lib/ilogb.c

   1 /* Floating-point exponent.
   2    Copyright (C) 2012-2024 Free Software Foundation, Inc.
   3
   4    This file is free software: you can redistribute it and/or modify
   5    it under the terms of the GNU Lesser General Public License as
   6    published by the Free Software Foundation, either version 3 of the
   7    License, or (at your option) any later version.
   8
   9    This file 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
  12    GNU Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public License
  15    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  16
  17 #if ! (defined USE_LONG_DOUBLE || defined USE_FLOAT)
  18 # include <config.h>
  19 #endif
  20
  21 /* Specification.  */
  22 #include <math.h>
  23
  24 #include <limits.h>
  25
  26 #ifdef USE_LONG_DOUBLE
  27 # define ILOGB ilogbl
  28 # define DOUBLE long double
  29 # define L_(literal) literal##L
  30 # define FREXP frexpl
  31 # define ISNAN isnanl
  32 #elif ! defined USE_FLOAT
  33 # define ILOGB ilogb
  34 # define DOUBLE double
  35 # define L_(literal) literal
  36 # define FREXP frexp
  37 # define ISNAN isnand
  38 #else /* defined USE_FLOAT */
  39 # define ILOGB ilogbf
  40 # define DOUBLE float
  41 # define L_(literal) literal##f
  42 # define FREXP frexpf
  43 # define ISNAN isnanf
  44 #endif
  45
  46 int
  47 ILOGB (DOUBLE x)
  48 {
  49   if (isfinite (x))
  50     {
  51       if (x == L_(0.0))
  52         return FP_ILOGB0;
  53       else
  54         {
  55           int e;
  56
  57           (void) FREXP (x, &e);
  58           return e - 1;
  59         }
  60     }
  61   else
  62     {
  63       if (ISNAN (x))
  64         return FP_ILOGBNAN;
  65       else
  66         return INT_MAX;
  67     }
  68 }