http://datagenetics.com/blog/december12014/index.html

parity.cpp

#include <iostream>
#include <random>
#include <cassert>
#include <cstdint>

static int odd_bits(std::uint64_t i) {
  auto a = (0xFFFFFFFFu & i) ^ (i >> 32);
  auto b = (0x0000FFFFu & a) ^ (a >> 16);
  auto c = (0x000000FFu & b) ^ (b >> 8);
  auto d = (0x0000000Fu & c) ^ (c >> 4);
  auto e = (0x00000003u & d) ^ (d >> 2);
  auto f = (0x00000001u & e) ^ (e >> 1);
  return f;
}

static int parity(std::uint64_t i) {
  return odd_bits(i & 0xFFFFFFFF00000000u) << 5 |
         odd_bits(i & 0xFFFF0000FFFF0000u) << 4 |
         odd_bits(i & 0xFF00FF00FF00FF00u) << 3 |
         odd_bits(i & 0xF0F0F0F0F0F0F0F0u) << 2 |
         odd_bits(i & 0xCCCCCCCCCCCCCCCCu) << 1 |
         odd_bits(i & 0xAAAAAAAAAAAAAAAAu) << 0;
}

static std::uint64_t flip_bit(std::uint64_t i, int bit) {
	return i ^ (1ull << bit);
}

int main() {
	std::mt19937 eng;
	std::uniform_int_distribution<std::uint64_t> dist;
	std::uniform_int_distribution<int> rand_parity(0, 63);
	std::cout << std::hex;
	for (int i = 0; i < 10; ++i) {
		auto x = dist(eng);
		std::cout << x << ' ' << parity(x) << " : ";
		auto b = rand_parity(eng);
		auto y = flip_bit(x, parity(x) ^ b);
		std::cout << b << " : ";
		std::cout << y << ' ' << parity(y) << '\n';
	}
}