/* $NetBSD: n_log10.c,v 1.1 1995/10/10 23:36:58 ragge Exp $ */ /* * 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[] = "@(#)log10.c 8.1 (Berkeley) 6/4/93"; #endif /* not lint */ /* LOG10(X) * RETURN THE BASE 10 LOGARITHM OF x * DOUBLE PRECISION (VAX D format 56 bits, IEEE DOUBLE 53 BITS) * CODED IN C BY K.C. NG, 1/20/85; * REVISED BY K.C. NG on 1/23/85, 3/7/85, 4/16/85. * * Required kernel function: * log(x) * * Method : * log(x) * log10(x) = --------- or [1/log(10)]*log(x) * log(10) * * Note: * [log(10)] rounded to 56 bits has error .0895 ulps, * [1/log(10)] rounded to 53 bits has error .198 ulps; * therefore, for better accuracy, in VAX D format, we divide * log(x) by log(10), but in IEEE Double format, we multiply * log(x) by [1/log(10)]. * * Special cases: * log10(x) is NaN with signal if x < 0; * log10(+INF) is +INF with no signal; log10(0) is -INF with signal; * log10(NaN) is that NaN with no signal. * * Accuracy: * log10(X) returns the exact log10(x) nearly rounded. In a test run * with 1,536,000 random arguments on a VAX, the maximum observed * error was 1.74 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(ln10hi, 2.3025850929940456790E0 ,5d8d,4113,a8ac,ddaa, 2, .935D8DDDAAA8AC) ic(ivln10, 4.3429448190325181667E-1, -2, 1.BCB7B1526E50E) #ifdef vccast #define ln10hi vccast(ln10hi) #endif double log10(x) double x; { #if defined(__vax__)||defined(tahoe) return(log(x)/ln10hi); #else /* defined(__vax__)||defined(tahoe) */ return(ivln10*log(x)); #endif /* defined(__vax__)||defined(tahoe) */ }