/* ef_acosh.c -- float version of e_acosh.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 = 1.0, ln2 = 6.9314718246e-01; /* 0x3f317218 */

float
acoshf(float x)
{
    float t;
    __int32_t hx;
    GET_FLOAT_WORD(hx, x);
    if (hx < 0x3f800000) { /* x < 1 */
        return __math_invalidf(x);
    } else if (hx >= 0x4d800000) { /* x > 2**28 */
        if (!FLT_UWORD_IS_FINITE(hx)) { /* x is inf of NaN */
            return x + x;
        } else
            return logf(x) + ln2; /* acosh(huge)=log(2x) */
    } else if (hx == 0x3f800000) {
        return 0.0; /* acosh(1) = 0 */
    } else if (hx > 0x40000000) { /* 2**28 > x > 2 */
        t = x * x;
        return logf((float)2.0 * x - one / (x + sqrtf(t - one)));
    } else { /* 1<x<2 */
        t = x - one;
        return log1pf(t + sqrtf((float)2.0 * t + t * t));
    }
}
