def hash64(key, seed):
hash_val = mmh3.hash64(key, seed)[<NUM_LIT:0>]<EOL>return struct.unpack('<STR_LIT>', struct.pack('<STR_LIT:q>', hash_val))[<NUM_LIT:0>]<EOL>
Wrapper around mmh3.hash64 to get us single 64-bit value.

This also does the extra work of ensuring that we always treat the
returned values as big-endian unsigned long, like smhasher used to
do.