1 /* $NetBSD: n_log10.c,v 1.5 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[] = "@(#)log10.c 8.1 (Berkeley) 6/4/93"; 38 #endif 39 #endif /* not lint */ 40 41 /* LOG10(X) 42 * RETURN THE BASE 10 LOGARITHM OF x 43 * DOUBLE PRECISION (VAX D format 56 bits, IEEE DOUBLE 53 BITS) 44 * CODED IN C BY K.C. NG, 1/20/85; 45 * REVISED BY K.C. NG on 1/23/85, 3/7/85, 4/16/85. 46 * 47 * Required kernel function: 48 * log(x) 49 * 50 * Method : 51 * log(x) 52 * log10(x) = --------- or [1/log(10)]*log(x) 53 * log(10) 54 * 55 * Note: 56 * [log(10)] rounded to 56 bits has error .0895 ulps, 57 * [1/log(10)] rounded to 53 bits has error .198 ulps; 58 * therefore, for better accuracy, in VAX D format, we divide 59 * log(x) by log(10), but in IEEE Double format, we multiply 60 * log(x) by [1/log(10)]. 61 * 62 * Special cases: 63 * log10(x) is NaN with signal if x < 0; 64 * log10(+INF) is +INF with no signal; log10(0) is -INF with signal; 65 * log10(NaN) is that NaN with no signal. 66 * 67 * Accuracy: 68 * log10(X) returns the exact log10(x) nearly rounded. In a test run 69 * with 1,536,000 random arguments on a VAX, the maximum observed 70 * error was 1.74 ulps (units in the last place). 71 * 72 * Constants: 73 * The hexadecimal values are the intended ones for the following constants. 74 * The decimal values may be used, provided that the compiler will convert 75 * from decimal to binary accurately enough to produce the hexadecimal values 76 * shown. 77 */ 78 79 #define _LIBM_STATIC 80 #include "mathimpl.h" 81 82 vc(ln10hi, 2.3025850929940456790E0 ,5d8d,4113,a8ac,ddaa, 2, .935D8DDDAAA8AC) 83 84 ic(ivln10, 4.3429448190325181667E-1, -2, 1.BCB7B1526E50E) 85 86 #ifdef vccast 87 #define ln10hi vccast(ln10hi) 88 #endif 89 90 91 double 92 log10(double x) 93 { 94 #if defined(__vax__)||defined(tahoe) 95 return(log(x)/ln10hi); 96 #else /* defined(__vax__)||defined(tahoe) */ 97 return(ivln10*log(x)); 98 #endif /* defined(__vax__)||defined(tahoe) */ 99 } 100