1 /* $NetBSD: n_log10.c,v 1.6 2003/08/07 16:44:52 agc 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. Neither the name of the University nor the names of its contributors 15 * may be used to endorse or promote products derived from this software 16 * without specific prior written permission. 17 * 18 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 19 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 20 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 21 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 22 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 23 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 24 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 25 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 26 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 27 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 28 * SUCH DAMAGE. 29 */ 30 31 #ifndef lint 32 #if 0 33 static char sccsid[] = "@(#)log10.c 8.1 (Berkeley) 6/4/93"; 34 #endif 35 #endif /* not lint */ 36 37 /* LOG10(X) 38 * RETURN THE BASE 10 LOGARITHM OF x 39 * DOUBLE PRECISION (VAX D format 56 bits, IEEE DOUBLE 53 BITS) 40 * CODED IN C BY K.C. NG, 1/20/85; 41 * REVISED BY K.C. NG on 1/23/85, 3/7/85, 4/16/85. 42 * 43 * Required kernel function: 44 * log(x) 45 * 46 * Method : 47 * log(x) 48 * log10(x) = --------- or [1/log(10)]*log(x) 49 * log(10) 50 * 51 * Note: 52 * [log(10)] rounded to 56 bits has error .0895 ulps, 53 * [1/log(10)] rounded to 53 bits has error .198 ulps; 54 * therefore, for better accuracy, in VAX D format, we divide 55 * log(x) by log(10), but in IEEE Double format, we multiply 56 * log(x) by [1/log(10)]. 57 * 58 * Special cases: 59 * log10(x) is NaN with signal if x < 0; 60 * log10(+INF) is +INF with no signal; log10(0) is -INF with signal; 61 * log10(NaN) is that NaN with no signal. 62 * 63 * Accuracy: 64 * log10(X) returns the exact log10(x) nearly rounded. In a test run 65 * with 1,536,000 random arguments on a VAX, the maximum observed 66 * error was 1.74 ulps (units in the last place). 67 * 68 * Constants: 69 * The hexadecimal values are the intended ones for the following constants. 70 * The decimal values may be used, provided that the compiler will convert 71 * from decimal to binary accurately enough to produce the hexadecimal values 72 * shown. 73 */ 74 75 #define _LIBM_STATIC 76 #include "mathimpl.h" 77 78 vc(ln10hi, 2.3025850929940456790E0 ,5d8d,4113,a8ac,ddaa, 2, .935D8DDDAAA8AC) 79 80 ic(ivln10, 4.3429448190325181667E-1, -2, 1.BCB7B1526E50E) 81 82 #ifdef vccast 83 #define ln10hi vccast(ln10hi) 84 #endif 85 86 87 double 88 log10(double x) 89 { 90 #if defined(__vax__)||defined(tahoe) 91 return(log(x)/ln10hi); 92 #else /* defined(__vax__)||defined(tahoe) */ 93 return(ivln10*log(x)); 94 #endif /* defined(__vax__)||defined(tahoe) */ 95 } 96