// Ref: Boost lib, container_hash/hash.hpp
private static void HashCombine(ref uint h1, uint k1)
{
const uint c1 = 0xcc9e2d51;
const uint c2 = 0x1b873593;
k1 *= c1;
k1 = Util.Rotl32(k1, 15);
k1 *= c2;
h1 ^= k1;
h1 = Util.Rotl32(h1, 13);
h1 = h1 * 5 + 0xe6546b64;
}