xref: /dflybsd-src/contrib/mpfr/src/mul_2ui.c (revision 2786097444a0124b5d33763854de247e230c6629)

/* mpfr_mul_2ui -- multiply a floating-point number by a power of two

Copyright 1999, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013 Free Software Foundation, Inc.
Contributed by the AriC and Caramel projects, INRIA.

This file is part of the GNU MPFR Library.

The GNU MPFR Library is free software; you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 3 of the License, or (at your
option) any later version.

The GNU MPFR Library is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
License for more details.

You should have received a copy of the GNU Lesser General Public License
along with the GNU MPFR Library; see the file COPYING.LESSER.  If not, see
http://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc.,
51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA. */

#include "mpfr-impl.h"

int
mpfr_mul_2ui (mpfr_ptr y, mpfr_srcptr x, unsigned long int n, mpfr_rnd_t rnd_mode)
{
  int inexact;

  MPFR_LOG_FUNC
    (("x[%Pu]=%.*Rg n=%lu rnd=%d",
      mpfr_get_prec (x), mpfr_log_prec, x, n, rnd_mode),
     ("y[%Pu]=%.*Rg inexact=%d",
      mpfr_get_prec (y), mpfr_log_prec, y, inexact));

  inexact = MPFR_UNLIKELY(y != x) ? mpfr_set (y, x, rnd_mode) : 0;

  if (MPFR_LIKELY( MPFR_IS_PURE_FP(y)) )
    {
      /* n will have to be casted to long to make sure that the addition
         and subtraction below (for overflow detection) are signed */
      while (MPFR_UNLIKELY(n > LONG_MAX))
        {
          int inex2;

          n -= LONG_MAX;
          inex2 = mpfr_mul_2ui(y, y, LONG_MAX, rnd_mode);
          if (inex2)
            return inex2; /* overflow */
        }

      /* MPFR_EMIN_MIN + (long) n is signed and doesn't lead to an overflow;
         the first test useful so that the real test can't lead to an
         overflow. */
      {
        mpfr_exp_t exp = MPFR_GET_EXP (y);
        if (MPFR_UNLIKELY( __gmpfr_emax < MPFR_EMIN_MIN + (long) n ||
                           exp > __gmpfr_emax - (long) n))
          return mpfr_overflow (y, rnd_mode, MPFR_SIGN(y));

        MPFR_SET_EXP (y, exp + (long) n);
      }
    }

  return inexact;
}