/* origin: FreeBSD /usr/src/lib/msun/src/e_acosf.c */
/*
 * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
 */
/*
 * ====================================================
 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
 *
 * Developed at SunPro, a Sun Microsystems, Inc. business.
 * Permission to use, copy, modify, and distribute this
 * software is freely granted, provided that this notice
 * is preserved.
 * ====================================================
 */

#include "libm.h"

static const float
    pio2_hi = 1.5707962513e+00, /* 0x3fc90fda */
    pio2_lo = 7.5497894159e-08, /* 0x33a22168 */
    pS0 = 1.6666586697e-01,
    pS1 = -4.2743422091e-02,
    pS2 = -8.6563630030e-03,
    qS1 = -7.0662963390e-01;

static float R(float z)
{
    float_t p, q;
    p = z * (pS0 + z * (pS1 + z * pS2));
    q = 1.0f + z * qS1;
    return p / q;
}

float acosf(float x)
{
    float z, w, s, c, df;
    uint32_t hx, ix;

    GET_FLOAT_WORD(hx, x);
    ix = hx & 0x7fffffff;
    /* |x| >= 1 or nan */
    if (ix >= 0x3f800000)
    {
        if (ix == 0x3f800000)
        {
            if (hx >> 31)
                return 2 * pio2_hi + 0x1p-120f;
            return 0;
        }
        return 0 / (x - x);
    }
    /* |x| < 0.5 */
    if (ix < 0x3f000000)
    {
        if (ix <= 0x32800000) /* |x| < 2**-26 */
            return pio2_hi + 0x1p-120f;
        return pio2_hi - (x - (pio2_lo - x * R(x * x)));
    }
    /* x < -0.5 */
    if (hx >> 31)
    {
        z = (1 + x) * 0.5f;
        s = sqrtf(z);
        w = R(z) * s - pio2_lo;
        return 2 * (pio2_hi - (s + w));
    }
    /* x > 0.5 */
    z = (1 - x) * 0.5f;
    s = sqrtf(z);
    GET_FLOAT_WORD(hx, s);
    SET_FLOAT_WORD(df, hx & 0xfffff000);
    c = (z - df * df) / (s + df);
    w = R(z) * s + c;
    return 2 * (df + w);
}
