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Add a check for ASCII characters in to_upper and to_lower #81358

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Mar 17, 2021
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Add a check for ASCII characters in to_upper and to_lower #81358

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e48c684
Add a check for ASCII characters in to_upper and to_lower
mcastorina Jan 24, 2021
8acb566
Add to_lowercase and to_uppercase char benchmarks
mcastorina Jan 25, 2021
229fdf8
Add two more benchmarks for strictly ASCII and non ASCII cases
mcastorina Feb 3, 2021
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30 changes: 30 additions & 0 deletions library/core/benches/char/methods.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -45,3 +45,33 @@ fn bench_to_ascii_uppercase(b: &mut Bencher) {
fn bench_to_ascii_lowercase(b: &mut Bencher) {
b.iter(|| CHARS.iter().cycle().take(10_000).map(|c| c.to_ascii_lowercase()).min())
}

#[bench]
fn bench_ascii_mix_to_uppercase(b: &mut Bencher) {
b.iter(|| (0..=255).cycle().take(10_000).map(|b| char::from(b).to_uppercase()).count())

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Would it be possible to say anything about benchmarks results on mixed and non-ascii text? I expect branch prediction would mean that on pure non-ascii, there is virtually no change(?)

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I would expect so. What do you think of adding two more benchmarks for a total of three?

  • all ASCII characters
  • no ASCII characters
  • 50/50 mixed characters

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We need to be slightly careful here. The non-ascii benchmark is always one byte unicode is it not? It is non-ascii but above 192 it's going to be indicating another code point so there's going to be pleanty of malformed unicode in here.
It might be slightly better to create a random slice of u8 and then use String::from_utf8_lossy() to make it valid first?

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Since it's a benchmark I would want to make the "random chars" constant so runs can be compared.

What do you think of this? Playground Each test case can use the same list of chars and filter for what it's testing for (where mixed does no filtering).

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Random was the wrong choice of words here, sorry! It looks like a fair few other benchmarks / tests don't worry about putting in malformed utf sequences so I think it's fine to define the benchmarks this way for now.

}

#[bench]
fn bench_ascii_mix_to_lowercase(b: &mut Bencher) {
b.iter(|| (0..=255).cycle().take(10_000).map(|b| char::from(b).to_lowercase()).count())
}

#[bench]
fn bench_ascii_char_to_uppercase(b: &mut Bencher) {
b.iter(|| (0..=127).cycle().take(10_000).map(|b| char::from(b).to_uppercase()).count())
}

#[bench]
fn bench_ascii_char_to_lowercase(b: &mut Bencher) {
b.iter(|| (0..=127).cycle().take(10_000).map(|b| char::from(b).to_lowercase()).count())
}

#[bench]
fn bench_non_ascii_char_to_uppercase(b: &mut Bencher) {
b.iter(|| (128..=255).cycle().take(10_000).map(|b| char::from(b).to_uppercase()).count())
}

#[bench]
fn bench_non_ascii_char_to_lowercase(b: &mut Bencher) {
b.iter(|| (128..=255).cycle().take(10_000).map(|b| char::from(b).to_lowercase()).count())
}
20 changes: 14 additions & 6 deletions library/core/src/unicode/unicode_data.rs
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Expand Up @@ -549,16 +549,24 @@ pub mod white_space {
#[rustfmt::skip]
pub mod conversions {
pub fn to_lower(c: char) -> [char; 3] {
match bsearch_case_table(c, LOWERCASE_TABLE) {
None => [c, '\0', '\0'],
Some(index) => LOWERCASE_TABLE[index].1,
if c.is_ascii() {
[(c as u8).to_ascii_lowercase() as char, '\0', '\0']
} else {
match bsearch_case_table(c, LOWERCASE_TABLE) {
None => [c, '\0', '\0'],
Some(index) => LOWERCASE_TABLE[index].1,
}
}
}

pub fn to_upper(c: char) -> [char; 3] {
match bsearch_case_table(c, UPPERCASE_TABLE) {
None => [c, '\0', '\0'],
Some(index) => UPPERCASE_TABLE[index].1,
if c.is_ascii() {
[(c as u8).to_ascii_uppercase() as char, '\0', '\0']
} else {
match bsearch_case_table(c, UPPERCASE_TABLE) {
None => [c, '\0', '\0'],
Some(index) => UPPERCASE_TABLE[index].1,
}
}
}

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