source: asp3_tinet_ecnl_rx/trunk/musl-1.1.18/src/math/acosl.c@ 337

/* origin: FreeBSD /usr/src/lib/msun/src/e_acosl.c */
/*
 * ====================================================
 * 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 acos.c.
 * Converted to long double by David Schultz <das@FreeBSD.ORG>.
 */

#include "libm.h"

#if LDBL_MANT_DIG == 53 && LDBL_MAX_EXP == 1024
long double acosl(long double x)
{
        return acos(x);
}
#elif (LDBL_MANT_DIG == 64 || LDBL_MANT_DIG == 113) && LDBL_MAX_EXP == 16384
#include "__invtrigl.h"
#if LDBL_MANT_DIG == 64
#define CLEARBOTTOM(u) (u.i.m &= -1ULL << 32)
#elif LDBL_MANT_DIG == 113
#define CLEARBOTTOM(u) (u.i.lo = 0)
#endif

long double acosl(long double x)
{
        union ldshape u = {x};
        long double z, s, c, f;
        uint16_t e = u.i.se & 0x7fff;

        /* |x| >= 1 or nan */
        if (e >= 0x3fff) {
                if (x == 1)
                        return 0;
                if (x == -1)
                        return 2*pio2_hi + 0x1p-120f;
                return 0/(x-x);
        }
        /* |x| < 0.5 */
        if (e < 0x3fff - 1) {
                if (e < 0x3fff - LDBL_MANT_DIG - 1)
                        return pio2_hi + 0x1p-120f;
                return pio2_hi - (__invtrigl_R(x*x)*x - pio2_lo + x);
        }
        /* x < -0.5 */
        if (u.i.se >> 15) {
                z = (1 + x)*0.5;
                s = sqrtl(z);
                return 2*(pio2_hi - (__invtrigl_R(z)*s - pio2_lo + s));
        }
        /* x > 0.5 */
        z = (1 - x)*0.5;
        s = sqrtl(z);
        u.f = s;
        CLEARBOTTOM(u);
        f = u.f;
        c = (z - f*f)/(s + f);
        return 2*(__invtrigl_R(z)*s + c + f);
}
#endif