Quelle e_sinh.c Sprache: C

/*
* Copyright (c) 1998, 2001, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation.  Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*/

/* __ieee754_sinh(x)
* Method :
* mathematically sinh(x) if defined to be (exp(x)-exp(-x))/2
*      1. Replace x by |x| (sinh(-x) = -sinh(x)).
*      2.
*                                                  E + E/(E+1)
*          0        <= x <= 22     :  sinh(x) := --------------, E=expm1(x)
*                                                      2
*
*          22       <= x <= lnovft :  sinh(x) := exp(x)/2
*          lnovft   <= x <= ln2ovft:  sinh(x) := exp(x/2)/2 * exp(x/2)
*          ln2ovft  <  x           :  sinh(x) := x*shuge (overflow)
*
* Special cases:
*      sinh(x) is |x| if x is +INF, -INF, or NaN.
*      only sinh(0)=0 is exact for finite x.
*/

#include "fdlibm.h"

#ifdef __STDC__
static const double one = 1.0, shuge = 1.0e307;
#else
static double one = 1.0, shuge = 1.0e307;
#endif

#ifdef __STDC__
        double __ieee754_sinh(double x)
#else
        double __ieee754_sinh(x)
        double x;
#endif
{
        double t,w,h;
        int ix,jx;
        unsigned lx;

    /* High word of |x|. */
        jx = __HI(x);
        ix = jx&0x7fffffff;

    /* x is INF or NaN */
        if(ix>=0x7ff00000) return x+x;

        h = 0.5;
        if (jx<0) h = -h;
    /* |x| in [0,22], return sign(x)*0.5*(E+E/(E+1))) */
        if (ix < 0x40360000) {          /* |x|<22 */
            if (ix<0x3e300000)          /* |x|<2**-28 */
                if(shuge+x>one) return x;/* sinh(tiny) = tiny with inexact */
            t = expm1(fabs(x));
            if(ix<0x3ff00000) return h*(2.0*t-t*t/(t+one));
            return h*(t+t/(t+one));
        }

    /* |x| in [22, log(maxdouble)] return 0.5*exp(|x|) */
        if (ix < 0x40862E42)  return h*__ieee754_exp(fabs(x));

    /* |x| in [log(maxdouble), overflowthresold] */
        lx = *( (((*(unsigned*)&one)>>29)) + (unsigned*)&x);
        if (ix<0x408633CE || ((ix==0x408633ce)&&(lx<=(unsigned)0x8fb9f87d))) {
            w = __ieee754_exp(0.5*fabs(x));
            t = h*w;
            return t*w;
        }

    /* |x| > overflowthresold, sinh(x) overflow */
        return x*shuge;
}

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