[Python-Dev] String hash function multiplier (original) (raw)

Guido van Rossum guido at python.org
Tue Apr 13 23:25:03 EDT 2004

Does anyone have any issues with changing the hash multiplier for the string and Unicode hash functions?

Instead of 1000003, I would like to use Aho's 65599, a prime near 2**16 that is efficiently expressible as (x << 6) + (x << 16) - x. This replaces a multiply with fast adds and shifts (with the two shifts potentially being executed in parallel). Googling for "hash 65599" shows a long history of widespread use and testing without any problems.

It would break the parrot benchmark, which has a re-implementation of the hash in Python and assumes/checks at various points that the two agree.

So I'd rather not see this changed before July 30.

--Guido van Rossum (home page: http://www.python.org/~guido/)

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