// Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT // file at the top-level directory of this distribution and at // http://rust-lang.org/COPYRIGHT. // // Licensed under the Apache License, Version 2.0 or the MIT license // , at your // option. This file may not be copied, modified, or distributed // except according to those terms. //! Character manipulation. //! //! For more details, see ::std_unicode::char (a.k.a. std::char) #![allow(non_snake_case)] #![stable(feature = "core_char", since = "1.2.0")] use char_private::is_printable; use convert::TryFrom; use fmt::{self, Write}; use slice; use str::{from_utf8_unchecked_mut, FromStr}; use iter::FusedIterator; use mem::transmute; // UTF-8 ranges and tags for encoding characters const TAG_CONT: u8 = 0b1000_0000; const TAG_TWO_B: u8 = 0b1100_0000; const TAG_THREE_B: u8 = 0b1110_0000; const TAG_FOUR_B: u8 = 0b1111_0000; const MAX_ONE_B: u32 = 0x80; const MAX_TWO_B: u32 = 0x800; const MAX_THREE_B: u32 = 0x10000; /* Lu Uppercase_Letter an uppercase letter Ll Lowercase_Letter a lowercase letter Lt Titlecase_Letter a digraphic character, with first part uppercase Lm Modifier_Letter a modifier letter Lo Other_Letter other letters, including syllables and ideographs Mn Nonspacing_Mark a nonspacing combining mark (zero advance width) Mc Spacing_Mark a spacing combining mark (positive advance width) Me Enclosing_Mark an enclosing combining mark Nd Decimal_Number a decimal digit Nl Letter_Number a letterlike numeric character No Other_Number a numeric character of other type Pc Connector_Punctuation a connecting punctuation mark, like a tie Pd Dash_Punctuation a dash or hyphen punctuation mark Ps Open_Punctuation an opening punctuation mark (of a pair) Pe Close_Punctuation a closing punctuation mark (of a pair) Pi Initial_Punctuation an initial quotation mark Pf Final_Punctuation a final quotation mark Po Other_Punctuation a punctuation mark of other type Sm Math_Symbol a symbol of primarily mathematical use Sc Currency_Symbol a currency sign Sk Modifier_Symbol a non-letterlike modifier symbol So Other_Symbol a symbol of other type Zs Space_Separator a space character (of various non-zero widths) Zl Line_Separator U+2028 LINE SEPARATOR only Zp Paragraph_Separator U+2029 PARAGRAPH SEPARATOR only Cc Control a C0 or C1 control code Cf Format a format control character Cs Surrogate a surrogate code point Co Private_Use a private-use character Cn Unassigned a reserved unassigned code point or a noncharacter */ /// The highest valid code point a `char` can have. /// /// A [`char`] is a [Unicode Scalar Value], which means that it is a [Code /// Point], but only ones within a certain range. `MAX` is the highest valid /// code point that's a valid [Unicode Scalar Value]. /// /// [`char`]: ../../std/primitive.char.html /// [Unicode Scalar Value]: http://www.unicode.org/glossary/#unicode_scalar_value /// [Code Point]: http://www.unicode.org/glossary/#code_point #[stable(feature = "rust1", since = "1.0.0")] pub const MAX: char = '\u{10ffff}'; /// Converts a `u32` to a `char`. /// /// Note that all [`char`]s are valid [`u32`]s, and can be cast to one with /// [`as`]: /// /// ``` /// let c = '💯'; /// let i = c as u32; /// /// assert_eq!