xxh_rotl32
h32 = xxh_rotl32(v1, 1) + xxh_rotl32(v2, 7) +
xxh_rotl32(v3, 12) + xxh_rotl32(v4, 18);
h32 = xxh_rotl32(h32, 17) * PRIME32_4;
h32 = xxh_rotl32(h32, 11) * PRIME32_1;
seed = xxh_rotl32(seed, 13);