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ToBase64 and ToHex perf improvements

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The overhead of str::push_char is high enough to cripple the performance
of these two functions. I've switched them to build the output in a
~[u8] and then convert to a string later. Since we know exactly the
bytes going into the vector, we can use the unsafe version to avoid the
is_utf8 check.

I could have riced it further with vec::raw::get, but it only added
~10MB/s so I didn't think it was worth it. ToHex is still ~30% slower
than FromHex, which is puzzling.

Before:

```
test base64::test::from_base64 ... bench: 1000 ns/iter (+/- 349) = 204 MB/s
test base64::test::to_base64 ... bench: 2390 ns/iter (+/- 1130) = 63 MB/s
...
test hex::tests::bench_from_hex ... bench: 884 ns/iter (+/- 220) = 341 MB/s
test hex::tests::bench_to_hex ... bench: 2453 ns/iter (+/- 919) = 61 MB/s
```

After:

```
test base64::test::from_base64 ... bench: 1271 ns/iter (+/- 600) = 160 MB/s
test base64::test::to_base64 ... bench: 759 ns/iter (+/- 286) = 198 MB/s
...
test hex::tests::bench_from_hex ... bench: 875 ns/iter (+/- 377) = 345 MB/s
test hex::tests::bench_to_hex ... bench: 593 ns/iter (+/- 240) = 254 MB/s
```
This commit is contained in:
Steven Fackler 2013-08-04 23:51:26 -04:00
parent 463e2416e9
commit ff5fdffc13
2 changed files with 37 additions and 36 deletions
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14
src/libextra/hex.rs
View file

@ -19,8 +19,7 @@ pub trait ToHex {
fn to_hex(&self) -> ~str;
}
static CHARS: [char, ..16] = ['0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
'a', 'b', 'c', 'd', 'e', 'f'];
static CHARS: &'static[u8] = bytes!("0123456789abcdef");
impl<'self> ToHex for &'self [u8] {
/**
@ -39,13 +38,16 @@ impl<'self> ToHex for &'self [u8] {
* ~~~
*/
fn to_hex(&self) -> ~str {
let mut s = str::with_capacity(self.len() * 2);
// +1 for NULL terminator
let mut v = vec::with_capacity(self.len() * 2 + 1);
for &byte in self.iter() {
s.push_char(CHARS[byte >> 4]);
s.push_char(CHARS[byte & 0xf]);
v.push(CHARS[byte >> 4]);
v.push(CHARS[byte & 0xf]);
}
s
unsafe {
str::raw::from_bytes_owned(v)
}
}
}