(128175, i); /// ``` /// /// However, the reverse is not true: not all valid [`u32`]s are valid /// [`char`]s. `from_u32()` will return `None` if the input is not a valid value /// for a [`char`]. /// /// [`char`]: ../../std/primitive.char.html /// [`u32`]: ../../std/primitive.u32.html /// [`as`]: ../../book/first-edition/casting-between-types.html#as /// /// For an unsafe version of this function which ignores these checks, see /// [`from_u32_unchecked`]. /// /// [`from_u32_unchecked`]: fn.from_u32_unchecked.html /// /// # Examples /// /// Basic usage: /// /// ``` /// use std::char; /// /// let c = char::from_u32(0x2764); /// /// assert_eq!(Some('❤'), c); /// ``` /// /// Returning `None` when the input is not a valid [`char`]: /// /// ``` /// use std::char; /// /// let c = char::from_u32(0x110000); /// /// assert_eq!(None, c); /// ``` #[inline] #[stable(feature = "rust1", since = "1.0.0")] pub fn from_u32(i: u32) -> Option { char::try_from(i).ok() } /// Converts a `u32` to a `char`, ignoring validity. /// /// Note that all [`char`]s are valid [`u32`]s, and can be cast to one with /// [`as`]: /// /// ``` /// let c = '💯'; /// let i = c as u32; /// /// assert_eq!(128175, i); /// ``` /// /// However, the reverse is not true: not all valid [`u32`]s are valid /// [`char`]s. `from_u32_unchecked()` will ignore this, and blindly cast to /// [`char`], possibly creating an invalid one. /// /// [`char`]: ../../std/primitive.char.html /// [`u32`]: ../../std/primitive.u32.html /// [`as`]: ../../book/first-edition/casting-between-types.html#as /// /// # Safety /// /// This function is unsafe, as it may construct invalid `char` values. /// /// For a safe version of this function, see the [`from_u32`] function. /// /// [`from_u32`]: fn.from_u32.html /// /// # Examples /// /// Basic usage: /// /// ``` /// use std::char; /// /// let c = unsafe { char::from_u32_unchecked(0x2764) }; /// /// assert_eq!('❤', c); /// ``` #[inline] #[stable(feature = "char_from_unchecked", since = "1.5.0")] pub unsafe fn from_u32_unchecked(i: u32) -> char { transmute(i) } #[stable(feature = "char_convert", since = "1.13.0")] impl From for u32 { #[inline] fn from(c: char) -> Self { c as u32 } } /// Maps a byte in 0x00...0xFF to a `char` whose code point has the same value, in U+0000 to U+00FF. /// /// Unicode is designed such that this effectively decodes bytes /// with the character encoding that IANA calls ISO-8859-1. /// This encoding is compatible with ASCII. /// /// Note that this is different from ISO/IEC 8859-1 a.k.a. ISO 8859-1 (with one less hyphen), /// which leaves some "blanks", byte values that are not assigned to any character. /// ISO-8859-1 (the IANA one) assigns them to the C0 and C1 control codes. /// /// Note that this is *also* different from Windows-1252 a.k.a. code page 1252, /// which is a superset ISO/IEC 8859-1 that assigns some (not all!) blanks /// to punctuation and various Latin characters. /// /// To confuse things further, [on the Web](https://encoding.spec.whatwg.org/) /// `ascii`, `iso-8859-1`, and `windows-1252` are all aliases /// for a superset of Windows-1252 that fills the remaining blanks with corresponding /// C0 and C1 control codes. #[stable(feature = "char_convert", since = "1.13.0")] impl From for char { #[inline] fn from(i: u8) -> Self { i as char } } /// An error which can be returned when parsing a char. #[stable(feature = "char_from_str", since = "1.20.0")] #[derive(Clone, Debug, PartialEq, Eq)] pub struct ParseCharError { kind: CharErrorKind, } impl ParseCharError { #[unstable(feature = "char_error_internals", reason = "this