div_2ui.c revision 1.1.1.1 
1/* mpfr_div_2ui -- divide a floating-point number by a power of two
2
3Copyright 1999, 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#include "mpfr-impl.h"
24
25int
26mpfr_div_2ui (mpfr_ptr y, mpfr_srcptr x, unsigned long n, mpfr_rnd_t rnd_mode)
27{
28  int inexact;
29
30  MPFR_LOG_FUNC (("x[%#R]=%R n=%lu rnd=%d", x, x, n, rnd_mode),
31                 ("y[%#R]=%R inexact=%d", y, y, inexact));
32
33  if (MPFR_UNLIKELY (MPFR_IS_SINGULAR (x)))
34    return mpfr_set (y, x, rnd_mode);
35  else
36    {
37      mpfr_exp_t exp = MPFR_GET_EXP (x);
38      mpfr_uexp_t diffexp;
39
40      MPFR_SETRAW (inexact, y, x, exp, rnd_mode);
41      diffexp = (mpfr_uexp_t) exp - (mpfr_uexp_t) (__gmpfr_emin - 1);
42      if (MPFR_UNLIKELY (n >= diffexp))  /* exp - n <= emin - 1 */
43        {
44          if (rnd_mode == MPFR_RNDN &&
45              (n > diffexp || (inexact >= 0 && mpfr_powerof2_raw (y))))
46            rnd_mode = MPFR_RNDZ;
47          return mpfr_underflow (y, rnd_mode, MPFR_SIGN (y));
48        }
49      /* exp - n >= emin (no underflow, no integer overflow) */
50      while (n > LONG_MAX)
51        {
52          n -= LONG_MAX;
53          exp -= LONG_MAX;  /* note: signed values */
54        }
55      MPFR_SET_EXP (y, exp - (long) n);
56    }
57
58  MPFR_RET (inexact);
59}
60