Author tim.peters
Recipients eric.smith, jdemeyer, mark.dickinson, rhettinger, sir-sigurd, tim.peters
Date 2018-10-04.16:16:03
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Message-id <1538669763.3.0.545547206417.issue34751@psf.upfronthosting.co.za>
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>> In the 64-bit build there are no collisions across my
>> tests except for 11 in the new tuple test.

> That's pretty bad actually. With 64 bits, you statistically
> expect something in the order of 10**-8 collisions. So
> what you're seeing is 9 orders of magnitude too many collisions.

You wrote the test, so you should remember that you throw away the top 32 bits of the 64-bit hash code :-)  Tossing 345130 balls into 2**32 bins has an expected mean of 13.9 collisions and sdev 3.7.  11 collisions is fine.

If I change the test to retain all the hash bits in the 64-bit build, there are no collisions in the new tuple test.

If I change it again to retain only the high 32 hash bits, 27 collisions.  Which is statistically suspect, but still universes away from "disaster" territory.
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Date User Action Args
2018-10-04 16:16:03tim.peterssetrecipients: + tim.peters, rhettinger, mark.dickinson, eric.smith, jdemeyer, sir-sigurd
2018-10-04 16:16:03tim.peterssetmessageid: <1538669763.3.0.545547206417.issue34751@psf.upfronthosting.co.za>
2018-10-04 16:16:03tim.peterslinkissue34751 messages
2018-10-04 16:16:03tim.peterscreate