4.4BSD/usr/src/lib/libm/common_source/exp.c
/*
* 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
* documentation and/or other materials provided with the distribution.
* 3. All advertising materials mentioning features or use of this software
* must display the following acknowledgement:
* This product includes software developed by the University of
* California, Berkeley and its contributors.
* 4. 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
static char sccsid[] = "@(#)exp.c 8.1 (Berkeley) 6/4/93";
#endif /* not lint */
/* EXP(X)
* RETURN THE EXPONENTIAL OF X
* 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, 2/15/85, 3/7/85, 3/24/85, 4/16/85, 6/14/86.
*
* Required system supported functions:
* scalb(x,n)
* copysign(x,y)
* finite(x)
*
* 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 exp(r) by
*
* exp(r) = 1 + r + r*R1/(2-R1),
* where
* R1 = x - x^2*(p1+x^2*(p2+x^2*(p3+x^2*(p4+p5*x^2)))).
*
* 3. exp(x) = 2^k * exp(r) .
*
* Special cases:
* exp(INF) is INF, exp(NaN) is NaN;
* exp(-INF)= 0;
* for finite argument, only exp(0)=1 is exact.
*
* Accuracy:
* exp(x) returns the exponential of x nearly rounded. In a test run
* with 1,156,000 random arguments on a VAX, the maximum observed
* error was 0.869 ulps (units in 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"
vc(ln2hi, 6.9314718055829871446E-1 ,7217,4031,0000,f7d0, 0, .B17217F7D00000)
vc(ln2lo, 1.6465949582897081279E-12 ,bcd5,2ce7,d9cc,e4f1, -39, .E7BCD5E4F1D9CC)
vc(lnhuge, 9.4961163736712506989E1 ,ec1d,43bd,9010,a73e, 7, .BDEC1DA73E9010)
vc(lntiny,-9.5654310917272452386E1 ,4f01,c3bf,33af,d72e, 7,-.BF4F01D72E33AF)
vc(invln2, 1.4426950408889634148E0 ,aa3b,40b8,17f1,295c, 1, .B8AA3B295C17F1)
vc(p1, 1.6666666666666602251E-1 ,aaaa,3f2a,a9f1,aaaa, -2, .AAAAAAAAAAA9F1)
vc(p2, -2.7777777777015591216E-3 ,0b60,bc36,ec94,b5f5, -8,-.B60B60B5F5EC94)
vc(p3, 6.6137563214379341918E-5 ,b355,398a,f15f,792e, -13, .8AB355792EF15F)
vc(p4, -1.6533902205465250480E-6 ,ea0e,b6dd,5f84,2e93, -19,-.DDEA0E2E935F84)
vc(p5, 4.1381367970572387085E-8 ,bb4b,3431,2683,95f5, -24, .B1BB4B95F52683)
#ifdef vccast
#define ln2hi vccast(ln2hi)
#define ln2lo vccast(ln2lo)
#define lnhuge vccast(lnhuge)
#define lntiny vccast(lntiny)
#define invln2 vccast(invln2)
#define p1 vccast(p1)
#define p2 vccast(p2)
#define p3 vccast(p3)
#define p4 vccast(p4)
#define p5 vccast(p5)
#endif
ic(p1, 1.6666666666666601904E-1, -3, 1.555555555553E)
ic(p2, -2.7777777777015593384E-3, -9, -1.6C16C16BEBD93)
ic(p3, 6.6137563214379343612E-5, -14, 1.1566AAF25DE2C)
ic(p4, -1.6533902205465251539E-6, -20, -1.BBD41C5D26BF1)
ic(p5, 4.1381367970572384604E-8, -25, 1.6376972BEA4D0)
ic(ln2hi, 6.9314718036912381649E-1, -1, 1.62E42FEE00000)
ic(ln2lo, 1.9082149292705877000E-10,-33, 1.A39EF35793C76)
ic(lnhuge, 7.1602103751842355450E2, 9, 1.6602B15B7ECF2)
ic(lntiny,-7.5137154372698068983E2, 9, -1.77AF8EBEAE354)
ic(invln2, 1.4426950408889633870E0, 0, 1.71547652B82FE)
double exp(x)
double x;
{
double z,hi,lo,c;
int k;
#if !defined(vax)&&!defined(tahoe)
if(x!=x) return(x); /* x is NaN */
#endif /* !defined(vax)&&!defined(tahoe) */
if( x <= lnhuge ) {
if( x >= lntiny ) {
/* argument reduction : x --> x - k*ln2 */
k=invln2*x+copysign(0.5,x); /* k=NINT(x/ln2) */
/* express x-k*ln2 as hi-lo and let x=hi-lo rounded */
hi=x-k*ln2hi;
x=hi-(lo=k*ln2lo);
/* return 2^k*[1+x+x*c/(2+c)] */
z=x*x;
c= x - z*(p1+z*(p2+z*(p3+z*(p4+z*p5))));
return scalb(1.0+(hi-(lo-(x*c)/(2.0-c))),k);
}
/* end of x > lntiny */
else
/* exp(-big#) underflows to zero */
if(finite(x)) return(scalb(1.0,-5000));
/* exp(-INF) is zero */
else return(0.0);
}
/* end of x < lnhuge */
else
/* exp(INF) is INF, exp(+big#) overflows to INF */
return( finite(x) ? scalb(1.0,5000) : x);
}
/* returns exp(r = x + c) for |c| < |x| with no overlap. */
double __exp__D(x, c)
double x, c;
{
double z,hi,lo, t;
int k;
#if !defined(vax)&&!defined(tahoe)
if (x!=x) return(x); /* x is NaN */
#endif /* !defined(vax)&&!defined(tahoe) */
if ( x <= lnhuge ) {
if ( x >= lntiny ) {
/* argument reduction : x --> x - k*ln2 */
z = invln2*x;
k = z + copysign(.5, x);
/* express (x+c)-k*ln2 as hi-lo and let x=hi-lo rounded */
hi=(x-k*ln2hi); /* Exact. */
x= hi - (lo = k*ln2lo-c);
/* return 2^k*[1+x+x*c/(2+c)] */
z=x*x;
c= x - z*(p1+z*(p2+z*(p3+z*(p4+z*p5))));
c = (x*c)/(2.0-c);
return scalb(1.+(hi-(lo - c)), k);
}
/* end of x > lntiny */
else
/* exp(-big#) underflows to zero */
if(finite(x)) return(scalb(1.0,-5000));
/* exp(-INF) is zero */
else return(0.0);
}
/* end of x < lnhuge */
else
/* exp(INF) is INF, exp(+big#) overflows to INF */
return( finite(x) ? scalb(1.0,5000) : x);
}