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eqv.cpp

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00001 /* -*- mode: C++; c-basic-offset: 2; indent-tabs-mode: nil -*- */
00002 /*
00003  *  Main authors:
00004  *     Christian Schulte <schulte@gecode.org>
00005  *
00006  *  Copyright:
00007  *     Christian Schulte, 2011
00008  *
00009  *  Last modified:
00010  *     $Date: 2011-10-07 11:28:27 +0200 (Fri, 07 Oct 2011) $ by $Author: schulte $
00011  *     $Revision: 12427 $
00012  *
00013  *  This file is part of Gecode, the generic constraint
00014  *  development environment:
00015  *     http://www.gecode.org
00016  *
00017  *  Permission is hereby granted, free of charge, to any person obtaining
00018  *  a copy of this software and associated documentation files (the
00019  *  "Software"), to deal in the Software without restriction, including
00020  *  without limitation the rights to use, copy, modify, merge, publish,
00021  *  distribute, sublicense, and/or sell copies of the Software, and to
00022  *  permit persons to whom the Software is furnished to do so, subject to
00023  *  the following conditions:
00024  *
00025  *  The above copyright notice and this permission notice shall be
00026  *  included in all copies or substantial portions of the Software.
00027  *
00028  *  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
00029  *  EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
00030  *  MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
00031  *  NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
00032  *  LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
00033  *  OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
00034  *  WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
00035  *
00036  */
00037 
00038 #include <gecode/int/bool.hh>
00039 
00040 namespace Gecode { namespace Int { namespace Bool {
00041 
00042   /*
00043    * N-ary Boolean equivalence propagator
00044    *
00045    */
00046 
00047   PropCost
00048   NaryEqv::cost(const Space&, const ModEventDelta&) const {
00049     return PropCost::binary(PropCost::LO);
00050   }
00051 
00052   Actor*
00053   NaryEqv::copy(Space& home, bool share) {
00054     return new (home) NaryEqv(home,share,*this);
00055   }
00056 
00057   ExecStatus
00058   NaryEqv::post(Home home, ViewArray<BoolView>& x, int pm2) {
00059     int n = x.size();
00060     for (int i=n; i--; )
00061       if (x[i].assigned()) {
00062         pm2 ^= x[i].val();
00063         x[i] = x[--n];
00064       }
00065     if (n == 0)
00066       return (pm2 == 1) ? ES_OK : ES_FAILED;
00067     if (n == 1) {
00068       GECODE_ME_CHECK(x[0].eq(home,1^pm2));
00069       return ES_OK;
00070     }
00071     if (n == 2) {
00072       if (pm2 == 1) {
00073         return Bool::Eq<BoolView,BoolView>::post(home,x[0],x[1]);
00074       } else {
00075         NegBoolView n(x[1]);
00076         return Bool::Eq<BoolView,NegBoolView>::post(home,x[0],n);
00077       }
00078     }
00079     x.size(n);
00080     (void) new (home) NaryEqv(home,x,pm2);
00081     return ES_OK;
00082   }
00083 
00084   ExecStatus
00085   NaryEqv::propagate(Space& home, const ModEventDelta&) {
00086     resubscribe(home,x0);
00087     resubscribe(home,x1);
00088     if (x.size() == 0) {
00089       if (x0.assigned() && x1.assigned()) {
00090         return (pm2 == 1) ? home.ES_SUBSUMED(*this) : ES_FAILED;
00091       } else if (x0.assigned()) {
00092         GECODE_ME_CHECK(x1.eq(home,1^pm2));
00093         return home.ES_SUBSUMED(*this);
00094       } else if (x1.assigned()) {
00095         GECODE_ME_CHECK(x0.eq(home,1^pm2));
00096         return home.ES_SUBSUMED(*this);
00097       }
00098     }
00099     return ES_FIX;
00100   }
00101 
00102 }}}
00103 
00104 // STATISTICS: int-prop