.h"
double asin(x)
double x;
{
double t,w;
w = fabs(x);
if (x!=x)
return x+x;
else if(w <= 0.5) {
if(w<1.0e-9) {dummy(1.0e9+w); return x;} else
return atan(x/sqrt(1.-x*x));
}
else if(w < 1.0) {
t = 1.0-w;
w = t+t;
return atan(x/sqrt(w-t*t));
}
else if(w == 1.0)
return atan2(x,0.0); /* asin(+-1) = +- PI/2 */
else { /* |x| > 1 create invalid signal */
return SVID_libm_err(x,x,2);
}
}
static dummy(x)
double x;
{
return 1;
}
