/* 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
