Hash_prefix
Hash_prefix(x, 3, r, Small_bytes);
Hash_prefix(h, 2, x, sizeof x);
Hash_prefix(x, 3, y, Small_bytes);
Hash_prefix(k, b, x, sizeof x);
Hash_prefix(sk + Small_bytes, 4, pk, crypto_kem_sntrup761_PUBLICKEYBYTES);
Hash_prefix(cache, 4, pk, crypto_kem_sntrup761_PUBLICKEYBYTES);