Jeroen Demeyer <[email protected]> added the comment:
SeaHash seems to be designed for 64 bits. I'm guessing that replacing the
shifts by
x ^= ((x >> 16) >> (x >> 29))
would be what you'd do for a 32-bit hash. Alternatively, we could always
compute the hash with 64 bits (using uint64_t) and then truncate at the end if
needed.
However, when testing the hash function
for t in INPUT:
x ^= hash(t)
x *= MULTIPLIER
x ^= ((x >> 16) >> (x >> 29))
x *= MULTIPLIER
It fails horribly on the original and my new testsuite. I'm guessing that the
problem is that the line x ^= ((x >> 16) >> (x >> 29)) ignores low-order bits
of x, so it's too close to pure FNV which is known to have problems. When
replacing the first line of the loop above by x += hash(t) (DJB-style), it
becomes too close to pure DJB and it also fails horribly because of nested
tuples.
So it doesn't seem that the line x ^= ((x >> 16) >> (x >> 29)) (which is what
makes SeaHash special) really helps much to solve the known problems with DJB
or FNV.
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Python tracker <[email protected]>
<https://bugs.python.org/issue34751>
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