lib/libm/noieee_src/n_log10.c

   1 /*      $NetBSD: n_log10.c,v 1.5 2002/06/15 00:10:17 matt 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 }