The nxt_murmur_hash2() generated 4-byte hash that was stored in uintptr_t,
which was 8 bytes long on 64-bit systems. At each iteration, it took the
previous key and hashed it again.
The problem was that it took only the first 4 bytes of the key, and these
4 bytes were always zero on 64-bit big-endian system. That resulted in
equal keys at each iteration.
The bug was discovered on IBM/S390x.
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