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Diffstat (limited to '')
-rw-r--r-- | library/core/src/str/validations.rs | 274 |
1 files changed, 274 insertions, 0 deletions
diff --git a/library/core/src/str/validations.rs b/library/core/src/str/validations.rs new file mode 100644 index 000000000..04bc66523 --- /dev/null +++ b/library/core/src/str/validations.rs @@ -0,0 +1,274 @@ +//! Operations related to UTF-8 validation. + +use crate::mem; + +use super::Utf8Error; + +/// Returns the initial codepoint accumulator for the first byte. +/// The first byte is special, only want bottom 5 bits for width 2, 4 bits +/// for width 3, and 3 bits for width 4. +#[inline] +const fn utf8_first_byte(byte: u8, width: u32) -> u32 { + (byte & (0x7F >> width)) as u32 +} + +/// Returns the value of `ch` updated with continuation byte `byte`. +#[inline] +const fn utf8_acc_cont_byte(ch: u32, byte: u8) -> u32 { + (ch << 6) | (byte & CONT_MASK) as u32 +} + +/// Checks whether the byte is a UTF-8 continuation byte (i.e., starts with the +/// bits `10`). +#[inline] +pub(super) const fn utf8_is_cont_byte(byte: u8) -> bool { + (byte as i8) < -64 +} + +/// Reads the next code point out of a byte iterator (assuming a +/// UTF-8-like encoding). +/// +/// # Safety +/// +/// `bytes` must produce a valid UTF-8-like (UTF-8 or WTF-8) string +#[unstable(feature = "str_internals", issue = "none")] +#[inline] +pub unsafe fn next_code_point<'a, I: Iterator<Item = &'a u8>>(bytes: &mut I) -> Option<u32> { + // Decode UTF-8 + let x = *bytes.next()?; + if x < 128 { + return Some(x as u32); + } + + // Multibyte case follows + // Decode from a byte combination out of: [[[x y] z] w] + // NOTE: Performance is sensitive to the exact formulation here + let init = utf8_first_byte(x, 2); + // SAFETY: `bytes` produces an UTF-8-like string, + // so the iterator must produce a value here. + let y = unsafe { *bytes.next().unwrap_unchecked() }; + let mut ch = utf8_acc_cont_byte(init, y); + if x >= 0xE0 { + // [[x y z] w] case + // 5th bit in 0xE0 .. 0xEF is always clear, so `init` is still valid + // SAFETY: `bytes` produces an UTF-8-like string, + // so the iterator must produce a value here. + let z = unsafe { *bytes.next().unwrap_unchecked() }; + let y_z = utf8_acc_cont_byte((y & CONT_MASK) as u32, z); + ch = init << 12 | y_z; + if x >= 0xF0 { + // [x y z w] case + // use only the lower 3 bits of `init` + // SAFETY: `bytes` produces an UTF-8-like string, + // so the iterator must produce a value here. + let w = unsafe { *bytes.next().unwrap_unchecked() }; + ch = (init & 7) << 18 | utf8_acc_cont_byte(y_z, w); + } + } + + Some(ch) +} + +/// Reads the last code point out of a byte iterator (assuming a +/// UTF-8-like encoding). +/// +/// # Safety +/// +/// `bytes` must produce a valid UTF-8-like (UTF-8 or WTF-8) string +#[inline] +pub(super) unsafe fn next_code_point_reverse<'a, I>(bytes: &mut I) -> Option<u32> +where + I: DoubleEndedIterator<Item = &'a u8>, +{ + // Decode UTF-8 + let w = match *bytes.next_back()? { + next_byte if next_byte < 128 => return Some(next_byte as u32), + back_byte => back_byte, + }; + + // Multibyte case follows + // Decode from a byte combination out of: [x [y [z w]]] + let mut ch; + // SAFETY: `bytes` produces an UTF-8-like string, + // so the iterator must produce a value here. + let z = unsafe { *bytes.next_back().unwrap_unchecked() }; + ch = utf8_first_byte(z, 2); + if utf8_is_cont_byte(z) { + // SAFETY: `bytes` produces an UTF-8-like string, + // so the iterator must produce a value here. + let y = unsafe { *bytes.next_back().unwrap_unchecked() }; + ch = utf8_first_byte(y, 3); + if utf8_is_cont_byte(y) { + // SAFETY: `bytes` produces an UTF-8-like string, + // so the iterator must produce a value here. + let x = unsafe { *bytes.next_back().unwrap_unchecked() }; + ch = utf8_first_byte(x, 4); + ch = utf8_acc_cont_byte(ch, y); + } + ch = utf8_acc_cont_byte(ch, z); + } + ch = utf8_acc_cont_byte(ch, w); + + Some(ch) +} + +const NONASCII_MASK: usize = usize::repeat_u8(0x80); + +/// Returns `true` if any byte in the word `x` is nonascii (>= 128). +#[inline] +const fn contains_nonascii(x: usize) -> bool { + (x & NONASCII_MASK) != 0 +} + +/// Walks through `v` checking that it's a valid UTF-8 sequence, +/// returning `Ok(())` in that case, or, if it is invalid, `Err(err)`. +#[inline(always)] +#[rustc_const_unstable(feature = "str_internals", issue = "none")] +pub(super) const fn run_utf8_validation(v: &[u8]) -> Result<(), Utf8Error> { + let mut index = 0; + let len = v.len(); + + let usize_bytes = mem::size_of::<usize>(); + let ascii_block_size = 2 * usize_bytes; + let blocks_end = if len >= ascii_block_size { len - ascii_block_size + 1 } else { 0 }; + let align = v.as_ptr().align_offset(usize_bytes); + + while index < len { + let old_offset = index; + macro_rules! err { + ($error_len: expr) => { + return Err(Utf8Error { valid_up_to: old_offset, error_len: $error_len }) + }; + } + + macro_rules! next { + () => {{ + index += 1; + // we needed data, but there was none: error! + if index >= len { + err!