source/libs/mpfr/mpfr-3.1.3/src/uceil_exp2.c

   1 /* __gmpfr_ceil_exp2 - returns y >= 2^d
   2
   3 Copyright 1999-2004, 2006-2015 Free Software Foundation, Inc.
   4 Contributed by the AriC and Caramel projects, INRIA.
   5
   6 This file is part of the GNU MPFR Library.
   7
   8 The GNU MPFR Library is free software; you can redistribute it and/or modify
   9 it under the terms of the GNU Lesser General Public License as published by
  10 the Free Software Foundation; either version 3 of the License, or (at your
  11 option) any later version.
  12
  13 The GNU MPFR Library is distributed in the hope that it will be useful, but
  14 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
  15 or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
  16 License for more details.
  17
  18 You should have received a copy of the GNU Lesser General Public License
  19 along with the GNU MPFR Library; see the file COPYING.LESSER.  If not, see
  20 http://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc.,
  21 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA. */
  22
  23 #include "mpfr-impl.h"
  24
  25 /* returns y >= 2^d, assuming that d <= 1024
  26    for d integer, returns exactly 2^d
  27 */
  28 double
  29 __gmpfr_ceil_exp2 (double d)
  30 {
  31   long exp;
  32 #if _GMP_IEEE_FLOATS
  33   union ieee_double_extract x;
  34 #else
  35   struct {double d;} x;
  36 #endif
  37
  38   MPFR_ASSERTN(d <= 1024.0);
  39   exp = (long) d;
  40   if (d != (double) exp)
  41     exp++;
  42   /* now exp = ceil(d) */
  43   x.d = 1.0;
  44 #if _GMP_IEEE_FLOATS
  45   x.s.exp = exp <= -1022 ? 1 : 1023 + exp;
  46 #else
  47   if (exp >= 0)
  48     {
  49       while (exp != 0)
  50         {
  51           x.d *= 2.0;
  52           exp--;
  53         }
  54     }
  55   else
  56     {
  57       while (exp != 0)
  58         {
  59           x.d *= (1.0 / 2.0);
  60           exp++;
  61         }
  62     }
  63 #endif
  64   return x.d;
  65 }