element-var.c
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/* element-var */
/* element-var(X, y, z) == X[y] = z (0 <= y < |X|) */
static int fd_element_var_filter(fd_constraint this)
{
int length = this->nvariables - 2;
fd_int index, value;
int imax, min, max;
int v;
int i;
// do some filtering...
index = VAR(this, this->nvariables - 2);
// check the index variable
if (_fd_var_del_ge(length, index))
{
if (fd_domain_empty(index))
return FD_NOSOLUTION;
_fd_revise_connected(this, index);
}
value = VAR(this, this->nvariables - 1);
// see if the index is already fixed
if (fd_var_single(index, &v))
{
if (_fd_var_intersect(VAR(this, v), value))
{
if (fd_domain_empty(VAR(this, v)))
return FD_NOSOLUTION;
_fd_revise_connected(this, VAR(this, v));
}
if (_fd_var_intersect(value, VAR(this, v)))
{
if (fd_domain_empty(value))
return FD_NOSOLUTION;
_fd_revise_connected(this, value);
}
return FD_OK;
}
// do some bounds filtering on the value variable
imax = _fd_var_max(index);
min = _fd_var_min(VAR(this, imax));
max = _fd_var_max(VAR(this, imax));
for (i = _fd_var_min(index); i < imax; ++i)
{
int m;
if ((m = _fd_var_min(VAR(this, i))) < min)
min = m;
else if ((m = _fd_var_max(VAR(this, i))) > max)
max = m;
}
if (_fd_var_del_lt(min, value) | _fd_var_del_gt(max, value))
{
if (fd_domain_empty(value))
return FD_NOSOLUTION;
_fd_revise_connected(this, value);
}
// XXX: more...
return FD_OK;
}
static int fd_element_var_propagate2(fd_constraint this, fd_int culprit)
{
int length = this->nvariables - 2;
fd_int index, value;
int i;
// do some filtering...
index = VAR(this, this->nvariables - 2);
value = VAR(this, this->nvariables - 1);
// see if the culprit is the index variable
if (culprit == index)
{
if (fd_var_single(index, &i))
{
if (_fd_var_intersect(VAR(this, i), value))
{
if (fd_domain_empty(VAR(this, i)))
return FD_NOSOLUTION;
_fd_revise_connected(this, VAR(this, i));
}
if (_fd_var_intersect(value, VAR(this, i)))
{
if (fd_domain_empty(value))
return FD_NOSOLUTION;
_fd_revise_connected(this, value);
}
}
return FD_OK;
}
// see if the culprit is the value variable
if (culprit == value)
{
int k;
if (fd_var_single(value, &k))
{
// check which variables have k in their domain
int imax = _fd_var_max(index);
for (i = _fd_var_min(index); i <= imax; ++i)
if (!_fd_var_contains_val(VAR(this, i), k) &&
_fd_var_del_val(i, index))
{
if (fd_domain_empty(index))
return FD_NOSOLUTION;
_fd_revise_connected(NULL, index);
}
}
return FD_OK;
}
// XXX: filter for non-index and non-value variables
return FD_OK;
}
fd_constraint fd_element_var(fd_int *variables, int nvariables, fd_int index,
fd_int value)
{
fd_constraint c = _fd_constraint_new(nvariables + 2, 0);
int i;
// XXX: add a constraint 0 <= INDEX < nvariables
if (c)
{
for (i = 0; i < nvariables; ++i)
c->variables[i] = FD_INT2C_VAR(variables[i]);
c->variables[nvariables] = FD_INT2C_VAR(index);
c->variables[nvariables + 1] = FD_INT2C_VAR(value);
#ifdef CONSTRAINT_CLASS
c->kind = FD_CONSTR_ELEMENT_VAR;
#else /* CONSTRAINT_CLASS */
c->propagator2 = fd_element_var_propagate2;
#endif /* CONSTRAINT_CLASS */
for (i = 0; i < c->nvariables; ++i)
_fd_var_add_constraint(VAR(c, i), c);
_fd_add_constraint(c);
}
return c;
}