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      1 /*      $NetBSD: n_log10.c,v 1.8 2024/07/16 14:52:50 riastradh 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 #include <sys/cdefs.h>
     32 __RCSID("$NetBSD: n_log10.c,v 1.8 2024/07/16 14:52:50 riastradh Exp $");
     33 
     34 #ifndef lint
     35 #if 0
     36 static char sccsid[] = "@(#)log10.c	8.1 (Berkeley) 6/4/93";
     37 #endif
     38 #endif /* not lint */
     39 
     40 /* LOG10(X)
     41  * RETURN THE BASE 10 LOGARITHM OF x
     42  * DOUBLE PRECISION (VAX D format 56 bits, IEEE DOUBLE 53 BITS)
     43  * CODED IN C BY K.C. NG, 1/20/85;
     44  * REVISED BY K.C. NG on 1/23/85, 3/7/85, 4/16/85.
     45  *
     46  * Required kernel function:
     47  *	log(x)
     48  *
     49  * Method :
     50  *			     log(x)
     51  *		log10(x) = ---------  or  [1/log(10)]*log(x)
     52  *			    log(10)
     53  *
     54  *    Note:
     55  *	  [log(10)]   rounded to 56 bits has error  .0895  ulps,
     56  *	  [1/log(10)] rounded to 53 bits has error  .198   ulps;
     57  *	  therefore, for better accuracy, in VAX D format, we divide
     58  *	  log(x) by log(10), but in IEEE Double format, we multiply
     59  *	  log(x) by [1/log(10)].
     60  *
     61  * Special cases:
     62  *	log10(x) is NaN with signal if x < 0;
     63  *	log10(+INF) is +INF with no signal; log10(0) is -INF with signal;
     64  *	log10(NaN) is that NaN with no signal.
     65  *
     66  * Accuracy:
     67  *	log10(X) returns the exact log10(x) nearly rounded. In a test run
     68  *	with 1,536,000 random arguments on a VAX, the maximum observed
     69  *	error was 1.74 ulps (units in the last place).
     70  *
     71  * Constants:
     72  * The hexadecimal values are the intended ones for the following constants.
     73  * The decimal values may be used, provided that the compiler will convert
     74  * from decimal to binary accurately enough to produce the hexadecimal values
     75  * shown.
     76  */
     77 
     78 #include "namespace.h"
     79 
     80 #define _LIBM_STATIC
     81 #include "mathimpl.h"
     82 
     83 vc(ln10hi, 2.3025850929940456790E0 ,5d8d,4113,a8ac,ddaa, 2, .935D8DDDAAA8AC)
     84 
     85 ic(ivln10, 4.3429448190325181667E-1, -2, 1.BCB7B1526E50E)
     86 
     87 #ifdef vccast
     88 #define	ln10hi	vccast(ln10hi)
     89 #endif
     90 
     91 __weak_alias(log10l, _log10l)
     92 __strong_alias(_log10l, _log10)
     93 
     94 __weak_alias(log10, _log10)
     95 double
     96 log10(double x)
     97 {
     98 #if defined(__vax__)||defined(tahoe)
     99 	return(log(x)/ln10hi);
    100 #else	/* defined(__vax__)||defined(tahoe) */
    101 	return(ivln10*log(x));
    102 #endif	/* defined(__vax__)||defined(tahoe) */
    103 }
    104 
    105 __weak_alias(log10f, _log10f)
    106 float
    107 log10f(float x)
    108 {
    109 #if defined(__vax__)||defined(tahoe)
    110 	return(logf(x)/ln10hi);
    111 #else	/* defined(__vax__)||defined(tahoe) */
    112 	return(ivln10*log(x));
    113 #endif	/* defined(__vax__)||defined(tahoe) */
    114 }
    115