lib/logb.c

   1 /* Floating-point exponent.
   2    Copyright (C) 2012-2021 Free Software Foundation, Inc.
   3
   4    This program is free software: you can redistribute it and/or modify
   5    it under the terms of the GNU General Public License as published by
   6    the Free Software Foundation; either version 3 of the License, or
   7    (at your option) any later version.
   8
   9    This program 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 General Public License for more details.
  13
  14    You should have received a copy of the GNU 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 #ifdef USE_LONG_DOUBLE
  25 # define LOGB logbl
  26 # define DOUBLE long double
  27 # define L_(literal) literal##L
  28 # define HUGEVAL HUGE_VALL
  29 # define FREXP frexpl
  30 # define ISNAN isnanl
  31 #elif ! defined USE_FLOAT
  32 # define LOGB logb
  33 # define DOUBLE double
  34 # define L_(literal) literal
  35 # define HUGEVAL HUGE_VAL
  36 # define FREXP frexp
  37 # define ISNAN isnand
  38 #else /* defined USE_FLOAT */
  39 # define LOGB logbf
  40 # define DOUBLE float
  41 # define L_(literal) literal##f
  42 # define HUGEVAL HUGE_VALF
  43 # define FREXP frexpf
  44 # define ISNAN isnanf
  45 #endif
  46
  47 DOUBLE
  48 LOGB (DOUBLE x)
  49 {
  50   if (isfinite (x))
  51     {
  52       if (x == L_(0.0))
  53         /* Return -Infinity.  */
  54         return - HUGEVAL;
  55       else
  56         {
  57           int e;
  58
  59           (void) FREXP (x, &e);
  60           return (DOUBLE) (e - 1);
  61         }
  62     }
  63   else
  64     {
  65       if (ISNAN (x))
  66         return x; /* NaN */
  67       else
  68         /* Return +Infinity.  */
  69         return HUGEVAL;
  70     }
  71 }