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n_log10.c revision 1.6.54.1
      1  1.6.54.1    yamt /*      $NetBSD: n_log10.c,v 1.6.54.1 2014/05/22 11:36:57 yamt Exp $ */
      2       1.1   ragge /*
      3       1.1   ragge  * Copyright (c) 1985, 1993
      4       1.1   ragge  *	The Regents of the University of California.  All rights reserved.
      5       1.1   ragge  *
      6       1.1   ragge  * Redistribution and use in source and binary forms, with or without
      7       1.1   ragge  * modification, are permitted provided that the following conditions
      8       1.1   ragge  * are met:
      9       1.1   ragge  * 1. Redistributions of source code must retain the above copyright
     10       1.1   ragge  *    notice, this list of conditions and the following disclaimer.
     11       1.1   ragge  * 2. Redistributions in binary form must reproduce the above copyright
     12       1.1   ragge  *    notice, this list of conditions and the following disclaimer in the
     13       1.1   ragge  *    documentation and/or other materials provided with the distribution.
     14       1.6     agc  * 3. Neither the name of the University nor the names of its contributors
     15       1.1   ragge  *    may be used to endorse or promote products derived from this software
     16       1.1   ragge  *    without specific prior written permission.
     17       1.1   ragge  *
     18       1.1   ragge  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     19       1.1   ragge  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     20       1.1   ragge  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     21       1.1   ragge  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     22       1.1   ragge  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     23       1.1   ragge  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     24       1.1   ragge  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     25       1.1   ragge  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     26       1.1   ragge  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     27       1.1   ragge  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     28       1.1   ragge  * SUCH DAMAGE.
     29       1.1   ragge  */
     30       1.1   ragge 
     31       1.1   ragge #ifndef lint
     32       1.2   ragge #if 0
     33       1.1   ragge static char sccsid[] = "@(#)log10.c	8.1 (Berkeley) 6/4/93";
     34       1.2   ragge #endif
     35       1.1   ragge #endif /* not lint */
     36       1.1   ragge 
     37       1.1   ragge /* LOG10(X)
     38       1.1   ragge  * RETURN THE BASE 10 LOGARITHM OF x
     39       1.1   ragge  * DOUBLE PRECISION (VAX D format 56 bits, IEEE DOUBLE 53 BITS)
     40       1.4  simonb  * CODED IN C BY K.C. NG, 1/20/85;
     41       1.1   ragge  * REVISED BY K.C. NG on 1/23/85, 3/7/85, 4/16/85.
     42       1.4  simonb  *
     43       1.1   ragge  * Required kernel function:
     44       1.1   ragge  *	log(x)
     45       1.1   ragge  *
     46       1.1   ragge  * Method :
     47       1.1   ragge  *			     log(x)
     48       1.1   ragge  *		log10(x) = ---------  or  [1/log(10)]*log(x)
     49       1.1   ragge  *			    log(10)
     50       1.1   ragge  *
     51       1.1   ragge  *    Note:
     52       1.1   ragge  *	  [log(10)]   rounded to 56 bits has error  .0895  ulps,
     53       1.1   ragge  *	  [1/log(10)] rounded to 53 bits has error  .198   ulps;
     54       1.4  simonb  *	  therefore, for better accuracy, in VAX D format, we divide
     55       1.4  simonb  *	  log(x) by log(10), but in IEEE Double format, we multiply
     56       1.1   ragge  *	  log(x) by [1/log(10)].
     57       1.1   ragge  *
     58       1.1   ragge  * Special cases:
     59       1.4  simonb  *	log10(x) is NaN with signal if x < 0;
     60       1.1   ragge  *	log10(+INF) is +INF with no signal; log10(0) is -INF with signal;
     61       1.1   ragge  *	log10(NaN) is that NaN with no signal.
     62       1.1   ragge  *
     63       1.1   ragge  * Accuracy:
     64       1.1   ragge  *	log10(X) returns the exact log10(x) nearly rounded. In a test run
     65       1.1   ragge  *	with 1,536,000 random arguments on a VAX, the maximum observed
     66       1.1   ragge  *	error was 1.74 ulps (units in the last place).
     67       1.1   ragge  *
     68       1.1   ragge  * Constants:
     69       1.1   ragge  * The hexadecimal values are the intended ones for the following constants.
     70       1.1   ragge  * The decimal values may be used, provided that the compiler will convert
     71       1.1   ragge  * from decimal to binary accurately enough to produce the hexadecimal values
     72       1.1   ragge  * shown.
     73       1.1   ragge  */
     74       1.1   ragge 
     75       1.5    matt #define _LIBM_STATIC
     76       1.1   ragge #include "mathimpl.h"
     77       1.1   ragge 
     78       1.1   ragge vc(ln10hi, 2.3025850929940456790E0 ,5d8d,4113,a8ac,ddaa, 2, .935D8DDDAAA8AC)
     79       1.1   ragge 
     80       1.1   ragge ic(ivln10, 4.3429448190325181667E-1, -2, 1.BCB7B1526E50E)
     81       1.1   ragge 
     82       1.1   ragge #ifdef vccast
     83       1.1   ragge #define	ln10hi	vccast(ln10hi)
     84       1.1   ragge #endif
     85       1.1   ragge 
     86       1.1   ragge 
     87       1.5    matt double
     88       1.5    matt log10(double x)
     89       1.1   ragge {
     90       1.3    matt #if defined(__vax__)||defined(tahoe)
     91       1.1   ragge 	return(log(x)/ln10hi);
     92       1.3    matt #else	/* defined(__vax__)||defined(tahoe) */
     93       1.1   ragge 	return(ivln10*log(x));
     94       1.3    matt #endif	/* defined(__vax__)||defined(tahoe) */
     95       1.1   ragge }
     96  1.6.54.1    yamt 
     97  1.6.54.1    yamt float
     98  1.6.54.1    yamt log10f(float x)
     99  1.6.54.1    yamt {
    100  1.6.54.1    yamt #if defined(__vax__)||defined(tahoe)
    101  1.6.54.1    yamt 	return(logf(x)/ln10hi);
    102  1.6.54.1    yamt #else	/* defined(__vax__)||defined(tahoe) */
    103  1.6.54.1    yamt 	return(ivln10*log(x));
    104  1.6.54.1    yamt #endif	/* defined(__vax__)||defined(tahoe) */
    105  1.6.54.1    yamt }
    106