1/* mpfr_sub_ui -- subtract a floating-point number and a machine integer
2
3Copyright 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013 Free Software Foundation, Inc.
4Contributed by the AriC and Caramel 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
24#define MPFR_NEED_LONGLONG_H
25#include "mpfr-impl.h"
26
27int
28mpfr_sub_ui (mpfr_ptr y, mpfr_srcptr x, unsigned long int u, mpfr_rnd_t rnd_mode)
29{
30  if (MPFR_LIKELY (u != 0))  /* if u=0, do nothing */
31    {
32      mpfr_t uu;
33      mp_limb_t up[1];
34      unsigned long cnt;
35      int inex;
36
37      MPFR_SAVE_EXPO_DECL (expo);
38
39      MPFR_LOG_FUNC
40        (("x[%Pu]=%.*Rg u=%lu rnd=%d",
41          mpfr_get_prec(x), mpfr_log_prec, x, u, rnd_mode),
42         ("y[%Pu]=%.*Rg inexact=%d",
43          mpfr_get_prec(y), mpfr_log_prec, y, inex));
44
45      MPFR_TMP_INIT1 (up, uu, GMP_NUMB_BITS);
46      MPFR_ASSERTN (u == (mp_limb_t) u);
47      count_leading_zeros (cnt, (mp_limb_t) u);
48      *up = (mp_limb_t) u << cnt;
49
50      /* Optimization note: Exponent save/restore operations may be
51         removed if mpfr_sub works even when uu is out-of-range. */
52      MPFR_SAVE_EXPO_MARK (expo);
53      MPFR_SET_EXP (uu, GMP_NUMB_BITS - cnt);
54      inex = mpfr_sub (y, x, uu, rnd_mode);
55      MPFR_SAVE_EXPO_FREE (expo);
56      return mpfr_check_range (y, inex, rnd_mode);
57    }
58  else
59    return mpfr_set (y, x, rnd_mode);
60}
61