int check_signatures(msg_hash, signatures, signers, bitmask_size) impure {
  var bitmask = 0;
  var id = -1;
  do {
    (id, var signature, var f) = signatures.udict_get_next?(32, id);
    if (f){
      var sig = signature.preload_bits(512);
      var public_key = -1;
      do {
        (public_key, var cs, var _found) = signers.udict_get_next?(256, public_key);
        if (_found){
          if (check_signature(msg_hash, sig, public_key)){
            var signer_index = cs~load_uint(bitmask_size);
                    bitmask = bitmask | (1 << (signer_index - 1));  
          } 
        }
      } until (~ _found);
      ;; signature~touch(); 
    }
  } until (~ f);
  return bitmask;
}