sysdeps/generic/frexp.c

   1 /* Copyright (C) 1991, 1992 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 /* Break VALUE into a normalized fraction and an integral power of 2.  */
  24 double
  25 DEFUN(frexp, (value, exp), double value AND int *exp)
  26 {
  27 #ifdef  NAN
  28   if (__isinf (value))
  29     {
  30       errno = EDOM;
  31       *exp = 0;
  32       return __copysign (NAN, value);
  33     }
  34 #endif
  35
  36   if (__isnan (value))
  37     {
  38       errno = EDOM;
  39       *exp = 0;
  40       return value;
  41     }
  42
  43   if (value == 0)
  44     {
  45       *exp = 0;
  46       return value;
  47     }
  48
  49   /* Add one to the exponent of the number,
  50      so we have one digit before the binary point.  */
  51   *exp = (int) __logb (value) + 1;
  52   return ldexp (value, - *exp);
  53 }