eq.c
1.57 KB
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/* X eq Y */
static int fd_eq_filter(fd_constraint this)
{
int i;
// only propagate if culprit's domain is a singleton
for (i = 0; i < 2; ++i)
{
fd_int revise = VAR(this, 1 - i);
if (_fd_var_intersect(revise, VAR(this, i)))
{
if (fd_domain_empty(revise))
return FD_NOSOLUTION;
_fd_revise_connected(this, revise);
}
}
return FD_OK;
}
int fd_eq_propagate2(fd_constraint this, fd_int culprit)
{
fd_int revise;
int changed = 0;
revise = VAR(this, culprit == VAR(this, 0) ? 1 : 0);
changed = _fd_var_intersect(revise, culprit);
if (!changed)
return FD_OK;
if (fd_domain_empty(revise))
return FD_NOSOLUTION;
_fd_revise_connected(this, revise);
return FD_OK;
}
int fd_eq_propagate(fd_constraint this, fd_int revise)
{
fd_int other;
int changed = 0;
other = VAR(this, revise == VAR(this, 0) ? 1 : 0);
changed = _fd_var_intersect(revise, other);
if (changed && fd_domain_empty(revise))
return FD_NOSOLUTION;
// XXX: enqueue further updates here?
if (changed)
_fd_revise_connected(this, revise);
return FD_OK;
}
fd_constraint fd_eq(fd_int x, fd_int y)
{
fd_constraint c = _fd_constraint_new(2, 0);
if (c)
{
c->variables[0] = FD_INT2C_VAR(x); c->variables[1] = FD_INT2C_VAR(y);
#ifdef CONSTRAINT_CLASS
c->kind = FD_CONSTR_EQ;
#else /* CONSTRAINT_CLASS */
c->propagator2 = fd_eq_propagate2;
c->propagator = fd_eq_propagate;
#endif /* CONSTRAINT_CLASS */
_fd_var_add_constraint(x, c);
_fd_var_add_constraint(y, c);
_fd_add_constraint(c);
}
return c;
}