src/math/e_acoshf.c


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/* e_acoshf.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 <math.h>
#include "math_private.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 (x-x)/(x-x);
        } else if(hx >=0x4d800000) {    /* x > 2**28 */
            if(hx >=0x7f800000) {       /* 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));
        }
}