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n_log10.c revision 1.1 
      1 /*      $NetBSD: n_log10.c,v 1.1 1995/10/10 23:36:58 ragge 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 static char sccsid[] = "@(#)log10.c	8.1 (Berkeley) 6/4/93";
     37 #endif /* not lint */
     38 
     39 /* LOG10(X)
     40  * RETURN THE BASE 10 LOGARITHM OF x
     41  * DOUBLE PRECISION (VAX D format 56 bits, IEEE DOUBLE 53 BITS)
     42  * CODED IN C BY K.C. NG, 1/20/85;
     43  * REVISED BY K.C. NG on 1/23/85, 3/7/85, 4/16/85.
     44  *
     45  * Required kernel function:
     46  *	log(x)
     47  *
     48  * Method :
     49  *			     log(x)
     50  *		log10(x) = ---------  or  [1/log(10)]*log(x)
     51  *			    log(10)
     52  *
     53  *    Note:
     54  *	  [log(10)]   rounded to 56 bits has error  .0895  ulps,
     55  *	  [1/log(10)] rounded to 53 bits has error  .198   ulps;
     56  *	  therefore, for better accuracy, in VAX D format, we divide
     57  *	  log(x) by log(10), but in IEEE Double format, we multiply
     58  *	  log(x) by [1/log(10)].
     59  *
     60  * Special cases:
     61  *	log10(x) is NaN with signal if x < 0;
     62  *	log10(+INF) is +INF with no signal; log10(0) is -INF with signal;
     63  *	log10(NaN) is that NaN with no signal.
     64  *
     65  * Accuracy:
     66  *	log10(X) returns the exact log10(x) nearly rounded. In a test run
     67  *	with 1,536,000 random arguments on a VAX, the maximum observed
     68  *	error was 1.74 ulps (units in the last place).
     69  *
     70  * Constants:
     71  * The hexadecimal values are the intended ones for the following constants.
     72  * The decimal values may be used, provided that the compiler will convert
     73  * from decimal to binary accurately enough to produce the hexadecimal values
     74  * shown.
     75  */
     76 
     77 #include "mathimpl.h"
     78 
     79 vc(ln10hi, 2.3025850929940456790E0 ,5d8d,4113,a8ac,ddaa, 2, .935D8DDDAAA8AC)
     80 
     81 ic(ivln10, 4.3429448190325181667E-1, -2, 1.BCB7B1526E50E)
     82 
     83 #ifdef vccast
     84 #define	ln10hi	vccast(ln10hi)
     85 #endif
     86 
     87 
     88 double log10(x)
     89 double x;
     90 {
     91 #if defined(vax)||defined(tahoe)
     92 	return(log(x)/ln10hi);
     93 #else	/* defined(vax)||defined(tahoe) */
     94 	return(ivln10*log(x));
     95 #endif	/* defined(vax)||defined(tahoe) */
     96 }
     97