e_coshf.c

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/* e_coshf.c -- float version of e_cosh.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 volatile float huge = 1.0e30;
static const float one = 1.0, half=0.5;

float
coshf(float x)
{   
    float t,w;
    int32_t ix;

    GET_FLOAT_WORD(ix,x);
    ix &= 0x7fffffff;

    /* x is INF or NaN */
    if(ix>=0x7f800000) return x*x;  

    /* |x| in [0,0.5*ln2], return 1+expm1(|x|)^2/(2*exp(|x|)) */
    if(ix<0x3eb17218) {
        t = expm1f(fabsf(x));
        w = one+t;
        if (ix<0x24000000) return w;    /* cosh(tiny) = 1 */
        return one+(t*t)/(w+w);
    }

    /* |x| in [0.5*ln2,22], return (exp(|x|)+1/exp(|x|)/2; */
    if (ix < 0x41b00000) {
        t = expf(fabsf(x));
        return half*t+half/t;
    }

    /* |x| in [22, log(maxdouble)] return half*exp(|x|) */
    if (ix < 0x42b17180)  return half*expf(fabsf(x));

    /* |x| in [log(maxdouble), overflowthresold] */
    if (ix<=0x42b2d4fc) {
        w = expf(half*fabsf(x));
        t = half*w;
        return t*w;
    }

    /* |x| > overflowthresold, cosh(x) overflow */
    return huge*huge;
}