get_ui.c revision 1.1.1.3 
1/* mpfr_get_ui -- convert a floating-point number to an unsigned long.
2
3Copyright 2003-2004, 2006-2018 Free Software Foundation, Inc.
4Contributed by the AriC and Caramba projects, INRIA.
5
6This file is part of the GNU MPFR Library.
7
8The GNU MPFR Library is free software; you can redistribute it and/or modify
9it under the terms of the GNU Lesser General Public License as published by
10the Free Software Foundation; either version 3 of the License, or (at your
11option) any later version.
12
13The GNU MPFR Library is distributed in the hope that it will be useful, but
14WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
15or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
16License for more details.
17
18You should have received a copy of the GNU Lesser General Public License
19along with the GNU MPFR Library; see the file COPYING.LESSER.  If not, see
20http://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc.,
2151 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA. */
22
23#include "mpfr-impl.h"
24
25unsigned long
26mpfr_get_ui (mpfr_srcptr f, mpfr_rnd_t rnd)
27{
28  mpfr_prec_t prec;
29  unsigned long s;
30  mpfr_t x;
31  mp_size_t n;
32  mpfr_exp_t exp;
33  MPFR_SAVE_EXPO_DECL (expo);
34
35  if (MPFR_UNLIKELY (!mpfr_fits_ulong_p (f, rnd)))
36    {
37      MPFR_SET_ERANGEFLAG ();
38      return MPFR_IS_NAN (f) || MPFR_IS_NEG (f) ?
39        (unsigned long) 0 : ULONG_MAX;
40    }
41
42  if (MPFR_IS_ZERO (f))
43    return (unsigned long) 0;
44
45  for (s = ULONG_MAX, prec = 0; s != 0; s /= 2, prec ++)
46    { }
47
48  MPFR_SAVE_EXPO_MARK (expo);
49
50  /* first round to prec bits */
51  mpfr_init2 (x, prec);
52  mpfr_rint (x, f, rnd);
53
54  /* The flags from mpfr_rint are the wanted ones. In particular,
55     it sets the inexact flag when necessary. */
56  MPFR_SAVE_EXPO_UPDATE_FLAGS (expo, __gmpfr_flags);
57
58  /* warning: if x=0, taking its exponent is illegal */
59  if (MPFR_IS_ZERO(x))
60    s = 0;
61  else
62    {
63      /* now the result is in the most significant limb of x */
64      exp = MPFR_GET_EXP (x); /* since |x| >= 1, exp >= 1 */
65      n = MPFR_LIMB_SIZE(x);
66      s = MPFR_MANT(x)[n - 1] >> (GMP_NUMB_BITS - exp);
67    }
68
69  mpfr_clear (x);
70
71  MPFR_SAVE_EXPO_FREE (expo);
72
73  return s;
74}
75