1/* mpfr_ui_sub -- subtract a floating-point number from an integer
2
3Copyright 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 Free Software Foundation, Inc.
4Contributed by the Arenaire and Cacao 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#define MPFR_NEED_LONGLONG_H
24#include "mpfr-impl.h"
25
26int
27mpfr_ui_sub (mpfr_ptr y, unsigned long int u, mpfr_srcptr x, mpfr_rnd_t rnd_mode)
28{
29  mpfr_t uu;
30  mp_limb_t up[1];
31  unsigned long cnt;
32
33  if (MPFR_UNLIKELY (u == 0))
34    return mpfr_neg (y, x, rnd_mode);
35
36  if (MPFR_UNLIKELY(MPFR_IS_SINGULAR(x)))
37    {
38      if (MPFR_IS_NAN(x))
39        {
40          MPFR_SET_NAN(y);
41          MPFR_RET_NAN;
42        }
43      else if (MPFR_IS_INF(x))
44        {
45          /*  u - Inf = -Inf and u - -Inf = +Inf  */
46          MPFR_SET_INF(y);
47          MPFR_SET_OPPOSITE_SIGN(y,x);
48          MPFR_RET(0); /* +/-infinity is exact */
49        }
50      else /* x is zero */
51        /* u - 0 = u */
52        return mpfr_set_ui(y, u, rnd_mode);
53    }
54  else
55    {
56      MPFR_TMP_INIT1 (up, uu, GMP_NUMB_BITS);
57      MPFR_ASSERTN(u == (mp_limb_t) u);
58      count_leading_zeros (cnt, (mp_limb_t) u);
59      *up = (mp_limb_t) u << cnt;
60      MPFR_SET_EXP (uu, GMP_NUMB_BITS - cnt);
61      return mpfr_sub (y, uu, x, rnd_mode);
62    }
63}
64