n_exp.c revision 1.6
1 /* $NetBSD: n_exp.c,v 1.6 2002/06/15 00:10:17 matt Exp $ */ 2 /* 3 * Copyright (c) 1985, 1993 4 * The Regents of the University of California. All rights reserved. 5 * 6 * Redistribution and use in source and binary forms, with or without 7 * modification, are permitted provided that the following conditions 8 * are met: 9 * 1. Redistributions of source code must retain the above copyright 10 * notice, this list of conditions and the following disclaimer. 11 * 2. Redistributions in binary form must reproduce the above copyright 12 * notice, this list of conditions and the following disclaimer in the 13 * documentation and/or other materials provided with the distribution. 14 * 3. All advertising materials mentioning features or use of this software 15 * must display the following acknowledgement: 16 * This product includes software developed by the University of 17 * California, Berkeley and its contributors. 18 * 4. Neither the name of the University nor the names of its contributors 19 * may be used to endorse or promote products derived from this software 20 * without specific prior written permission. 21 * 22 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 23 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 24 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 25 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 26 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 27 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 28 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 29 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 30 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 31 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32 * SUCH DAMAGE. 33 */ 34 35 #ifndef lint 36 #if 0 37 static char sccsid[] = "@(#)exp.c 8.1 (Berkeley) 6/4/93"; 38 #endif 39 #endif /* not lint */ 40 41 /* EXP(X) 42 * RETURN THE EXPONENTIAL OF X 43 * DOUBLE PRECISION (IEEE 53 bits, VAX D FORMAT 56 BITS) 44 * CODED IN C BY K.C. NG, 1/19/85; 45 * REVISED BY K.C. NG on 2/6/85, 2/15/85, 3/7/85, 3/24/85, 4/16/85, 6/14/86. 46 * 47 * Required system supported functions: 48 * scalb(x,n) 49 * copysign(x,y) 50 * finite(x) 51 * 52 * Method: 53 * 1. Argument Reduction: given the input x, find r and integer k such 54 * that 55 * x = k*ln2 + r, |r| <= 0.5*ln2 . 56 * r will be represented as r := z+c for better accuracy. 57 * 58 * 2. Compute exp(r) by 59 * 60 * exp(r) = 1 + r + r*R1/(2-R1), 61 * where 62 * R1 = x - x^2*(p1+x^2*(p2+x^2*(p3+x^2*(p4+p5*x^2)))). 63 * 64 * 3. exp(x) = 2^k * exp(r) . 65 * 66 * Special cases: 67 * exp(INF) is INF, exp(NaN) is NaN; 68 * exp(-INF)= 0; 69 * for finite argument, only exp(0)=1 is exact. 70 * 71 * Accuracy: 72 * exp(x) returns the exponential of x nearly rounded. In a test run 73 * with 1,156,000 random arguments on a VAX, the maximum observed 74 * error was 0.869 ulps (units in the last place). 75 * 76 * Constants: 77 * The hexadecimal values are the intended ones for the following constants. 78 * The decimal values may be used, provided that the compiler will convert 79 * from decimal to binary accurately enough to produce the hexadecimal values 80 * shown. 