mul_2ui.c revision 1.1.1.1 
1/* mpfr_mul_2ui -- multiply 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_mul_2ui (mpfr_ptr y, mpfr_srcptr x, unsigned long int 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  inexact = MPFR_UNLIKELY(y != x) ? mpfr_set (y, x, rnd_mode) : 0;
34
35  if (MPFR_LIKELY( MPFR_IS_PURE_FP(y)) )
36    {
37      /* n will have to be casted to long to make sure that the addition
38         and subtraction below (for overflow detection) are signed */
39      while (MPFR_UNLIKELY(n > LONG_MAX))
40        {
41          int inex2;
42
43          n -= LONG_MAX;
44          inex2 = mpfr_mul_2ui(y, y, LONG_MAX, rnd_mode);
45          if (inex2)
46            return inex2; /* overflow */
47        }
48
49      /* MPFR_EMIN_MIN + (long) n is signed and doesn't lead to an overflow;
50         the first test useful so that the real test can't lead to an
51         overflow. */
52      {
53        mpfr_exp_t exp = MPFR_GET_EXP (y);
54        if (MPFR_UNLIKELY( __gmpfr_emax < MPFR_EMIN_MIN + (long) n ||
55                           exp > __gmpfr_emax - (long) n))
56          return mpfr_overflow (y, rnd_mode, MPFR_SIGN(y));
57
58        MPFR_SET_EXP (y, exp + (long) n);
59      }
60    }
61
62  return inexact;
63}
64