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eqv.cpp
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1 /* -*- mode: C++; c-basic-offset: 2; indent-tabs-mode: nil -*- */
2 /*
3  * Main authors:
4  * Christian Schulte <schulte@gecode.org>
5  *
6  * Copyright:
7  * Christian Schulte, 2011
8  *
9  * Last modified:
10  * $Date: 2011-10-07 20:28:27 +1100 (Fri, 07 Oct 2011) $ by $Author: schulte $
11  * $Revision: 12427 $
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37 
38 #include <gecode/int/bool.hh>
39 
40 namespace Gecode { namespace Int { namespace Bool {
41 
42  /*
43  * N-ary Boolean equivalence propagator
44  *
45  */
46 
47  PropCost
48  NaryEqv::cost(const Space&, const ModEventDelta&) const {
50  }
51 
52  Actor*
53  NaryEqv::copy(Space& home, bool share) {
54  return new (home) NaryEqv(home,share,*this);
55  }
56 
58  NaryEqv::post(Home home, ViewArray<BoolView>& x, int pm2) {
59  int n = x.size();
60  for (int i=n; i--; )
61  if (x[i].assigned()) {
62  pm2 ^= x[i].val();
63  x[i] = x[--n];
64  }
65  if (n == 0)
66  return (pm2 == 1) ? ES_OK : ES_FAILED;
67  if (n == 1) {
68  GECODE_ME_CHECK(x[0].eq(home,1^pm2));
69  return ES_OK;
70  }
71  if (n == 2) {
72  if (pm2 == 1) {
73  return Bool::Eq<BoolView,BoolView>::post(home,x[0],x[1]);
74  } else {
75  NegBoolView n(x[1]);
76  return Bool::Eq<BoolView,NegBoolView>::post(home,x[0],n);
77  }
78  }
79  x.size(n);
80  (void) new (home) NaryEqv(home,x,pm2);
81  return ES_OK;
82  }
83 
86  resubscribe(home,x0);
87  resubscribe(home,x1);
88  if (x.size() == 0) {
89  if (x0.assigned() && x1.assigned()) {
90  return (pm2 == 1) ? home.ES_SUBSUMED(*this) : ES_FAILED;
91  } else if (x0.assigned()) {
92  GECODE_ME_CHECK(x1.eq(home,1^pm2));
93  return home.ES_SUBSUMED(*this);
94  } else if (x1.assigned()) {
95  GECODE_ME_CHECK(x0.eq(home,1^pm2));
96  return home.ES_SUBSUMED(*this);
97  }
98  }
99  return ES_FIX;
100  }
101 
102 }}}
103 
104 // STATISTICS: int-prop