Message327063
>> 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. |
|
Date |
User |
Action |
Args |
2018-10-04 16:16:03 | tim.peters | set | recipients:
+ tim.peters, rhettinger, mark.dickinson, eric.smith, jdemeyer, sir-sigurd |
2018-10-04 16:16:03 | tim.peters | set | messageid: <1538669763.3.0.545547206417.issue34751@psf.upfronthosting.co.za> |
2018-10-04 16:16:03 | tim.peters | link | issue34751 messages |
2018-10-04 16:16:03 | tim.peters | create | |
|