/* BD_Shape class implementation: non-inline functions.
   Copyright (C) 2001-2010 Roberto Bagnara <bagnara@cs.unipr.it>
   Copyright (C) 2010-2011 BUGSENG srl (http://bugseng.com)

This file is part of the Parma Polyhedra Library (PPL).

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

The PPL 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 General Public License
for more details.

You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software Foundation,
Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02111-1307, USA.

For the most up-to-date information see the Parma Polyhedra Library
site: http://www.cs.unipr.it/ppl/ . */

#include <ppl-config.h>
#include "BD_Shape.defs.hh"

namespace PPL = Parma_Polyhedra_Library;

#ifdef PPL_DOXYGEN_INCLUDE_IMPLEMENTATION_DETAILS
/*! \relates Parma_Polyhedra_Library::BD_Shape */
#endif // defined(PPL_DOXYGEN_INCLUDE_IMPLEMENTATION_DETAILS)
bool
PPL::extract_bounded_difference(const Constraint& c,
				const dimension_type c_space_dim,
				dimension_type& c_num_vars,
				dimension_type& c_first_var,
				dimension_type& c_second_var,
				Coefficient& c_coeff) {
  // Check for preconditions.
  PPL_ASSERT(c.space_dimension() == c_space_dim);
  PPL_ASSERT(c_num_vars == 0 && c_first_var == 0 && c_second_var == 0);
  // Store the indices of the non-zero components of `c',
  dimension_type non_zero_index[2] = { 0, 0 };
  // Collect the non-zero components of `c'.
  for (dimension_type i = c_space_dim; i-- > 0; )
    if (c.coefficient(Variable(i)) != 0) {
      if (c_num_vars <= 1)
	non_zero_index[c_num_vars++] = i + 1;
      else
	// Constraint `c' is not a bounded difference.
	return false;
    }

  // Make sure that `c' is indeed a bounded difference,
  // i.e., it has one of the following forms:
  //           0 <=/= b, if c_num_vars == 0;
  //   a*x       <=/= b, if c_num_vars == 1;
  //   a*x - a*y <=/= b, if c_num_vars == 2.
  switch (c_num_vars) {
  case 2:
    {
      const Coefficient& c0 = c.coefficient(Variable(non_zero_index[0]-1));
      const Coefficient& c1 = c.coefficient(Variable(non_zero_index[1]-1));
      if (sgn(c0) == sgn(c1) || c0 != -c1)
	// Constraint `c' is not a bounded difference.
	return false;
      c_coeff = c1;
    }
    c_first_var = non_zero_index[0];
    c_second_var = non_zero_index[1];
    break;
  case 1:
    c_coeff = -c.coefficient(Variable(non_zero_index[0]-1));
    c_first_var = non_zero_index[0];
    break;
  default:
    PPL_ASSERT(c_num_vars == 0);
    break;
  }
  return true;
}

#ifdef PPL_DOXYGEN_INCLUDE_IMPLEMENTATION_DETAILS
/*! \relates Parma_Polyhedra_Library::BD_Shape */
#endif // defined(PPL_DOXYGEN_INCLUDE_IMPLEMENTATION_DETAILS)
void
PPL::compute_leader_indices(const std::vector<dimension_type>& predecessor,
			    std::vector<dimension_type>& indices) {
  // The vector `indices' contains one entry for each equivalence
  // class, storing the index of the corresponding leader in
  // increasing order: it is used to avoid repeated tests for leadership.
  PPL_ASSERT(indices.size() == 0);
  PPL_ASSERT(0 == predecessor[0]);
  indices.push_back(0);
  for (dimension_type i = 1, p_size = predecessor.size(); i != p_size; ++i)
    if (i == predecessor[i])
      indices.push_back(i);
}