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core: optimise Debug impl for ascii::Char

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Rather than writing character at a time, optimise Debug implementation
for core::ascii::Char such that it writes the entire representation as
with a single write_str call.

With that, add tests for Display and Debug implementations.
This commit is contained in:
Michal Nazarewicz
2024-01-24 16:48:54 +01:00
parent 19ebdcedf1
commit 7d1de7f994
3 changed files with 42 additions and 19 deletions
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32
library/core/src/ascii/ascii_char.rs
View File

@@ -3,7 +3,7 @@
//! suggestions from rustc if you get anything slightly wrong in here, and overall
//! helps with clarity as we're also referring to `char` intentionally in here.
use crate::fmt::{self, Write};
use crate::fmt;
use crate::mem::transmute;
/// One of the 128 Unicode characters from U+0000 through U+007F,
@@ -583,9 +583,10 @@ impl fmt::Display for AsciiChar {
#[unstable(feature = "ascii_char", issue = "110998")]
impl fmt::Debug for AsciiChar {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
#[inline]
fn backslash(a: AsciiChar) -> ([AsciiChar; 4], u8) {
([AsciiChar::ReverseSolidus, a, AsciiChar::Null, AsciiChar::Null], 2)
use AsciiChar::{Apostrophe, Null, ReverseSolidus as Backslash};
fn backslash(a: AsciiChar) -> ([AsciiChar; 6], usize) {
([Apostrophe, Backslash, a, Apostrophe, Null, Null], 4)
}
let (buf, len) = match self {
@@ -595,24 +596,17 @@ impl fmt::Debug for AsciiChar {
AsciiChar::LineFeed => backslash(AsciiChar::SmallN),
AsciiChar::ReverseSolidus => backslash(AsciiChar::ReverseSolidus),
AsciiChar::Apostrophe => backslash(AsciiChar::Apostrophe),
_ => {
let byte = self.to_u8();
if !byte.is_ascii_control() {
([*self, AsciiChar::Null, AsciiChar::Null, AsciiChar::Null], 1)
} else {
const HEX_DIGITS: [AsciiChar; 16] = *b"0123456789abcdef".as_ascii().unwrap();
_ if self.to_u8().is_ascii_control() => {
const HEX_DIGITS: [AsciiChar; 16] = *b"0123456789abcdef".as_ascii().unwrap();
let hi = HEX_DIGITS[usize::from(byte >> 4)];
let lo = HEX_DIGITS[usize::from(byte & 0xf)];
([AsciiChar::ReverseSolidus, AsciiChar::SmallX, hi, lo], 4)
}
let byte = self.to_u8();
let hi = HEX_DIGITS[usize::from(byte >> 4)];
let lo = HEX_DIGITS[usize::from(byte & 0xf)];
([Apostrophe, Backslash, AsciiChar::SmallX, hi, lo, Apostrophe], 6)
}
_ => ([Apostrophe, *self, Apostrophe, Null, Null, Null], 3),
};
f.write_char('\'')?;
for byte in &buf[..len as usize] {
f.write_str(byte.as_str())?;
}
f.write_char('\'')
f.write_str(buf[..len].as_str())
}
}