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authorEduard-Mihai Burtescu <edy.burt@gmail.com>2017-02-25 14:13:26 +0200
committerGitHub <noreply@github.com>2017-02-25 14:13:26 +0200
commitd78a7fcea4d801a070f7848835f63dd8e6c5fa97 (patch)
tree2265030813fb0ea4b9a1c303af136056bd9f500b /src/test/incremental/thinlto
parent33c19129c363eae3b84bdcc0fdf632f211dbd26a (diff)
parent25b14889186b5e67906efe65a368ca75a69f6c20 (diff)
downloadrust-d78a7fcea4d801a070f7848835f63dd8e6c5fa97.tar.gz
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Rollup merge of #39988 - arthurprs:hm-adapt2, r=alexcrichton
Simplify/fix adaptive hashmap

Please see https://github.com/rust-lang/rust/pull/38368#issuecomment-280957863 for context.

The shift length math is broken. It turns out that checking for the shift length is complicated. Using simulations it's possible to see that a value of 2000 will only get probabilities down to ~1e-7 when the hashmap load factor is 90% (rust goes up to 90.9% as of today). That's probably not good enough to go into the stdlib with pluggable hashers.

So this PR simplify the adaptive behavior to only consider displacement, which is much safer and very useful by itself.

There's two comments because one of them is already being tested to be merged by bors.
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