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String::from_utf16 using a pre-allocated push loop vs. collect()
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#![feature(test)] | |
extern crate test; | |
use test::{Bencher, black_box}; | |
use std::string::FromUtf16Error; | |
use std::char::decode_utf16; | |
const S15: &[u16]= &[0xd800, 0xdf45, 0xd800, 0xdf3f, 0xd800, 0xdf3b, 0xd800, 0xdf46, 0xd800, | |
0xdf39, 0xd800, 0xdf3b, 0xd800, 0xdf30, 0x000a]; | |
const S41: &[u16] = &[0xd801, 0xdc8b, 0xd801, 0xdc98, 0xd801, 0xdc88, 0xd801, 0xdc91, 0xd801, | |
0xdc9b, 0xd801, 0xdc92, 0x0020, 0xd801, 0xdc95, 0xd801, 0xdc93, 0x0020, | |
0xd801, 0xdc88, 0xd801, 0xdc9a, 0xd801, 0xdc8d, 0x0020, 0xd801, 0xdc8f, | |
0xd801, 0xdc9c, 0xd801, 0xdc92, 0xd801, 0xdc96, 0xd801, 0xdc86, 0x0020, | |
0xd801, 0xdc95, 0xd801, 0xdc86, 0x000a]; | |
fn old(str_u16: &[u16]) -> Result<String, FromUtf16Error> { | |
String::from_utf16(str_u16) | |
} | |
fn new(str_u16: &[u16]) -> Result<String, ()> { | |
let mut ret = String::with_capacity(str_u16.len()); | |
for c in decode_utf16(str_u16.iter().cloned()) { | |
if let Ok(c) = c { | |
ret.push(c); | |
} else { | |
return Err(()); | |
} | |
} | |
Ok(ret) | |
} | |
#[bench] | |
fn bench_old(b: &mut Bencher) { | |
b.iter(|| old(black_box(S41))) | |
} | |
#[bench] | |
fn bench_new(b: &mut Bencher) { | |
b.iter(|| new(black_box(S41))) | |
} |
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