[DO NOT MERGE]: Try out 128bit SipHash for incr. comp. hashes.

[michaelwoerister]

This is just for performance testing on perf.rust-lang.org. It's not meant to be merged in this state.

[rust-highfive]

r? @arielb1

(rust_highfive has picked a reviewer for you, use r? to override)

[michaelwoerister]

Btw, this contains a copy of @arthurprs excellent metrohash implementation (had to copy it because finish128 is not public). In my local tests this was the best performing hash function I found on crates.io.

[michaelwoerister]

@bors try

[bors]

⌛ Trying commit 85a12ea with merge 0ea9f24...

[arthurprs]

Thanks for the ping, I'm always interesting in these changes. The faster the merrier 😄

Can perf.rust-lang.org test unmerged PRs? That's really nice.

[bors]

☀️ Test successful - status-travis
State: approved= try=True

[Mark-Simulacrum]

http://perf.rust-lang.org/compare.html?commit_a=fd8099f0ecc2fd3980469ec45cf834ae9a941ca3&commit_b=0ea9f24fb9ec914e29f759b5e1ede9fcd496a1d5&stat=instructions%3Au

[michaelwoerister]

Thanks a lot, @Mark-Simulacrum!

This is the fairer comparison:
http://perf.rust-lang.org/compare.html?commit_a=d7e73e4b1abe120520d1894b89c0e25469f41e69&commit_b=0ea9f24fb9ec914e29f759b5e1ede9fcd496a1d5&stat=instructions%3Au

[michaelwoerister]

Closing, see follow-up here: #41215 (comment)