/* ef_acos.c -- float version of e_acos.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 "fdlibm.h"

static const float one = 1.0000000000e+00, /* 0x3F800000 */
    pi = 3.1415925026e+00, /* 0x40490fda */
    pio2_hi = 1.5707962513e+00, /* 0x3fc90fda */
    pio2_lo = 7.5497894159e-08, /* 0x33a22168 */
    pS0 = 1.6666667163e-01, /* 0x3e2aaaab */
    pS1 = -3.2556581497e-01, /* 0xbea6b090 */
    pS2 = 2.0121252537e-01, /* 0x3e4e0aa8 */
    pS3 = -4.0055535734e-02, /* 0xbd241146 */
    pS4 = 7.9153501429e-04, /* 0x3a4f7f04 */
    pS5 = 3.4793309169e-05, /* 0x3811ef08 */
    qS1 = -2.4033949375e+00, /* 0xc019d139 */
    qS2 = 2.0209457874e+00, /* 0x4001572d */
    qS3 = -6.8828397989e-01, /* 0xbf303361 */
    qS4 = 7.7038154006e-02; /* 0x3d9dc62e */

float
acosf(float x)
{
    float z, p, q, r, w, s, c, df;
    __int32_t hx, ix;
    GET_FLOAT_WORD(hx, x);
    ix = hx & 0x7fffffff;
    if (ix == 0x3f800000) { /* |x|==1 */
        if (hx > 0)
            return 0.0; /* acos(1) = 0  */
        else
            return pi + (float)2.0 * pio2_lo; /* acos(-1)= pi */
    } else if (ix > 0x3f800000) { /* |x| >= 1 */
        return __math_invalidf(x); /* acos(|x|>1) is NaN */
    }
    if (ix < 0x3f000000) { /* |x| < 0.5 */
        if (ix <= 0x23000000)
            return pio2_hi + pio2_lo; /*if|x|<2**-57*/
        z = x * x;
        p = z * (pS0 + z * (pS1 + z * (pS2 + z * (pS3 + z * (pS4 + z * pS5)))));
        q = one + z * (qS1 + z * (qS2 + z * (qS3 + z * qS4)));
        r = p / q;
        return pio2_hi - (x - (pio2_lo - x * r));
    } else if (hx < 0) { /* x < -0.5 */
        z = (one + x) * (float)0.5;
        p = z * (pS0 + z * (pS1 + z * (pS2 + z * (pS3 + z * (pS4 + z * pS5)))));
        q = one + z * (qS1 + z * (qS2 + z * (qS3 + z * qS4)));
        s = sqrtf(z);
        r = p / q;
        w = r * s - pio2_lo;
        return pi - (float)2.0 * (s + w);
    } else { /* x > 0.5 */
        __int32_t idf;
        z = (one - x) * (float)0.5;
        s = sqrtf(z);
        df = s;
        GET_FLOAT_WORD(idf, df);
        SET_FLOAT_WORD(df, idf & 0xfffff000);
        c = (z - df * df) / (s + df);
        p = z * (pS0 + z * (pS1 + z * (pS2 + z * (pS3 + z * (pS4 + z * pS5)))));
        q = one + z * (qS1 + z * (qS2 + z * (qS3 + z * qS4)));
        r = p / q;
        w = r * s + c;
        return (float)2.0 * (df + w);
    }
}

_MATH_ALIAS_f_f(acos)