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Speed up string printing

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This commit is contained in:
David Tolnay 2016-06-28 00:02:07 -07:00
parent 0d1e16bdaf
commit fc436ebd73
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1 changed files with 47 additions and 16 deletions
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63
json/src/ser.rs
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@ -488,7 +488,8 @@ impl<'a> Formatter for PrettyFormatter<'a> {
}
}
/// Serializes and escapes a `&[u8]` into a JSON string.
/// DEPRECATED. Will be removed in 0.8.0.
/// https://github.com/serde-rs/json/issues/60
#[inline]
pub fn escape_bytes<W>(wr: &mut W, bytes: &[u8]) -> Result<()>
where W: io::Write
@ -497,26 +498,25 @@ pub fn escape_bytes<W>(wr: &mut W, bytes: &[u8]) -> Result<()>
let mut start = 0;
for (i, byte) in bytes.iter().enumerate() {
let escaped = match *byte {
b'"' => b"\\\"",
b'\\' => b"\\\\",
b'\x08' => b"\\b",
b'\x0c' => b"\\f",
b'\n' => b"\\n",
b'\r' => b"\\r",
b'\t' => b"\\t",
b'\x00' ... b'\x1F' => b"\\u",
_ => { continue; }
};
for (i, &byte) in bytes.iter().enumerate() {
let escape = ESCAPE[byte as usize];
if escape == 0 {
continue;
}
if start < i {
try!(wr.write_all(&bytes[start..i]));
}
try!(wr.write_all(escaped));
if escaped[1] == b'u' {
try!(write!(wr, "{:04x}", *byte));
if escape == b'u' {
static HEX_DIGITS: [u8; 16] = *b"0123456789abcdef";
try!(wr.write_all(&[
b'\\', b'u', b'0', b'0',
HEX_DIGITS[(byte >> 4) as usize],
HEX_DIGITS[(byte & 0xF) as usize],
]));
} else {
try!(wr.write_all(&[b'\\', escape]));
}
start = i + 1;
@ -530,6 +530,37 @@ pub fn escape_bytes<W>(wr: &mut W, bytes: &[u8]) -> Result<()>
Ok(())
}
const BB: u8 = b'b'; // \x08
const TT: u8 = b't'; // \x09
const NN: u8 = b'n'; // \x0A
const FF: u8 = b'f'; // \x0C
const RR: u8 = b'r'; // \x0D
const QU: u8 = b'"'; // \x22
const BS: u8 = b'\\'; // \x5C
const U: u8 = b'u'; // \x00...\x1F except the ones above
// Lookup table of escape sequences. A value of b'x' at index i means that byte
// i is escaped as "\x" in JSON. A value of 0 means that byte i is not escaped.
static ESCAPE: [u8; 256] = [
// 1 2 3 4 5 6 7 8 9 A B C D E F
U, U, U, U, U, U, U, U, BB, TT, NN, U, FF, RR, U, U, // 0
U, U, U, U, U, U, U, U, U, U, U, U, U, U, U, U, // 1
0, 0, QU, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // 2
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // 3
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // 4
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, BS, 0, 0, 0, // 5
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // 6
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // 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, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // C
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // D
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // E
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // F
];
/// Serializes and escapes a `&str` into a JSON string.
#[inline]
pub fn escape_str<W>(wr: &mut W, value: &str) -> Result<()>