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optimization continuation byte validation of strings containing multibyte chars

Browse Source 
```
old, -O2, x86-64
test str::str_validate_emoji                                    ... bench:       4,606 ns/iter (+/- 64)

new, -O2, x86-64
test str::str_validate_emoji                                    ... bench:       3,837 ns/iter (+/- 60)
```
This commit is contained in:
The8472 2021-09-11 00:09:49 +02:00
parent b6278664af
commit 66195d8bc4
1 changed files with 4 additions and 6 deletions
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10
library/core/src/str/validations.rs
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@ -163,7 +163,7 @@ pub(super) fn run_utf8_validation(v: &[u8]) -> Result<(), Utf8Error> {
// %xF4 %x80-8F 2( UTF8-tail )
match w {
2 => {
if next!() & !CONT_MASK != TAG_CONT_U8 {
if !utf8_is_cont_byte(next!()) {
err!(Some(1))
}
}
@ -175,7 +175,7 @@ pub(super) fn run_utf8_validation(v: &[u8]) -> Result<(), Utf8Error> {
| (0xEE..=0xEF, 0x80..=0xBF) => {}
_ => err!(Some(1)),
}
if next!() & !CONT_MASK != TAG_CONT_U8 {
if !utf8_is_cont_byte(next!()) {
err!(Some(2))
}
}
@ -184,10 +184,10 @@ pub(super) fn run_utf8_validation(v: &[u8]) -> Result<(), Utf8Error> {
(0xF0, 0x90..=0xBF) | (0xF1..=0xF3, 0x80..=0xBF) | (0xF4, 0x80..=0x8F) => {}
_ => err!(Some(1)),
}
if next!() & !CONT_MASK != TAG_CONT_U8 {
if !utf8_is_cont_byte(next!()) {
err!(Some(2))
}
if next!() & !CONT_MASK != TAG_CONT_U8 {
if !utf8_is_cont_byte(next!()) {
err!(Some(3))
}
}
@ -258,8 +258,6 @@ pub fn utf8_char_width(b: u8) -> usize {
/// Mask of the value bits of a continuation byte.
const CONT_MASK: u8 = 0b0011_1111;
/// Value of the tag bits (tag mask is !CONT_MASK) of a continuation byte.
const TAG_CONT_U8: u8 = 0b1000_0000;
// truncate `&str` to length at most equal to `max`
// return `true` if it were truncated, and the new str.