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n_log10.c revision 1.6 
      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