message: fix fml for signalling NaN detection
diff: @@ -458,10 +458,10 @@ expr FloatType::isNaN(const expr &v, bool signalling) const {
  unsigned fraction_bits = bits() - exp_bits - 1;
  expr exponent = v.extract(fraction_bits + exp_bits - 1, fraction_bits);
  - expr nanqbit = exponent.extract(exp_bits - 1, exp_bits - 1);
  + expr nanqbit = v.extract(fraction_bits - 1, fraction_bits - 1);
  expr isqnan;
  if (signalling) {
  - expr fraction = v.extract(fraction_bits - 1, 0);
  + expr fraction = v.extract(fraction_bits - 2, 0);
  isqnan = nanqbit == 0 && fraction != 0;
  } else {
  isqnan = nanqbit == 1;
  