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Diffstat (limited to 'library/core/src/escape.rs')
-rw-r--r-- | library/core/src/escape.rs | 112 |
1 files changed, 112 insertions, 0 deletions
diff --git a/library/core/src/escape.rs b/library/core/src/escape.rs new file mode 100644 index 000000000..3d471419b --- /dev/null +++ b/library/core/src/escape.rs @@ -0,0 +1,112 @@ +//! Helper code for character escaping. + +use crate::ascii; +use crate::num::NonZeroUsize; +use crate::ops::Range; + +const HEX_DIGITS: [ascii::Char; 16] = *b"0123456789abcdef".as_ascii().unwrap(); + +/// Escapes a byte into provided buffer; returns length of escaped +/// representation. +pub(crate) fn escape_ascii_into(output: &mut [ascii::Char; 4], byte: u8) -> Range<u8> { + #[inline] + fn backslash(a: ascii::Char) -> ([ascii::Char; 4], u8) { + ([ascii::Char::ReverseSolidus, a, ascii::Char::Null, ascii::Char::Null], 2) + } + + let (data, len) = 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), + _ => if let Some(a) = byte.as_ascii() && !byte.is_ascii_control() { + ([a, ascii::Char::Null, ascii::Char::Null, ascii::Char::Null], 1) + } else { + let hi = HEX_DIGITS[usize::from(byte >> 4)]; + let lo = HEX_DIGITS[usize::from(byte & 0xf)]; + ([ascii::Char::ReverseSolidus, ascii::Char::SmallX, hi, lo], 4) + } + }; + *output = data; + 0..len +} + +/// Escapes a character into provided buffer using `\u{NNNN}` representation. +pub(crate) fn escape_unicode_into(output: &mut [ascii::Char; 10], ch: char) -> Range<u8> { + output[9] = ascii::Char::RightCurlyBracket; + + let ch = ch as u32; + output[3] = HEX_DIGITS[((ch >> 20) & 15) as usize]; + output[4] = HEX_DIGITS[((ch >> 16) & 15) as usize]; + output[5] = HEX_DIGITS[((ch >> 12) & 15) as usize]; + output[6] = HEX_DIGITS[((ch >> 8) & 15) as usize]; + output[7] = HEX_DIGITS[((ch >> 4) & 15) as usize]; + output[8] = HEX_DIGITS[((ch >> 0) & 15) as usize]; + + // or-ing 1 ensures that for ch==0 the code computes that one digit should + // be printed. + let start = (ch | 1).leading_zeros() as usize / 4 - 2; + const UNICODE_ESCAPE_PREFIX: &[ascii::Char; 3] = b"\\u{".as_ascii().unwrap(); + output[start..][..3].copy_from_slice(UNICODE_ESCAPE_PREFIX); + + (start as u8)..10 +} + +/// An iterator over an fixed-size array. +/// +/// This is essentially equivalent to array’s IntoIter except that indexes are +/// limited to u8 to reduce size of the structure. +#[derive(Clone, Debug)] +pub(crate) struct EscapeIterInner<const N: usize> { + // The element type ensures this is always ASCII, and thus also valid UTF-8. + pub(crate) data: [ascii::Char; N], + + // Invariant: alive.start <= alive.end <= N. + pub(crate) alive: Range<u8>, +} + +impl<const N: usize> EscapeIterInner<N> { + pub fn new(data: [ascii::Char; N], alive: Range<u8>) -> Self { + const { assert!(N < 256) }; + debug_assert!(alive.start <= alive.end && usize::from(alive.end) <= N, "{alive:?}"); + Self { data, alive } + } + + pub fn from_array<const M: usize>(array: [ascii::Char; M]) -> Self { + const { assert!(M <= N) }; + + let mut data = [ascii::Char::Null; N]; + data[..M].copy_from_slice(&array); + Self::new(data, 0..M as u8) + } + + pub fn as_ascii(&self) -> &[ascii::Char] { + &self.data[usize::from(self.alive.start)..usize::from(self.alive.end)] + } + + pub fn as_str(&self) -> &str { + self.as_ascii().as_str() + } + + pub fn len(&self) -> usize { + usize::from(self.alive.end - self.alive.start) + } + + pub fn next(&mut self) -> Option<u8> { + self.alive.next().map(|i| self.data[usize::from(i)].as_u8()) + } + + pub fn next_back(&mut self) -> Option<u8> { + self.alive.next_back().map(|i| self.data[usize::from(i)].as_u8()) + } + + pub fn advance_by(&mut self, n: usize) -> Result<(), NonZeroUsize> { + self.alive.advance_by(n) + } + + pub fn advance_back_by(&mut self, n: usize) -> Result<(), NonZeroUsize> { + self.alive.advance_back_by(n) + } +} |