contrib/mpfr/fits_u.h

   1 /* mpfr_fits_*_p -- test whether an mpfr fits a C unsigned type.
   2
   3 Copyright 2003, 2004, 2005, 2006, 2007, 2008, 2009 Free Software Foundation, Inc.
   4 Contributed by the Arenaire and Cacao 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 2.1 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.LIB.  If not, write to
  20 the Free Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston,
  21 MA 02110-1301, USA. */
  22
  23 #include "mpfr-impl.h"
  24
  25 int
  26 FUNCTION (mpfr_srcptr f, mp_rnd_t rnd)
  27 {
  28   mp_exp_t exp;
  29   mp_prec_t prec;
  30   TYPE s;
  31   mpfr_t x;
  32   int res;
  33
  34   if (MPFR_UNLIKELY (MPFR_IS_SINGULAR (f)))
  35     /* Zero always fit */
  36     return MPFR_IS_ZERO (f) ? 1 : 0;
  37   else if (MPFR_IS_NEG (f))
  38     /* Negative numbers doesn't fit */
  39     return 0;
  40   /* now it fits if
  41      (a) f <= MAXIMUM
  42      (b) round(f, prec(slong), rnd) <= MAXIMUM */
  43
  44   exp = MPFR_GET_EXP (f);
  45   if (exp < 1)
  46     return 1; /* |f| < 1: always fits */
  47
  48   /* first compute prec(MAXIMUM) */
  49   for (s = MAXIMUM, prec = 0; s != 0; s /= 2, prec ++);
  50
  51   /* MAXIMUM needs prec bits, i.e. 2^(prec-1) <= |MAXIMUM| < 2^prec */
  52
  53    /* if exp < prec - 1, then f < 2^(prec-1) < |MAXIMUM| */
  54   if ((mpfr_prec_t) exp < prec - 1)
  55     return 1;
  56
  57   /* if exp > prec + 1, then f >= 2^prec > MAXIMUM */
  58   if ((mpfr_prec_t) exp > prec + 1)
  59     return 0;
  60
  61   /* remains cases exp = prec-1 to prec+1 */
  62
  63   /* hard case: first round to prec bits, then check */
  64   mpfr_init2 (x, prec);
  65   mpfr_set (x, f, rnd);
  66   res = mpfr_cmp_ui (x, MAXIMUM) <= 0;
  67   mpfr_clear (x);
  68
  69   return res;
  70 }
  71