81 */ 82 83 #define _LIBM_STATIC 84 #include "mathimpl.h" 85 86 vc(ln2hi, 6.9314718055829871446E-1 ,7217,4031,0000,f7d0, 0, .B17217F7D00000) 87 vc(ln2lo, 1.6465949582897081279E-12 ,bcd5,2ce7,d9cc,e4f1, -39, .E7BCD5E4F1D9CC) 88 vc(lnhuge, 9.4961163736712506989E1 ,ec1d,43bd,9010,a73e, 7, .BDEC1DA73E9010) 89 vc(lntiny,-9.5654310917272452386E1 ,4f01,c3bf,33af,d72e, 7,-.BF4F01D72E33AF) 90 vc(invln2, 1.4426950408889634148E0 ,aa3b,40b8,17f1,295c, 1, .B8AA3B295C17F1) 91 vc(p1, 1.6666666666666602251E-1 ,aaaa,3f2a,a9f1,aaaa, -2, .AAAAAAAAAAA9F1) 92 vc(p2, -2.7777777777015591216E-3 ,0b60,bc36,ec94,b5f5, -8,-.B60B60B5F5EC94) 93 vc(p3, 6.6137563214379341918E-5 ,b355,398a,f15f,792e, -13, .8AB355792EF15F) 94 vc(p4, -1.6533902205465250480E-6 ,ea0e,b6dd,5f84,2e93, -19,-.DDEA0E2E935F84) 95 vc(p5, 4.1381367970572387085E-8 ,bb4b,3431,2683,95f5, -24, .B1BB4B95F52683) 96 97 #ifdef vccast 98 #define ln2hi vccast(ln2hi) 99 #define ln2lo vccast(ln2lo) 100 #define lnhuge vccast(lnhuge) 101 #define lntiny vccast(lntiny) 102 #define invln2 vccast(invln2) 103 #define p1 vccast(p1) 104 #define p2 vccast(p2) 105 #define p3 vccast(p3) 106 #define p4 vccast(p4) 107 #define p5 vccast(p5) 108 #endif 109 110 ic(p1, 1.6666666666666601904E-1, -3, 1.555555555553E) 111 ic(p2, -2.7777777777015593384E-3, -9, -1.6C16C16BEBD93) 112 ic(p3, 6.6137563214379343612E-5, -14, 1.1566AAF25DE2C) 113 ic(p4, -1.6533902205465251539E-6, -20, -1.BBD41C5D26BF1) 114 ic(p5, 4.1381367970572384604E-8, -25, 1.6376972BEA4D0) 115 ic(ln2hi, 6.9314718036912381649E-1, -1, 1.62E42FEE00000) 116 ic(ln2lo, 1.9082149292705877000E-10,-33, 1.A39EF35793C76) 117 ic(lnhuge, 7.1602103751842355450E2, 9, 1.6602B15B7ECF2) 118 ic(lntiny,-7.5137154372698068983E2, 9, -1.77AF8EBEAE354) 119 ic(invln2, 1.4426950408889633870E0, 0, 1.71547652B82FE) 120 121 double 122 exp(double x) 123 { 124 double z,hi,lo,c; 125 int k; 126 127 #if !defined(__vax__)&&!defined(tahoe) 128 if(x!=x) return(x); /* x is NaN */ 129 #endif /* !defined(__vax__)&&!defined(tahoe) */ 130 if( x <= lnhuge ) { 131 if( x >= lntiny ) { 132 133 /* argument reduction : x --> x - k*ln2 */ 134 135 k=invln2*x+copysign(0.5,x); /* k=NINT(x/ln2) */ 136 137 /* express x-k*ln2 as hi-lo and let x=hi-lo rounded */ 138 139 hi=x-k*ln2hi; 140 x=hi-(lo=k*ln2lo); 141 142 /* return 2^k*[1+x+x*c/(2+c)] */ 143 z=x*x; 144 c= x - z*(p1+z*(p2+z*(p3+z*(p4+z*p5)))); 145 return scalb(1.0+(hi-(lo-(x*c)/(2.0-c))),k); 146 147 } 148 /* end of x > lntiny */ 149 150 else 151 /* exp(-big#) underflows to zero */ 152 if(finite(x)) return(scalb(1.0,-5000)); 153 154 /* exp(-INF) is zero */ 155 else return(0.0); 156 } 157 /* end of x < lnhuge */ 158 159 else 160 /* exp(INF) is INF, exp(+big#) overflows to INF */ 161 return( finite(x) ? scalb(1.0,5000) : x); 162 } 163 164 /* returns exp(r = x + c) for |c| < |x| with no overlap. */ 165 166 double 167 __exp__D(double x, double c) 168 { 169 double z,hi,lo; 170 int k; 171 172 #if !defined(__vax__)&&!defined(tahoe) 173 if (x!=x) return(x); /* x is NaN */ 174 #endif /* !defined(__vax__)&&!defined(tahoe) */ 175 if ( x <= lnhuge ) { 176 if ( x >= lntiny ) { 177 178 /* argument reduction : x --> x - k*ln2 */ 179 z = invln2*x; 180 k = z + copysign(.5, x); 181 182 /* express (x+c)-k*ln2 as hi-lo and let x=hi-lo rounded */ 183 184 hi=(x-k*ln2hi); /* Exact. */ 185 x= hi - (lo = k*ln2lo-c); 186 /* return 2^k*[1+x+x*c/(2+c)] */ 187 z=x*x; 188 c= x - z*(p1+z*(p2+z*(p3+z*(p4+z*p5)))); 189 c = (x*c)/(2.0-c); 190 191 return scalb(1.+(hi-(lo - c)), k); 192 } 193 /* end of x > lntiny */ 194 195 else 196 /* exp(-big#) underflows to zero */ 197 if(finite(x)) return(scalb(1.0,-5000)); 198 199 /* exp(-INF) is zero */ 200 else return(0.0); 201 } 202 /* end of x < lnhuge */ 203 204 else 205 /* exp(INF) is INF, exp(+big#) overflows to INF */ 206 return( finite(x) ? scalb(1.0,5000) : x); 207 } 208
Indexes created Thu Sep 25 16:09:42 GMT 2025