mozilla/rust — pull request #14135 by gereeter (2014-05-12 12:11:52+00:00)
Title: Optimize string searching using two way search (WIP)

This changes the previously naive string searching algorithm to a two-way search like glibc, which should be faster on average while still maintaining worst case linear time complexity. This fixes #14107. Note that I don't think this should be merged yet, as this is the only approach to speeding up search I've tried - it's worth considering options like Boyer-Moore or adding a bad character shift table to this. However, the benchmarks look quite good so far:

test str::bench::bench_contains_bad_naive ... bench: 290 ns/iter (+/- 12) from 1309 ns/iter (+/- 36)
test str::bench::bench_contains_equal ... bench: 479 ns/iter (+/- 10) from 137 ns/iter (+/- 2)
test str::bench::bench_contains_short_long ... bench: 2844 ns/iter (+/- 105) from 5473 ns/iter (+/- 14)
test str::bench::bench_contains_short_short ... bench: 55 ns/iter (+/- 4) from 57 ns/iter (+/- 6)

Except for the case specifically designed to be optimal for the naive case (`bench_contains_equal`), this gets as good or better performance as the previous code.