/* FreeBSD: head/lib/msun/src/e_acos.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_acos.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;

#ifdef __i386__
/* XXX Work around the fact that gcc truncates long double constants on i386 */
static volatile double
pi1 =  3.14159265358979311600e+00,      /*  0x1.921fb54442d18p+1  */
pi2 =  1.22514845490862001043e-16;      /*  0x1.1a80000000000p-53 */
#define pi      ((long double)pi1 + pi2)
#else
static const long double
pi =  3.14159265358979323846264338327950280e+00L;
#endif

long double
acosl(long double x)
{
        union IEEEl2bits u;
        long double z,p,q,r,w,s,c,df;
        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) {
                if (expsign>0) return 0.0;      /* acos(1) = 0  */
                else return pi+2.0*pio2_lo;     /* acos(-1)= pi */
            }
            return (x-x)/(x-x);         /* acos(|x|>1) is NaN */
        }
        if(expt<BIAS-1) {       /* |x| < 0.5 */
            if(expt<ACOS_CONST) return pio2_hi+pio2_lo;/*x tiny: acosl=pi/2*/
            z = x*x;
            p = P(z);
            q = Q(z);
            r = p/q;
            return pio2_hi - (x - (pio2_lo-x*r));
        } else  if (expsign<0) {        /* x < -0.5 */
            z = (one+x)*0.5;
            p = P(z);
            q = Q(z);
            s = sqrtl(z);
            r = p/q;
            w = r*s-pio2_lo;
            return pi - 2.0*(s+w);
        } else {                        /* x > 0.5 */
            z = (one-x)*0.5;
            s = sqrtl(z);
            u.e = s;
            u.bits.manl = 0;
            df = u.e;
            c  = (z-df*df)/(s+df);
            p = P(z);
            q = Q(z);
            r = p/q;
            w = r*s+c;
            return 2.0*(df+w);
        }
}