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));
    }
}