Only convert chars when needed in str case conversion methods. #52061
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Some of my assumptions seem to have been wrong. I really should have run these tests locally first 😓 |
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Jul 18, 2018
Handle array manually in str case conversion methods Avoiding the overhead incurred from `String.extend(char.to_lowercase())` showed a notable performance improvement when I benchmarked it. I tested on these strings: ```rust ALL_LOWER: "loremipsumdolorsitametduosensibusmnesarchumabcdefgh" ALL_UPPER: "LOREMIPSUMDOLORSITAMETDUOSENSIBUSMNESARCHUMABCDEFGH" REALISTIC_UPPER: "LOREM IPSUM DOLOR SIT AMET, DUO SENSIBUS MNESARCHUM" SIGMAS: "ΣΣΣΣΣ ΣΣΣΣΣ ΣΣΣΣΣ ΣΣΣ ΣΣΣΣ, ΣΣΣ ΣΣΣΣΣΣΣΣ ΣΣΣΣΣΣΣΣΣΣ" WORD_UPPER: "Lorem Ipsum Dolor Sit Amet, Duo Sensibus Mnesarchum" ``` the performance improvements of `to_lowercase()` were ``` running 10 tests test tests::all_lower ... bench: 1,752 ns/iter (+/- 49) test tests::all_lower_new ... bench: 1,266 ns/iter (+/- 15) -28% test tests::all_upper ... bench: 1,832 ns/iter (+/- 39) test tests::all_upper_new ... bench: 1,337 ns/iter (+/- 18) -27% test tests::realistic_upper ... bench: 1,993 ns/iter (+/- 14) test tests::realistic_upper_new ... bench: 1,445 ns/iter (+/- 22) -27% test tests::sigmas ... bench: 1,342 ns/iter (+/- 39) test tests::sigmas_new ... bench: 1,226 ns/iter (+/- 16) -9% test tests::word_upper ... bench: 1,899 ns/iter (+/- 12) test tests::word_upper_new ... bench: 1,381 ns/iter (+/- 26) -27% ``` and of `to_uppercase()` ``` running 10 tests test tests::all_lower ... bench: 1,813 ns/iter (+/- 20) test tests::all_lower_new ... bench: 1,321 ns/iter (+/- 16) -27% test tests::all_upper ... bench: 1,629 ns/iter (+/- 22) test tests::all_upper_new ... bench: 1,241 ns/iter (+/- 9) -24% test tests::realistic_upper ... bench: 1,670 ns/iter (+/- 24) test tests::realistic_upper_new ... bench: 1,241 ns/iter (+/- 17) -26% test tests::sigmas ... bench: 2,053 ns/iter (+/- 20) test tests::sigmas_new ... bench: 1,753 ns/iter (+/- 23) -15% test tests::word_upper ... bench: 1,873 ns/iter (+/- 30) test tests::word_upper_new ... bench: 1,412 ns/iter (+/- 25) -25% ``` I gave up on the more advanced method from rust-lang#52061 as it wasn't always a clear improvement and would help in even less cases if this PR was merged.
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Optimizes
str.to_lowercase()andstr.to_uppercase()by appending slices of correct characters to the new string instead of inserting them individually.I benched these changes (file) with these simple test cases:
These were the results of the change to
to_uppercase():And these were the results of the change to
to_lowercase():So an improvement across the board, except for,
all_upper_lowercaseandall_lower_uppercase, where every single character had to be converted. I think that's a fair trade considering the gain in performance is pretty large in many other cases.