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Merge pull request #489 from yjh0502/master
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specialize hexadecimal sequence decoding
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@dtolnay
dtolnay authored Sep 26, 2018
2 parents bafc67b + d42a2e1 commit 1ef3da9
Showing 1 changed file with 70 additions and 20 deletions.
90 changes: 70 additions & 20 deletions src/read.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -83,6 +83,11 @@ pub trait Read<'de>: private::Sealed {
#[doc(hidden)]
fn ignore_str(&mut self) -> Result<()>;

/// Assumes the previous byte was a hex escape sequnce ('\u') in a string.
/// Parses next hexadecimal sequence.
#[doc(hidden)]
fn decode_hex_escape(&mut self) -> Result<u16>;

/// Switch raw buffering mode on.
///
/// This is used when deserializing `RawValue`.
Expand Down Expand Up @@ -339,6 +344,19 @@ where
}
}

fn decode_hex_escape<'s>(&'s mut self) -> Result<u16> {
let mut n = 0;
for _ in 0..4 {
match decode_hex_val(try!(next_or_eof(self))) {
None => return error(self, ErrorCode::InvalidEscape),
Some(val) => {
n = (n << 4) + val;
}
}
}
Ok(n)
}

#[cfg(feature = "raw_value")]
fn begin_raw_buffering(&mut self) {
self.raw_buffer = Some(Vec::new());
Expand Down Expand Up @@ -528,6 +546,23 @@ impl<'a> Read<'a> for SliceRead<'a> {
}
}

fn decode_hex_escape(&mut self) -> Result<u16> {
if self.index + 4 > self.slice.len() {
return error(self, ErrorCode::EofWhileParsingString);
}
let mut n = 0;
for _ in 0..4 {
match decode_hex_val(self.slice[self.index]) {
None => return error(self, ErrorCode::InvalidEscape),
Some(val) => {
n = (n << 4) + val;
}
}
self.index += 1;
}
Ok(n)
}

#[cfg(feature = "raw_value")]
fn begin_raw_buffering(&mut self) {
self.raw_buffering_start_index = self.index;
Expand Down Expand Up @@ -614,6 +649,10 @@ impl<'a> Read<'a> for StrRead<'a> {
self.delegate.ignore_str()
}

fn decode_hex_escape(&mut self) -> Result<u16> {
self.delegate.decode_hex_escape()
}

#[cfg(feature = "raw_value")]
fn begin_raw_buffering(&mut self) {
self.delegate.begin_raw_buffering()
Expand Down Expand Up @@ -690,7 +729,7 @@ fn parse_escape<'de, R: Read<'de>>(read: &mut R, scratch: &mut Vec<u8>) -> Resul
b'r' => scratch.push(b'\r'),
b't' => scratch.push(b'\t'),
b'u' => {
let c = match try!(decode_hex_escape(read)) {
let c = match try!(read.decode_hex_escape()) {
0xDC00...0xDFFF => {
return error(read, ErrorCode::LoneLeadingSurrogateInHexEscape);
}
Expand All @@ -705,7 +744,7 @@ fn parse_escape<'de, R: Read<'de>>(read: &mut R, scratch: &mut Vec<u8>) -> Resul
return error(read, ErrorCode::UnexpectedEndOfHexEscape);
}

let n2 = try!(decode_hex_escape(read));
let n2 = try!(read.decode_hex_escape());

if n2 < 0xDC00 || n2 > 0xDFFF {
return error(read, ErrorCode::LoneLeadingSurrogateInHexEscape);
Expand Down Expand Up @@ -747,7 +786,7 @@ fn ignore_escape<'de, R: ?Sized + Read<'de>>(read: &mut R) -> Result<()> {
match ch {
b'"' | b'\\' | b'/' | b'b' | b'f' | b'n' | b'r' | b't' => {}
b'u' => {
let n = match try!(decode_hex_escape(read)) {
let n = match try!(read.decode_hex_escape()) {
0xDC00...0xDFFF => {
return error(read, ErrorCode::LoneLeadingSurrogateInHexEscape);
}
Expand All @@ -762,7 +801,7 @@ fn ignore_escape<'de, R: ?Sized + Read<'de>>(read: &mut R) -> Result<()> {
return error(read, ErrorCode::UnexpectedEndOfHexEscape);
}

let n2 = try!(decode_hex_escape(read));
let n2 = try!(read.decode_hex_escape());

if n2 < 0xDC00 || n2 > 0xDFFF {
return error(read, ErrorCode::LoneLeadingSurrogateInHexEscape);
Expand All @@ -786,21 +825,32 @@ fn ignore_escape<'de, R: ?Sized + Read<'de>>(read: &mut R) -> Result<()> {
Ok(())
}

fn decode_hex_escape<'de, R: ?Sized + Read<'de>>(read: &mut R) -> Result<u16> {
let mut n = 0;
for _ in 0..4 {
n = match try!(next_or_eof(read)) {
c @ b'0'...b'9' => n * 16_u16 + ((c as u16) - (b'0' as u16)),
b'a' | b'A' => n * 16_u16 + 10_u16,
b'b' | b'B' => n * 16_u16 + 11_u16,
b'c' | b'C' => n * 16_u16 + 12_u16,
b'd' | b'D' => n * 16_u16 + 13_u16,
b'e' | b'E' => n * 16_u16 + 14_u16,
b'f' | b'F' => n * 16_u16 + 15_u16,
_ => {
return error(read, ErrorCode::InvalidEscape);
}
};
#[cfg_attr(rustfmt, rustfmt_skip)]
static HEX: [u8; 256] = [
// 1 2 3 4 5 6 7 8 9 A B C D E F
255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255, // 0
255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255, // 1
255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255, // 2
0, 1, 2, 3, 4, 5, 6, 7, 8, 9,255,255,255,255,255,255, // 3
255, 10, 11, 12, 13, 14, 15,255,255,255,255,255,255,255,255,255, // 4
255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255, // 5
255, 10, 11, 12, 13, 14, 15,255,255,255,255,255,255,255,255,255, // 6
255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255, // 7
255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255, // 8
255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255, // 9
255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255, // A
255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255, // B
255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255, // C
255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255, // D
255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255, // E
255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255, // F
];

fn decode_hex_val(val: u8) -> Option<u16> {
let n = HEX[val as usize] as u16;
if n == 255 {
None
} else {
Some(n)
}
Ok(n)
}

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