Function antiDos

src/simplicity/eval.c:534–555

Inspects the stack contents after a successful runTCO execution to verify anti-DOS properties: * 1. If 'checks' includes 'CHECK_EXEC', then check that all non-HIDDEN dag nodes were executed at least once. * 2. If 'checks' includes 'CHECK_CASE', then check that both branches of every CASE node were executed. * * If these are violated, it means that the dag had unpruned nodes. * * Returns 'SIM

 *               dag_node dag[len];
 */
static simplicity_err antiDos(flags_type checks, const call* stack, const dag_node* dag, size_t len) {
  static_assert(CHECK_EXEC == FLAG_EXEC, "CHECK_EXEC does not match FLAG_EXEC");
  static_assert(CHECK_CASE == (FLAG_CASE_LEFT | FLAG_CASE_RIGHT), "CHECK_CASE does not match FLAG_CASE");
  simplicity_assert(CHECK_CASE == (checks & CHECK_CASE) || 0 == (checks & CHECK_CASE));

  if (!checks) return SIMPLICITY_NO_ERROR;

  for(size_t i = 0; i < len; ++i) {
    /* All non-HIDDEN nodes must be executed at least once. */
    /* Both branches of every case combinator must be executed at least once. */
    flags_type test_flags = (HIDDEN != dag[i].tag ? CHECK_EXEC : 0)
                          | (CASE == dag[i].tag ? CHECK_CASE : 0);

    /* Only enable requested checks */
    test_flags &= checks;
    if (test_flags != (test_flags & stack[i].flags)) {
      return SIMPLICITY_ERR_ANTIDOS;
    }
  }

  return SIMPLICITY_NO_ERROR;
}

/* This structure is used by the static analysis that computes bounds on the working memory that suffices for
 * the Simplicity interpreter, and the CPU cost bounds in milliWU