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src/constraints/lt.c 2.4 KB
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/* x < y */
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static int fd_lt_filter(fd_constraint this)
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{
  fd_int x, y;

  x = VAR(this, 0);
  y = VAR(this, 1);

#ifndef DISABLE_ENTAILED
  if (_fd_var_max(x) < _fd_var_min(y))
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    {
      fd__constraint_set_entailed(this);

      return FD_OK;
    }
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#endif

  if (_fd_var_del_le(_fd_var_min(x), y))
    {
      if (fd_domain_empty(y))
	return FD_NOSOLUTION;
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      _fd_revise_connected(this, y);
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    }

  if (_fd_var_del_ge(_fd_var_max(y), x))
    {
      if (fd_domain_empty(x))
	return FD_NOSOLUTION;
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      _fd_revise_connected(this, x);
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    }
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#ifndef DISABLE_ENTAILED
  if (_fd_var_max(x) < _fd_var_min(y))
    fd__constraint_set_entailed(this);
#endif
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  return FD_OK;
}
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static int fd_lt_propagate2(fd_constraint this, fd_int culprit)
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{
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  fd_int x, y;
  int vmax, vmin;
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  fd_int revise;
  int changed = 0;
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  x = VAR(this, 0);
  y = VAR(this, 1);

#ifndef DISABLE_ENTAILED
  vmax = _fd_var_max(x);
  vmin = _fd_var_min(y);

  if (vmax < vmin)
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    {
      fd__constraint_set_entailed(this);

      return FD_OK;
    }
#endif
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  if (culprit == x)
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    {
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      revise = y;
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      vmin = _fd_var_min(x);

      changed = _fd_var_del_le(vmin, y);
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    }
  else
    {
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      revise = x;
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      vmax = _fd_var_max(y);
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      changed = _fd_var_del_ge(vmax, x);
    }
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  if (changed)
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    {
      if (fd_domain_empty(revise))
	return FD_NOSOLUTION;

      _fd_revise_connected(this, revise);

#ifndef DISABLE_ENTAILED
      // see if the culprit's domain is a singleton
      if (vmin == vmax)
	fd__constraint_set_entailed(this);
#endif
    }
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  return FD_OK;
}
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static int fd_lt_propagate(fd_constraint this, fd_int revise)
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{
  int changed = 0;

  if (revise == VAR(this, 0))
    changed = _fd_var_del_ge(_fd_var_max(VAR(this, 1)), revise);
  else
    changed = _fd_var_del_le(_fd_var_min(VAR(this, 0)), revise);

  if (changed && fd_domain_empty(revise))
    return FD_NOSOLUTION;

#ifdef USE_ENTAILED
  if (_fd_var_max(VAR(this, 0)) < _fd_var_min(VAR(this, 1)))
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    fd__constraint_set_entailed(this);
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#endif

  // XXX: enqueue further updates here?
  if (changed)
    _fd_revise_connected(this, revise);

  return FD_OK;
}

fd_constraint fd_lt(fd_int x, fd_int y)
{
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  fd_constraint c = fd__constraint_new(2, 0);
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  if (c)
    {
      c->variables[0] = FD_INT2C_VAR(x); c->variables[1] = FD_INT2C_VAR(y);
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      c->kind = FD_CONSTR_LT;
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      _fd_var_add_constraint(x, c);
      _fd_var_add_constraint(y, c);

      _fd_add_constraint(c);
    }

  return c;
}