/* sub.c -- Subtract two intervals.

Copyright 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2010,
                     Spaces project, Inria Lorraine
                     and Salsa project, INRIA Rocquencourt,
                     and Arenaire project, Inria Rhone-Alpes, France
                     and Lab. ANO, USTL (Univ. of Lille),  France

This file is part of the MPFI Library.

The MPFI 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 MPFI 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 MPFI 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 "mpfi-impl.h"

int
mpfi_sub (mpfi_ptr a, mpfi_srcptr b, mpfi_srcptr c)
{
  mpfr_t tmp;
  int inexact_left, inexact_right, inexact = 0;

  if (MPFI_IS_ZERO (c)) {
    return mpfi_set (a, b);
  }
  else if (MPFI_IS_ZERO (b)) {
    return mpfi_neg (a, c);
  }
  else {
    mpfr_init2 (tmp, mpfr_get_prec (&(a->left)));
    inexact_left = mpfr_sub (tmp, &(b->left), &(c->right), MPFI_RNDD);
    inexact_right = mpfr_sub (&(a->right), &(b->right), &(c->left), MPFI_RNDU);
    mpfr_set (&(a->left), tmp, MPFI_RNDD); /* exact */
    mpfr_clear (tmp);

    /* do not allow -0 as lower bound */
    if (mpfr_zero_p (&(a->left)) && mpfr_signbit (&(a->left))) {
      mpfr_neg (&(a->left), &(a->left), MPFI_RNDU);
    }
    /* do not allow +0 as upper bound */
    if (mpfr_zero_p (&(a->right)) && !mpfr_signbit (&(a->right))) {
      mpfr_neg (&(a->right), &(a->right), MPFI_RNDD);
    }

    if (MPFI_NAN_P (a))
      MPFR_RET_NAN;
    if (inexact_left)
      inexact += 1;
    if (inexact_right)
      inexact += 2;

    return inexact;
  }
}
