expm1.c revision 3f54fd611f536639ec30dd53c48e5ec1897cc7d9
#if !_UWIN || _lib_expm1
void _STUB_expm1(){}
#else
/*
* Copyright (c) 1985, 1993
* The Regents of the University of California. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* 3. Neither the name of the University nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
#ifndef lint
#endif /* not lint */
/* EXPM1(X)
* RETURN THE EXPONENTIAL OF X MINUS ONE
* DOUBLE PRECISION (IEEE 53 BITS, VAX D FORMAT 56 BITS)
* CODED IN C BY K.C. NG, 1/19/85;
* REVISED BY K.C. NG on 2/6/85, 3/7/85, 3/21/85, 4/16/85.
*
* Required system supported functions:
* scalb(x,n)
* copysign(x,y)
* finite(x)
*
* Kernel function:
* exp__E(x,c)
*
* Method:
* 1. Argument Reduction: given the input x, find r and integer k such
* that
* x = k*ln2 + r, |r| <= 0.5*ln2 .
* r will be represented as r := z+c for better accuracy.
*
* 2. Compute EXPM1(r)=exp(r)-1 by
*
* EXPM1(r=z+c) := z + exp__E(z,c)
*
* 3. EXPM1(x) = 2^k * ( EXPM1(r) + 1-2^-k ).
*
* Remarks:
* 1. When k=1 and z < -0.25, we use the following formula for
* better accuracy:
* EXPM1(x) = 2 * ( (z+0.5) + exp__E(z,c) )
* 2. To avoid rounding error in 1-2^-k where k is large, we use
* EXPM1(x) = 2^k * { [z+(exp__E(z,c)-2^-k )] + 1 }
* when k>56.
*
* Special cases:
* EXPM1(INF) is INF, EXPM1(NaN) is NaN;
* EXPM1(-INF)= -1;
* for finite argument, only EXPM1(0)=0 is exact.
*
* Accuracy:
* EXPM1(x) returns the exact (exp(x)-1) nearly rounded. In a test run with
* 1,166,000 random arguments on a VAX, the maximum observed error was
* .872 ulps (units of the last place).
*
* Constants:
* The hexadecimal values are the intended ones for the following constants.
* The decimal values may be used, provided that the compiler will convert
* from decimal to binary accurately enough to produce the hexadecimal values
* shown.
*/
#include "mathimpl.h"
#ifdef vccast
#endif
extern double expm1(x)
double x;
{
int k;
static prec=56;
#else /* defined(vax)||defined(tahoe) */
static prec=53;
#endif /* defined(vax)||defined(tahoe) */
if(x!=x) return(x); /* x is NaN */
#endif /* !defined(vax)&&!defined(tahoe) */
if( x <= lnhuge ) {
if( x >= -40.0 ) {
/* argument reduction : x - k*ln2 */
if(k==0) return(z+__exp__E(z,c));
if(k==1)
if(z< -0.25)
else
/* end of k=1 */
else {
if(k<=prec)
else if(k<100)
else
return (scalb(x+z,k));
}
}
/* end of x > lnunfl */
else
/* expm1(-big#) rounded to -1 (inexact) */
if(finite(x))
/* expm1(-INF) is -1 */
else return(-one);
}
/* end of x < lnhuge */
else
/* expm1(INF) is INF, expm1(+big#) overflows to INF */
}
#endif