/* mpfr_div_2ui -- divide a floating-point number by a power of two

Copyright 1999, 2001, 2002, 2003, 2004, 2005, 2006 Free Software Foundation, Inc.

This file is part of the MPFR Library.

The 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 2.1 of the License, or (at your
option) any later version.

The 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 MPFR Library; see the file COPYING.LIB.  If not, write to
the Free Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston,
MA 02110-1301, USA. */

#include "mpfr-impl.h"

int
mpfr_div_2ui (mpfr_ptr y, mpfr_srcptr x, unsigned long n, mp_rnd_t rnd_mode)
{
  int inexact;

  /* Most of the times, this function is called with y==x */
  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_div_2ui(y, y, LONG_MAX, rnd_mode);
          if (inex2)
            return inex2; /* underflow */
        }

      /* MPFR_EMAX_MAX - (long) n is signed and doesn't lead to an integer
         overflow; the first test useful so that the real test can't lead
         to an integer overflow. */
      {
        mp_exp_t exp = MPFR_GET_EXP (y);
        if (MPFR_UNLIKELY( __gmpfr_emin > MPFR_EMAX_MAX - (long) n ||
                           exp < __gmpfr_emin + (long) n) )
          {
            if (rnd_mode == GMP_RNDN &&
                (__gmpfr_emin > MPFR_EMAX_MAX - (long) (n - 1) ||
                 exp < __gmpfr_emin + (long) (n - 1) ||
                 mpfr_powerof2_raw (y)))
              rnd_mode = GMP_RNDZ;
            return mpfr_underflow (y, rnd_mode, MPFR_SIGN(y));
          }

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

  return inexact;
}