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bpo-43475: Fix worst case collision behavior for NaN instances #25493

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Merged
rhettinger merged 6 commits into from
Apr 22, 2021
Merged

bpo-43475: Fix worst case collision behavior for NaN instances #25493

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b9cde10
bpo-43475: Fix worst case collision behavior for NaN instances
rhettinger Apr 21, 2021
20b73c3
Fix decimal and docs as well
rhettinger Apr 21, 2021
056a4f7
Add casts
rhettinger Apr 21, 2021
dc73c3c
Use existing pointer hash logic
rhettinger Apr 21, 2021
9f3f9e9
Improve comment wording
rhettinger Apr 21, 2021
6ac6975
Fix typo in comment
rhettinger Apr 21, 2021
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@rhettinger
rhettinger committed Apr 21, 2021
commit 9f3f9e9373b222a330b91a9156116891f4d0bede
6 changes: 3 additions & 3 deletions Python/pyhash.c
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Expand Up @@ -59,9 +59,9 @@ static Py_ssize_t hashstats[Py_HASH_STATS_MAX + 1] = {0};
_PyHASH_INF and -_PyHASH_INF are also used for the
hashes of float and Decimal infinities.

NaNs hash to their object id. Having distinct hash values prevents
catastrophic piles-up for unique NaNs which used to always have
the same hash value but would compare unequal.
NaNs hash with a pointer hash. Having distinct hash values prevents
catastrophic pileups from distinct NaN instances which used to always
have the same hash value but would compare unequal.

A selling point for the above strategy is that it makes it possible
to compute hashes of decimal and binary floating-point numbers
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