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Diffstat (limited to 'sysdeps/generic/exp.c')
| -rw-r--r-- | sysdeps/generic/exp.c | 203 |
1 files changed, 203 insertions, 0 deletions
diff --git a/sysdeps/generic/exp.c b/sysdeps/generic/exp.c new file mode 100644 index 0000000000..9b4f045f82 --- /dev/null +++ b/sysdeps/generic/exp.c @@ -0,0 +1,203 @@ +/* + * 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); +} |