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bab.cc

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/*
 *  Main authors:
 *     Christian Schulte <schulte@gecode.org>
 *
 *  Copyright:
 *     Christian Schulte, 2003
 *
 *  Last modified:
 *     $Date: 2006-08-04 16:03:17 +0200 (Fri, 04 Aug 2006) $ by $Author: schulte $
 *     $Revision: 3511 $
 *
 *  This file is part of Gecode, the generic constraint
 *  development environment:
 *     http://www.gecode.org
 *
 *  See the file "LICENSE" for information on usage and
 *  redistribution of this file, and for a
 *     DISCLAIMER OF ALL WARRANTIES.
 *
 */

#include "gecode/search.hh"

namespace Gecode { namespace Search {

  /*
   * The invariant maintained by the engine is:
   *   For all nodes stored at a depth less than mark, there
   *   is no guarantee of betterness. For those above the mark,
   *   betterness is guaranteed.
   *
   * The engine maintains the path on the stack for the current
   * node to be explored.
   *
   */

  BabEngine::ExploreStatus
  BabEngine::explore(Space*& s1, Space*& s2) {
    start();
    /*
     * Upon entry, cur can be either NULL or set to the initial
     * space. For the initial case, es is also ES_CONSTRAIN.
     *
     * Otherwise (that is, cur == NULL), the actions depend on
     * es. In case es is ES_CONSTRAIN, a space on stack has been
     * constrained. Whether this is succesful recomputation finds
     * out. In any case, the stack is not allowed to be moved to
     * the next node.
     *
     * In case es is ES_SOLUTION, the stack must be moved to the next
     * node and recomputation is to be performed.
     */
    while (true) {
      assert((es == ES_SOLUTION) || (cur == NULL));
      if (stop(stacksize())) {
        s1 = NULL;
        return ES_SOLUTION;
      }
      if (cur == NULL) {
        if (es == ES_CONSTRAIN) {
          es = ES_SOLUTION;
          goto same;
        }
        do {
          if (!rcs.next(*this)) {
            s1 = NULL;
            return ES_SOLUTION;
          }
          {
            int l = rcs.lc(s1);
            if (l < mark) {
              es = ES_CONSTRAIN;
              mark = l;
              s2 = best;
              return ES_CONSTRAIN;
            }
          }
        same:
          cur = rcs.recompute<true>(d,*this);
        } while (cur == NULL);
        EngineCtrl::current(cur);
      }
      switch (cur->status(propagate)) {
      case SS_FAILED:
        fail++;
        delete cur;
        cur = NULL;
        EngineCtrl::current(NULL);
        break;
      case SS_SOLVED:
        delete best;
        best = cur;
        mark = rcs.entries();
        s1 = best->clone(true,propagate);
        clone++;
        cur = NULL;
        EngineCtrl::current(NULL);
        return ES_SOLUTION;
      case SS_BRANCH:
        {
          Space* c;
          if ((d == 0) || (d >= c_d)) {
            c = cur->clone(true,propagate);
            clone++;
            d = 1;
          } else {
            c = NULL;
            d++;
          }
          const BranchingDesc* desc = rcs.push(cur,c);
          EngineCtrl::push(c,desc);
          cur->commit(desc,0);
          commit++;
          break;
        }
      default:
        GECODE_NEVER;
      }
    }
    return ES_SOLUTION;
  }




  BAB::BAB(Space* s, unsigned int c_d, unsigned int a_d, Stop* st, size_t sz)
    : e(c_d,a_d,st,sz) {
    unsigned long int p = 0;
    Space* c = (s->status(p) == SS_FAILED) ? NULL : s->clone(true,p);
    e.init(c);
    e.propagate += p;
    e.current(s);
    e.current(NULL);
    e.current(c);
    if (c == NULL)
      e.fail += 1;
  }

  bool
  BAB::stopped(void) const {
    return e.stopped();
  }

  Statistics
  BAB::statistics(void) const {
    Statistics s = e;
    s.memory += e.stacksize();
    return s;
  }

}}

// STATISTICS: search-any