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Optimize escape_ascii. #125340

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Optimize escape_ascii. #125340

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8b94af3
Optimize `escape_ascii`.
reitermarkus May 20, 2024
c9c3f91
Order `escape_ascii` by character frequency.
reitermarkus May 22, 2024
5606b02
Fix match ordering.
reitermarkus May 22, 2024
b161093
Further optimization.
reitermarkus Jun 1, 2024
798c652
Update escape.rs
reitermarkus Jun 1, 2024
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58 changes: 32 additions & 26 deletions library/core/src/escape.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -24,34 +24,40 @@ const fn backslash<const N: usize>(a: ascii::Char) -> ([ascii::Char; N], Range<u
const fn escape_ascii<const N: usize>(byte: u8) -> ([ascii::Char; N], Range<u8>) {
const { assert!(N >= 4) };

match byte {
b'\t' => backslash(ascii::Char::SmallT),
b'\r' => backslash(ascii::Char::SmallR),
b'\n' => backslash(ascii::Char::SmallN),
b'\\' => backslash(ascii::Char::ReverseSolidus),
b'\'' => backslash(ascii::Char::Apostrophe),
b'\"' => backslash(ascii::Char::QuotationMark),
byte => {
let mut output = [ascii::Char::Null; N];

if let Some(c) = byte.as_ascii()
&& !byte.is_ascii_control()
{
output[0] = c;
(output, 0..1)
} else {
let hi = HEX_DIGITS[(byte >> 4) as usize];
let lo = HEX_DIGITS[(byte & 0xf) as usize];

output[0] = ascii::Char::ReverseSolidus;
output[1] = ascii::Char::SmallX;
output[2] = hi;
output[3] = lo;

(output, 0..4)
let mut output = [ascii::Char::ReverseSolidus; N];
output[1] = ascii::Char::SmallX;
output[2] = HEX_DIGITS[(byte >> 4) as usize];
output[3] = HEX_DIGITS[(byte & 0b1111) as usize];

let len = if byte < 127 {
match byte {
c @ b'\"' | c @ b'\'' | c @ b'\\' => {
output[1] = c.as_ascii().unwrap();
2
}
c @ 0x20..=0x7e => {
output[0] = c.as_ascii().unwrap();
1
}
b'\n' => {
output[1] = ascii::Char::SmallN;
2
}
b'\r' => {
output[1] = ascii::Char::SmallR;
2
}
b'\t' => {
output[1] = ascii::Char::SmallT;
2
}
_ => 4,
}
}
} else {
4
};

(output, 0..len)
}

/// Escapes a character `\u{NNNN}` representation.
Expand Down