contrib/mpfr/mul_2ui.c

   1 /* mpfr_mul_2ui -- multiply a floating-point number by a power of two
   2
   3 Copyright 1999, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009 Free Software Foundation, Inc.
   4 Contributed by the Arenaire and Cacao projects, INRIA.
   5
   6 This file is part of the GNU MPFR Library.
   7
   8 The GNU MPFR Library is free software; you can redistribute it and/or modify
   9 it under the terms of the GNU Lesser General Public License as published by
  10 the Free Software Foundation; either version 2.1 of the License, or (at your
  11 option) any later version.
  12
  13 The GNU MPFR Library is distributed in the hope that it will be useful, but
  14 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
  15 or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
  16 License for more details.
  17
  18 You should have received a copy of the GNU Lesser General Public License
  19 along with the GNU MPFR Library; see the file COPYING.LIB.  If not, write to
  20 the Free Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston,
  21 MA 02110-1301, USA. */
  22
  23 #include "mpfr-impl.h"
  24
  25 int
  26 mpfr_mul_2ui (mpfr_ptr y, mpfr_srcptr x, unsigned long int n, mp_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         mp_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 }