sysdeps/generic/log10.c

   1 /* Copyright (C) 1991 Free Software Foundation, Inc.
   2 This file is part of the GNU C Library.
   3
   4 The GNU C Library is free software; you can redistribute it and/or
   5 modify it under the terms of the GNU Library General Public License as
   6 published by the Free Software Foundation; either version 2 of the
   7 License, or (at your option) any later version.
   8
   9 The GNU C Library is distributed in the hope that it will be useful,
  10 but WITHOUT ANY WARRANTY; without even the implied warranty of
  11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12 Library General Public License for more details.
  13
  14 You should have received a copy of the GNU Library General Public
  15 License along with the GNU C Library; see the file COPYING.LIB.  If
  16 not, write to the Free Software Foundation, Inc., 675 Mass Ave,
  17 Cambridge, MA 02139, USA.  */
  18
  19 #include <ansidecl.h>
  20 #include <errno.h>
  21 #include <math.h>
  22
  23 #ifndef LN10
  24 #define LN10    log(10.0)
  25 #endif
  26
  27 /* Return the base-ten logarithm of X.  */
  28 double
  29 DEFUN(log10, (x), double x)
  30 {
  31   static double ln10 = 0.0;
  32
  33   if (ln10 == 0.0)
  34     ln10 = LN10;
  35
  36   return log(x) / ln10;
  37 }