Message326917
> >>> from itertools import product
> >>> len(set(map(hash, product([0.5, 0.25], repeat=20))))
> 32
> Good catch! Would you like me to add this to the testsuite?
It's in mine already ;-) I've added all the "bad examples" in all the messages here. Sooner or later they'll get folded into Python's test suite.
BTW, there were no collisions in that under whatever 64-bit Python I last compiled. That was a SeaHash variant. I'm not certain, but I believe it had "t ^= t << 1" at the start and with the first multiply commented out.
Having learning _something_ about why SeaHash does what it does, I'm not convinced the first multiply is of much value. As a standalone bit-scrambler for a single 64-bit input, it does matter. But in the tuple hash context, we're running it in a loop. Strictly alternating "propagate left" and "propagate right" seems to me almost as good - although that's just intuition. |
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Date |
User |
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2018-10-02 21:41:39 | tim.peters | set | recipients:
+ tim.peters, rhettinger, mark.dickinson, eric.smith, jdemeyer, sir-sigurd |
2018-10-02 21:41:39 | tim.peters | set | messageid: <1538516499.17.0.545547206417.issue34751@psf.upfronthosting.co.za> |
2018-10-02 21:41:39 | tim.peters | link | issue34751 messages |
2018-10-02 21:41:39 | tim.peters | create | |
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