method should not be available publicly", issue = "0")] #[doc(hidden)] pub fn __description(&self) -> &str { match self.kind { CharErrorKind::EmptyString => { "cannot parse char from empty string" }, CharErrorKind::TooManyChars => "too many characters in string" } } } #[derive(Copy, Clone, Debug, PartialEq, Eq)] enum CharErrorKind { EmptyString, TooManyChars, } #[stable(feature = "char_from_str", since = "1.20.0")] impl fmt::Display for ParseCharError { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { self.__description().fmt(f) } } #[stable(feature = "char_from_str", since = "1.20.0")] impl FromStr for char { type Err = ParseCharError; #[inline] fn from_str(s: &str) -> Result { let mut chars = s.chars(); match (chars.next(), chars.next()) { (None, _) => { Err(ParseCharError { kind: CharErrorKind::EmptyString }) }, (Some(c), None) => Ok(c), _ => { Err(ParseCharError { kind: CharErrorKind::TooManyChars }) } } } } #[unstable(feature = "try_from", issue = "33417")] impl TryFrom for char { type Error = CharTryFromError; #[inline] fn try_from(i: u32) -> Result { if (i > MAX as u32) || (i >= 0xD800 && i <= 0xDFFF) { Err(CharTryFromError(())) } else { Ok(unsafe { from_u32_unchecked(i) }) } } } /// The error type returned when a conversion from u32 to char fails. #[unstable(feature = "try_from", issue = "33417")] #[derive(Copy, Clone, Debug, PartialEq, Eq)] pub struct CharTryFromError(()); #[unstable(feature = "try_from", issue = "33417")] impl fmt::Display for CharTryFromError { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { "converted integer out of range for `char`".fmt(f) } } /// Converts a digit in the given radix to a `char`. /// /// A 'radix' here is sometimes also called a 'base'. A radix of two /// indicates a binary number, a radix of ten, decimal, and a radix of /// sixteen, hexadecimal, to give some common values. Arbitrary /// radices are supported. /// /// `from_digit()` will return `None` if the input is not a digit in /// the given radix. /// /// # Panics /// /// Panics if given a radix larger than 36. /// /// # Examples /// /// Basic usage: /// /// ``` /// use std::char; /// /// let c = char::from_digit(4, 10); /// /// assert_eq!(Some('4'), c); /// /// // Decimal 11 is a single digit in base 16 /// let c = char::from_digit(11, 16); /// /// assert_eq!(Some('b'), c); /// ``` /// /// Returning `None` when the input is not a digit: /// /// ``` /// use std::char; /// /// let c = char::from_digit(20, 10); /// /// assert_eq!(None, c); /// ``` /// /// Passing a large radix, causing a panic: /// /// ``` /// use std::thread; /// use std::char; /// /// let result = thread::spawn(|| { /// // this panics /// let c = char::from_digit(1, 37); /// }).join(); /// /// assert!(result.is_err()); /// ``` #[inline] #[stable(feature = "rust1", since = "1.0.0")] pub fn from_digit(num: u32, radix: u32) -> Option { if radix > 36 { panic!("from_digit: radix is too high (maximum 36)"); } if num < radix { let num = num as u8; if num < 10 { Some((b'0' + num) as char) } else { Some((b'a' + num - 10) as char) } } else { None } } // NB: the stabilization and documentation for this trait is in // unicode/char.rs, not here #[allow(missing_docs)] // docs in libunicode/u_char.rs #[doc(hidden)] #[unstable(feature = "core_char_ext", reason = "the stable interface is `impl char` in later crate", issue = "32110")] pub trait CharExt { #[stable(feature = "core", since = "1.6.0")] fn is_digit(self, radix: u32) -> bool; #[stable(feature = "core", since = "1.6.0")] fn to_digit(self, radix: u32) -> Option; #[stable(feature = "core", since = "1.6.0")] fn escape_unicode(self) -> EscapeUnicode; #[stable(feature = "core", since = "1.6.0")] fn escape_default(self) -> EscapeDefault; #[stable(feature = "char_escape_debug", since = "1.20.0")] fn escape_debug(self) -> EscapeDebug; #[stable(feature = "core", since = "1.6.0")] fn len_utf8(self) -> usize; #[stable(feature = "core", since = "1.6.0")] fn len_utf16(self) -> usize; #[stable(feature = "unicode_encode_char", since = "1.15.0")] fn encode_utf8(self, dst: &mut [u8]) -> &mut str; #[stable(feature = "unicode_encode_char", since = "1.15.0")] fn encode_utf16(self, dst: &mut [u16]) -> &mut [u16]; } #[stable(feature = "core", since = "1.6.0")] impl CharExt for char { #[inline] fn is_digit(self, radix: u32) -> bool { self.to_digit(radix).is_some() } #[inline] fn to_digit(self, radix: u32) -> Option { if radix > 36 { panic!("to_digit: radix is too high (maximum 36)"); } let val = match self { '0' ... '9' => self as u32 - '0' as u32, 'a' ... 'z' => self as u32 - 'a' as u32 + 10, 'A' ... 'Z' => self as u32 - 'A' as u32 + 10, _ => return None, }; if val < radix { Some(val) } else { None } } #[inline] fn escape_unicode(self) -> EscapeUnicode { let c = self as u32; // or-ing 1 ensures that for c==0 the code computes that one // digit should be printed and (which is the same) avoids the // (31 - 32) underflow let msb = 31 - (c | 1).leading_zeros(); // the index of the most significant hex digit let ms_hex_digit = msb / 4; EscapeUnicode { c: self, state: EscapeUnicodeState::Backslash, hex_digit_idx: ms_hex_digit as usize, } } #[inline] fn escape_default(self) -> EscapeDefault { let init_state = match self { '\t' => EscapeDefaultState::Backslash('t'), '\r' => EscapeDefaultState::Backslash('r'), '\n' => EscapeDefaultState::Backslash('n'), '\\' | '\'' | '"' => EscapeDefaultState::Backslash(self), '\x20' ... '\x7e' => EscapeDefaultState::Char(self), _ => EscapeDefaultState::Unicode(self.escape_unicode()) }; EscapeDefault { state: init_state } } #[inline] fn escape_debug(self) -> EscapeDebug { let init_state = match self { '\t' => EscapeDefaultState::Backslash('t'), '\r' => EscapeDefaultState::Backslash('r'), '\n' => EscapeDefaultState::Backslash('n'), '\\' | '\'' | '"' => EscapeDefaultState::Backslash(self), c if is_printable(c) => EscapeDefaultState::Char(c), c => EscapeDefaultState::Unicode(c.escape_unicode()), }; EscapeDebug(EscapeDefault { state: init_state }) } #[inline] fn len_utf8(self) -> usize { let code = self as u32; if code < MAX_ONE_B { 1 } else if code < MAX_TWO_B { 2 } else if code < MAX_THREE_B { 3 } else { 4 } } #[inline] fn len_utf16(self) -> usize { let ch = self as u32; if (ch & 0xFFFF) == ch { 1 } else { 2 } } #[inline] fn encode_utf8(self, dst: &mut [u8]) -> &mut str { let code = self as u32; unsafe { let len = if code < MAX_ONE_B && !dst.is_empty() { *dst.get_unchecked_mut(0) = code as u8; 1 } else if code < MAX_TWO_B && dst.len() >= 2 { *dst.get_unchecked_mut(0) = (code >> 6 & 0x1F) as u8 | TAG_TWO_B; *dst.get_unchecked_mut(1) = (code & 0x3F) as u8 | TAG_CONT; 2 } else if code < MAX_THREE_B && dst.len() >= 3 { *dst.get_unchecked_mut(0) = (code >> 12 & 0x0F) as u8 | TAG_THREE_B; *dst.get_unchecked_mut(1) = (code >> 6 & 0x3F) as u8 | TAG_CONT; *dst.get_unchecked_mut(2) = (code & 0x3F) as u8 | TAG_CONT; 3 } else if dst.len() >= 4 { *dst.get_unchecked_mut(0) = (code >> 18 & 0x07) as u8 | TAG_FOUR_B; *dst.get_unchecked_mut(1) = (code >> 12 & 0x3F) as u8 | TAG_CONT; *dst.get_unchecked_mut(2) = (code >> 6 & 0x3F) as u8 | TAG_CONT; *dst.get_unchecked_mut(3) = (code & 0x3F) as u8 | TAG_CONT; 4 } else { panic!