/* FreeBSD: head/lib/msun/src/e_asin.c 176451 2008-02-22 02:30:36Z das */
/*
 * ====================================================
 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
 *
 * Developed at SunSoft, a Sun Microsystems, Inc. business.
 * Permission to use, copy, modify, and distribute this
 * software is freely granted, provided that this notice 
 * is preserved.
 * ====================================================
 */

/*
 * See comments in e_asin.c.
 * Converted to long double by David Schultz <das@FreeBSD.ORG>.
 */

#include <float.h>

#include "invtrig.h"
#include "math.h"
#include "math_private.h"

static const long double
one =  1.00000000000000000000e+00,
huge = 1.000e+300;

long double
asinl(long double x)
{
        union IEEEl2bits u;
        long double t=0.0,w,p,q,c,r,s;
        int16_t expsign, expt;
        u.e = x;
        expsign = u.xbits.expsign;
        expt = expsign & 0x7fff;
        if(expt >= BIAS) {              /* |x|>= 1 */
                if(expt==BIAS && ((u.bits.manh&~LDBL_NBIT)|u.bits.manl)==0)
                    /* asin(1)=+-pi/2 with inexact */
                    return x*pio2_hi+x*pio2_lo; 
            return (x-x)/(x-x);         /* asin(|x|>1) is NaN */   
        } else if (expt<BIAS-1) {       /* |x|<0.5 */
            if(expt<ASIN_LINEAR) {      /* if |x| is small, asinl(x)=x */
                if(huge+x>one) return x;/* return x with inexact if x!=0*/
            }
            t = x*x;
            p = P(t);
            q = Q(t);
            w = p/q;
            return x+x*w;
        }
        /* 1> |x|>= 0.5 */
        w = one-fabsl(x);
        t = w*0.5;
        p = P(t);
        q = Q(t);
        s = sqrtl(t);
        if(u.bits.manh>=THRESH) {       /* if |x| is close to 1 */
            w = p/q;
            t = pio2_hi-(2.0*(s+s*w)-pio2_lo);
        } else {
            u.e = s;
            u.bits.manl = 0;
            w = u.e;
            c  = (t-w*w)/(s+w);
            r  = p/q;
            p  = 2.0*s*r-(pio2_lo-2.0*c);
            q  = pio4_hi-2.0*w;
            t  = pio4_hi-(p-q);
        }    
        if(expsign>0) return t; else return -t;    
}