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core/char: Speed up to_digit() for radix <= 10

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### Before

```
# Run 1
test char::methods::bench_to_digit_radix_10                ... bench:      16,265 ns/iter (+/- 1,774)
test char::methods::bench_to_digit_radix_16                ... bench:      13,938 ns/iter (+/- 2,479)
test char::methods::bench_to_digit_radix_2                 ... bench:      13,090 ns/iter (+/- 524)
test char::methods::bench_to_digit_radix_36                ... bench:      14,236 ns/iter (+/- 1,949)

# Run 2
test char::methods::bench_to_digit_radix_10                ... bench:      16,176 ns/iter (+/- 1,589)
test char::methods::bench_to_digit_radix_16                ... bench:      13,896 ns/iter (+/- 3,140)
test char::methods::bench_to_digit_radix_2                 ... bench:      13,158 ns/iter (+/- 1,112)
test char::methods::bench_to_digit_radix_36                ... bench:      14,206 ns/iter (+/- 1,312)

# Run 3
test char::methods::bench_to_digit_radix_10                ... bench:      16,221 ns/iter (+/- 2,423)
test char::methods::bench_to_digit_radix_16                ... bench:      14,361 ns/iter (+/- 3,926)
test char::methods::bench_to_digit_radix_2                 ... bench:      13,097 ns/iter (+/- 671)
test char::methods::bench_to_digit_radix_36                ... bench:      14,388 ns/iter (+/- 1,068)
```

### After

```
# Run 1
test char::methods::bench_to_digit_radix_10      ... bench:      11,521 ns/iter (+/- 552)
test char::methods::bench_to_digit_radix_16      ... bench:      12,926 ns/iter (+/- 684)
test char::methods::bench_to_digit_radix_2       ... bench:      11,266 ns/iter (+/- 1,085)
test char::methods::bench_to_digit_radix_36      ... bench:      14,213 ns/iter (+/- 614)

# Run 2
test char::methods::bench_to_digit_radix_10      ... bench:      11,424 ns/iter (+/- 1,042)
test char::methods::bench_to_digit_radix_16      ... bench:      12,854 ns/iter (+/- 1,193)
test char::methods::bench_to_digit_radix_2       ... bench:      11,193 ns/iter (+/- 716)
test char::methods::bench_to_digit_radix_36      ... bench:      14,249 ns/iter (+/- 3,514)

# Run 3
test char::methods::bench_to_digit_radix_10      ... bench:      11,469 ns/iter (+/- 685)
test char::methods::bench_to_digit_radix_16      ... bench:      12,852 ns/iter (+/- 568)
test char::methods::bench_to_digit_radix_2       ... bench:      11,275 ns/iter (+/- 1,356)
test char::methods::bench_to_digit_radix_36      ... bench:      14,188 ns/iter (+/- 1,501)
```
This commit is contained in:
Tobias Bieniek 2018-11-13 18:05:46 +01:00
parent 04aade83f2
commit 17f08fecfd
1 changed files with 20 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

25
src/libcore/char/methods.rs
View File

@ -122,12 +122,27 @@ impl char {
#[inline]
pub fn to_digit(self, radix: u32) -> Option<u32> {
assert!(radix <= 36, "to_digit: radix is too high (maximum 36)");
let val = match self {
'0' ..= '9' => self as u32 - '0' as u32,
'a' ..= 'z' => self as u32 - 'a' as u32 + 10,
'A' ..= 'Z' => self as u32 - 'A' as u32 + 10,
_ => return None,
if radix == 10 {
return match self {
'0' ..= '9' => Some(self as u32 - '0' as u32),
_ => None,
};
}
let val = if radix < 10 {
match self {
'0' ..= '9' => self as u32 - '0' as u32,
_ => return None,
}
} else {
match self {
'0'..='9' => self as u32 - '0' as u32,
'a'..='z' => self as u32 - 'a' as u32 + 10,
'A'..='Z' => self as u32 - 'A' as u32 + 10,
_ => return None,
}
};
if val < radix { Some(val) }
else { None }
}