#include <errno.h>
#include <signal.h>

int sigaddset(sigset_t* set, int sig) {
  unsigned s = sig - 1;
  if (s >= _NSIG - 1 || sig - 32U < 3) {
    errno = EINVAL;
    return -1;
  }
  set->__bits[s / 8 / sizeof *set->__bits] |= 1UL << (s & (8 * sizeof *set->__bits - 1));
  return 0;
}