Question

Is there any function in the GMP library which give me bitLength of any GMP variable?

mpz_t temp;
mpz_init(temp);
mpz_set_ui(temp,356678789);

Then how to find bitlength of temp?

Answer 1

Perhaps there is a better, way, but after reading the docs I came up with this one:

mp_bitcnt_t msb(mpz_t& m) {
  mpz_t n = m.get_moz_t();
  mp_bitcnt_t remaining = mpz_popcount(n), last = -1;
  while (remaining) {
    --remaining;
    last = mpz_scan1(n, last + 1);
  }
  return last;
}