(None) + } + v[index] + }}; + } + + let first = v[index]; + if first >= 128 { + let w = utf8_char_width(first); + // 2-byte encoding is for codepoints \u{0080} to \u{07ff} + // first C2 80 last DF BF + // 3-byte encoding is for codepoints \u{0800} to \u{ffff} + // first E0 A0 80 last EF BF BF + // excluding surrogates codepoints \u{d800} to \u{dfff} + // ED A0 80 to ED BF BF + // 4-byte encoding is for codepoints \u{1000}0 to \u{10ff}ff + // first F0 90 80 80 last F4 8F BF BF + // + // Use the UTF-8 syntax from the RFC + // + // https://tools.ietf.org/html/rfc3629 + // UTF8-1 = %x00-7F + // UTF8-2 = %xC2-DF UTF8-tail + // UTF8-3 = %xE0 %xA0-BF UTF8-tail / %xE1-EC 2( UTF8-tail ) / + // %xED %x80-9F UTF8-tail / %xEE-EF 2( UTF8-tail ) + // UTF8-4 = %xF0 %x90-BF 2( UTF8-tail ) / %xF1-F3 3( UTF8-tail ) / + // %xF4 %x80-8F 2( UTF8-tail ) + match w { + 2 => { + if next!() as i8 >= -64 { + err!(Some(1)) + } + } + 3 => { + match (first, next!()) { + (0xE0, 0xA0..=0xBF) + | (0xE1..=0xEC, 0x80..=0xBF) + | (0xED, 0x80..=0x9F) + | (0xEE..=0xEF, 0x80..=0xBF) => {} + _ => err!(Some(1)), + } + if next!() as i8 >= -64 { + err!(Some(2)) + } + } + 4 => { + match (first, next!()) { + (0xF0, 0x90..=0xBF) | (0xF1..=0xF3, 0x80..=0xBF) | (0xF4, 0x80..=0x8F) => {} + _ => err!(Some(1)), + } + if next!() as i8 >= -64 { + err!(Some(2)) + } + if next!() as i8 >= -64 { + err!(Some(3)) + } + } + _ => err!(Some(1)), + } + index += 1; + } else { + // Ascii case, try to skip forward quickly. + // When the pointer is aligned, read 2 words of data per iteration + // until we find a word containing a non-ascii byte. + if align != usize::MAX && align.wrapping_sub(index) % usize_bytes == 0 { + let ptr = v.as_ptr(); + while index < blocks_end { + // SAFETY: since `align - index` and `ascii_block_size` are + // multiples of `usize_bytes`, `block = ptr.add(index)` is + // always aligned with a `usize` so it's safe to dereference + // both `block` and `block.offset(1)`. + unsafe { + let block = ptr.add(index) as *const usize; + // break if there is a nonascii byte + let zu = contains_nonascii(*block); + let zv = contains_nonascii(*block.offset(1)); + if zu || zv { + break; + } + } + index += ascii_block_size; + } + // step from the point where the wordwise loop stopped + while index < len && v[index] < 128 { + index += 1; + } + } else { + index += 1; + } + } + } + + Ok(()) +} + +// https://tools.ietf.org/html/rfc3629 +const UTF8_CHAR_WIDTH: &[u8; 256] = &[ + // 1 2 3 4 5 6 7 8 9 A B C D E F + 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 0 + 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 1 + 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 2 + 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 3 + 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 4 + 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 5 + 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 6 + 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 7 + 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // 8 + 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // 9 + 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // A + 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // B + 0, 0, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, // C + 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, // D + 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, // E + 4, 4, 4, 4, 4, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // F +]; + +/// Given a first byte, determines how many bytes are in this UTF-8 character. +#[unstable(feature = "str_internals", issue = "none")] +#[must_use] +#[inline] +pub const fn utf8_char_width(b: u8) -> usize { + UTF8_CHAR_WIDTH[b as usize] as usize +} + +/// Mask of the value bits of a continuation byte. +const CONT_MASK: u8 = 0b0011_1111; |