("encode_utf8: need {} bytes to encode U+{:X}, but the buffer has {}", from_u32_unchecked(code).len_utf8(), code, dst.len()) }; from_utf8_unchecked_mut(dst.get_unchecked_mut(..len)) } } #[inline] fn encode_utf16(self, dst: &mut [u16]) -> &mut [u16] { let mut code = self as u32; unsafe { if (code & 0xFFFF) == code && !dst.is_empty() { // The BMP falls through (assuming non-surrogate, as it should) *dst.get_unchecked_mut(0) = code as u16; slice::from_raw_parts_mut(dst.as_mut_ptr(), 1) } else if dst.len() >= 2 { // Supplementary planes break into surrogates. code -= 0x1_0000; *dst.get_unchecked_mut(0) = 0xD800 | ((code >> 10) as u16); *dst.get_unchecked_mut(1) = 0xDC00 | ((code as u16) & 0x3FF); slice::from_raw_parts_mut(dst.as_mut_ptr(), 2) } else { panic!("encode_utf16: need {} units to encode U+{:X}, but the buffer has {}", from_u32_unchecked(code).len_utf16(), code, dst.len()) } } } } /// Returns an iterator that yields the hexadecimal Unicode escape of a /// character, as `char`s. /// /// This `struct` is created by the [`escape_unicode`] method on [`char`]. See /// its documentation for more. /// /// [`escape_unicode`]: ../../std/primitive.char.html#method.escape_unicode /// [`char`]: ../../std/primitive.char.html #[derive(Clone, Debug)] #[stable(feature = "rust1", since = "1.0.0")] pub struct EscapeUnicode { c: char, state: EscapeUnicodeState, // The index of the next hex digit to be printed (0 if none), // i.e. the number of remaining hex digits to be printed; // increasing from the least significant digit: 0x543210 hex_digit_idx: usize, } // The enum values are ordered so that their representation is the // same as the remaining length (besides the hexadecimal digits). This // likely makes `len()` a single load from memory) and inline-worth. #[derive(Clone, Debug)] enum EscapeUnicodeState { Done, RightBrace, Value, LeftBrace, Type, Backslash, } #[stable(feature = "rust1", since = "1.0.0")] impl Iterator for EscapeUnicode { type Item = char; fn next(&mut self) -> Option { match self.state { EscapeUnicodeState::Backslash => { self.state = EscapeUnicodeState::Type; Some('\\') } EscapeUnicodeState::Type => { self.state = EscapeUnicodeState::LeftBrace; Some('u') } EscapeUnicodeState::LeftBrace => { self.state = EscapeUnicodeState::Value; Some('{') } EscapeUnicodeState::Value => { let hex_digit = ((self.c as u32) >> (self.hex_digit_idx * 4)) & 0xf; let c = from_digit(hex_digit, 16).unwrap(); if self.hex_digit_idx == 0 { self.state = EscapeUnicodeState::RightBrace; } else { self.hex_digit_idx -= 1; } Some(c) } EscapeUnicodeState::RightBrace => { self.state = EscapeUnicodeState::Done; Some('}') } EscapeUnicodeState::Done => None, } } #[inline] fn size_hint(&self) -> (usize, Option) { let n = self.len(); (n, Some(n)) } #[inline] fn count(self) -> usize { self.len() } fn last(self) -> Option { match self.state { EscapeUnicodeState::Done => None, EscapeUnicodeState::RightBrace | EscapeUnicodeState::Value | EscapeUnicodeState::LeftBrace | EscapeUnicodeState::Type | EscapeUnicodeState::Backslash => Some('}'), } } } #[stable(feature = "exact_size_escape", since = "1.11.0")] impl ExactSizeIterator for EscapeUnicode { #[inline] fn len(&self) -> usize { // The match is a single memory access with no branching self.hex_digit_idx + match self.state { EscapeUnicodeState::Done => 0, EscapeUnicodeState::RightBrace => 1, EscapeUnicodeState::Value => 2, EscapeUnicodeState::LeftBrace => 3, EscapeUnicodeState::Type => 4, EscapeUnicodeState::Backslash => 5, } } } #[stable(feature = "fused", since = "1.26.0")] impl FusedIterator for EscapeUnicode {} #[stable(feature = "char_struct_display", since = "1.16.0")] impl fmt::Display for EscapeUnicode { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { for c in self.clone() { f.write_char(c)?; } Ok(()) } } /// An iterator that yields the literal escape code of a `char`. /// /// This `struct` is created by the [`escape_default`] method on [`char`]. See /// its documentation for more. /// /// [`escape_default`]: ../../std/primitive.char.html#method.escape_default /// [`char`]: ../../std/primitive.char.html #[derive(Clone, Debug)] #[stable(feature = "rust1", since = "1.0.0")] pub struct EscapeDefault { state: EscapeDefaultState } #[derive(Clone, Debug)] enum EscapeDefaultState { Done, Char(char), Backslash(char), Unicode(EscapeUnicode), } #[stable(feature = "rust1", since = "1.0.0")] impl Iterator for EscapeDefault { type Item = char; fn next(&mut self) -> Option { match self.state { EscapeDefaultState::Backslash(c) => { self.state = EscapeDefaultState::Char(c); Some('\\') } EscapeDefaultState::Char(c) => { self.state = EscapeDefaultState::Done; Some(c) } EscapeDefaultState::Done => None, EscapeDefaultState::Unicode(ref mut iter) => iter.next(), } } #[inline] fn size_hint(&self) -> (usize, Option) { let n = self.len(); (n, Some(n)) } #[inline] fn count(self) -> usize { self.len() } fn nth(&mut self, n: usize) -> Option { match self.state { EscapeDefaultState::Backslash(c) if n == 0 => { self.state = EscapeDefaultState::Char(c); Some('\\') }, EscapeDefaultState::Backslash(c) if n == 1 => { self.state = EscapeDefaultState::Done; Some(c) }, EscapeDefaultState::Backslash(_) => { self.state = EscapeDefaultState::Done; None }, EscapeDefaultState::Char(c) => { self.state = EscapeDefaultState::Done; if n == 0 { Some(c) } else { None } }, EscapeDefaultState::Done => return None, EscapeDefaultState::Unicode(ref mut i) => return i.nth(n), } } fn last(self) -> Option { match self.state { EscapeDefaultState::Unicode(iter) => iter.last(), EscapeDefaultState::Done => None, EscapeDefaultState::Backslash(c) | EscapeDefaultState::Char(c) => Some(c), } } } #[stable(feature = "exact_size_escape", since = "1.11.0")] impl ExactSizeIterator for EscapeDefault { fn len(&self) -> usize { match self.state { EscapeDefaultState::Done => 0, EscapeDefaultState::Char(_) => 1, EscapeDefaultState::Backslash(_) => 2, EscapeDefaultState::Unicode(ref iter) => iter.len(), } } } #[stable(feature = "fused", since = "1.26.0")] impl FusedIterator for EscapeDefault {} #[stable(feature = "char_struct_display", since = "1.16.0")] impl fmt::Display for EscapeDefault { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { for c in self.clone() { f.write_char(c)?; } Ok(()) } } /// An iterator that yields the literal escape code of a `char`. /// /// This `struct` is created by the [`escape_debug`] method on [`char`]. See its /// documentation for more. /// /// [`escape_debug`]: ../../std/primitive.char.html#method.escape_debug /// [`char`]: ../../std/primitive.char.html #[stable(feature = "char_escape_debug", since = "1.20.0")] #[derive(Clone, Debug)] pub struct EscapeDebug(EscapeDefault); #[stable(feature = "char_escape_debug", since = "1.20.0")] impl Iterator for EscapeDebug { type Item = char; fn next(&mut self) -> Option { self.0.next() } fn size_hint(&self) -> (usize, Option) { self.0.size_hint() } } #[stable(feature = "char_escape_debug", since = "1.20.0")] impl ExactSizeIterator for EscapeDebug { } #[stable(feature = "fused", since = "1.26.0")] impl FusedIterator for EscapeDebug {} #[stable(feature = "char_escape_debug", since = "1.20.0")] impl fmt::Display for EscapeDebug { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { fmt::Display::fmt(&self.0, f) } } /// An iterator over an iterator of bytes of the characters the bytes represent /// as UTF-8 #[unstable(feature = "decode_utf8", issue = "33906")] #[derive(Clone, Debug)] pub struct DecodeUtf8>(::iter::Peekable); /// Decodes an `Iterator` of bytes as UTF-8. #[unstable(feature = "decode_utf8", issue = "33906")] #[inline] pub fn decode_utf8>(i: I) -> DecodeUtf8 { DecodeUtf8(i.into_iter().peekable()) } /// `::next` returns this for an invalid input sequence. #[unstable(feature = "decode_utf8", issue = "33906")] #[derive(PartialEq, Eq, Debug)] pub struct InvalidSequence(()); #[unstable(feature = "decode_utf8", issue = "33906")] impl> Iterator for DecodeUtf8 { type Item = Result; #[inline] fn next(&mut self) -> Option> { self.0.next().map(|first_byte| { // Emit InvalidSequence according to // Unicode §5.22 Best Practice for U+FFFD Substitution // http://www.unicode.org/versions/Unicode9.0.0/ch05.pdf#G40630 // Roughly: consume at least one byte, // then validate one byte at a time and stop before the first unexpected byte // (which might be the valid start of the next byte sequence). let mut code_point; macro_rules! first_byte { ($mask: expr) => { code_point = u32::from(first_byte & $mask) } } macro_rules! continuation_byte { () => { continuation_byte!(0x80...0xBF) }; ($range: pat) => { match self.0.peek() { Some(&byte @ $range) => { code_point = (code_point << 6) | u32::from(byte & 0b0011_1111); self.0.next(); } _ => return Err(InvalidSequence(())) } } } match first_byte { 0x00...0x7F => { first_byte!(0b1111_1111); } 0xC2...0xDF => { first_byte!(0b0001_1111); continuation_byte!(); } 0xE0 => { first_byte!(0b0000_1111); continuation_byte!(0xA0...0xBF); // 0x80...0x9F here are overlong continuation_byte!(); } 0xE1...0xEC | 0xEE...0xEF => { first_byte!(0b0000_1111); continuation_byte!(); continuation_byte!(); } 0xED => { first_byte!(0b0000_1111); continuation_byte!(0x80...0x9F); // 0xA0..0xBF here are surrogates continuation_byte!(); } 0xF0 => { first_byte!(0b0000_0111); continuation_byte!(0x90...0xBF); // 0x80..0x8F here are overlong continuation_byte!(); continuation_byte!(); } 0xF1...0xF3 => { first_byte!(0b0000_0111); continuation_byte!(); continuation_byte!(); continuation_byte!(); } 0xF4 => { first_byte!(0b0000_0111); continuation_byte!(0x80...0x8F); // 0x90..0xBF here are beyond char::MAX continuation_byte!(); continuation_byte!(); } _ => return Err(InvalidSequence(())) // Illegal first byte, overlong, or beyond MAX } unsafe { Ok(from_u32_unchecked(code_point)) } }) } } #[unstable(feature = "decode_utf8", issue = "33906")] impl> FusedIterator for DecodeUtf8 {}