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/* mpfr_ui_sub -- subtract a floating-point number from an integer

Copyright 2000, 2001, 2002 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., 59 Temple Place - Suite 330, Boston,
MA 02111-1307, USA. */

#include "gmp.h"
#include "gmp-impl.h"
#include "longlong.h"
#include "mpfr.h"
#include "mpfr-impl.h"

int
mpfr_ui_sub (mpfr_ptr y, unsigned long int u, mpfr_srcptr x, mp_rnd_t rnd_mode)
{
  mpfr_t uu;
  mp_limb_t up[1];
  unsigned long cnt;
  
  if (MPFR_IS_NAN(x)) 
    {
      MPFR_SET_NAN(y);
      MPFR_RET_NAN;
    }

  MPFR_CLEAR_NAN(y);

  if (MPFR_IS_INF(x))
    {
      MPFR_SET_INF(y);
      if (MPFR_SIGN(x) == MPFR_SIGN(y))
	MPFR_CHANGE_SIGN(y);
      MPFR_RET(0); /* +/-infinity is exact */
    }

  if (u) {
    MPFR_INIT1 (up, uu, BITS_PER_MP_LIMB, 1);
    count_leading_zeros (cnt, (mp_limb_t) u);
    *up = (mp_limb_t) u << cnt;
    MPFR_EXP(uu) = BITS_PER_MP_LIMB - cnt;
  
    return mpfr_sub (y, uu, x, rnd_mode);
  }
  else
    return mpfr_neg (y, x, rnd_mode); /* if u=0, then set y to -x */
}