Set-update-extract

Example:

// Consider only low part
rule(a, b) {
  tmp = set_low_part(a);
  tmp = update_high(tmp, b)
  return extract_low(tmp);
} -> {
  return a;
}
// Consider only high part
rule(a, b) {
  tmp = set_low_part(a);
  tmp = update_high(tmp, b)
  return extract_high(tmp);
} -> {
  return b;
}