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Improve speed of fmt::Debug for str and char #28662

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merged 4 commits into from
Oct 3, 2015
Merged

Improve speed of fmt::Debug for str and char #28662

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24b5d3a
Improve speed of `fmt::Debug` for `str` and `char`
semmaz Sep 23, 2015
025ca11
Add `fmt::Debug` string escape tests
semmaz Sep 29, 2015
d2d0872
Implement `size_hint` for `EscapeDefault`
semmaz Sep 29, 2015
0294098
Implement `size_hint` for `EscapeUnicode`
semmaz Sep 30, 2015
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31 changes: 27 additions & 4 deletions src/libcore/char.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -185,9 +185,7 @@ impl CharExt for char {
'\t' => EscapeDefaultState::Backslash('t'),
'\r' => EscapeDefaultState::Backslash('r'),
'\n' => EscapeDefaultState::Backslash('n'),
'\\' => EscapeDefaultState::Backslash('\\'),
'\'' => EscapeDefaultState::Backslash('\''),
'"' => EscapeDefaultState::Backslash('"'),
'\\' | '\'' | '"' => EscapeDefaultState::Backslash(self),
'\x20' ... '\x7e' => EscapeDefaultState::Char(self),
_ => EscapeDefaultState::Unicode(self.escape_unicode())
};
Expand Down Expand Up @@ -344,6 +342,22 @@ impl Iterator for EscapeUnicode {
EscapeUnicodeState::Done => None,
}
}

fn size_hint(&self) -> (usize, Option<usize>) {
let mut n = 0;
while (self.c as usize) >> (4 * (n + 1)) != 0 {
n += 1;
}
let n = match self.state {
EscapeUnicodeState::Backslash => n + 5,
EscapeUnicodeState::Type => n + 4,
EscapeUnicodeState::LeftBrace => n + 3,
EscapeUnicodeState::Value(offset) => offset + 2,
EscapeUnicodeState::RightBrace => 1,
EscapeUnicodeState::Done => 0,
};
(n, Some(n))
}
}

/// An iterator over the characters that represent a `char`, escaped
Expand Down Expand Up @@ -377,7 +391,16 @@ impl Iterator for EscapeDefault {
Some(c)
}
EscapeDefaultState::Done => None,
EscapeDefaultState::Unicode(ref mut iter) => iter.next()
EscapeDefaultState::Unicode(ref mut iter) => iter.next(),
}
}

fn size_hint(&self) -> (usize, Option<usize>) {
match self.state {
EscapeDefaultState::Char(_) => (1, Some(1)),
EscapeDefaultState::Backslash(_) => (2, Some(2)),
EscapeDefaultState::Unicode(ref iter) => iter.size_hint(),
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For now if you want to retain the same speed as the original implementation you had this can possibly just be (0, None) (e.g. the default return value) and that way you don't have to bother with the calculations about the width of a character perhaps?

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I actually tested this with (0, Some(10)) as return value here, before adding size_hint to EscapeUnicode and using it here. Didn't noticed any significant difference, so I guess slowdown comes from iterator construction. I'll double check that though.

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And it is iterator construction.

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Ah ok, thanks for checking!

EscapeDefaultState::Done => (0, Some(0)),
}
}
}
23 changes: 16 additions & 7 deletions src/libcore/fmt/mod.rs
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Expand Up @@ -1310,11 +1310,21 @@ impl Display for bool {
#[stable(feature = "rust1", since = "1.0.0")]
impl Debug for str {
fn fmt(&self, f: &mut Formatter) -> Result {
try!(write!(f, "\""));
for c in self.chars().flat_map(|c| c.escape_default()) {
try!(f.write_char(c))
try!(f.write_char('"'));
let mut from = 0;
for (i, c) in self.char_indices() {
let esc = c.escape_default();
// If char needs escaping, flush backlog so far and write, else skip
if esc.size_hint() != (1, Some(1)) {
try!(f.write_str(&self[from..i]));
for c in esc {
try!(f.write_char(c));
}
from = i + c.len_utf8();
}
}
write!(f, "\"")
try!(f.write_str(&self[from..]));
f.write_char('"')
}
}

Expand All @@ -1328,12 +1338,11 @@ impl Display for str {
#[stable(feature = "rust1", since = "1.0.0")]
impl Debug for char {
fn fmt(&self, f: &mut Formatter) -> Result {
use char::CharExt;
try!(write!(f, "'"));
try!(f.write_char('\''));
for c in self.escape_default() {
try!(f.write_char(c))
}
write!(f, "'")
f.write_char('\'')
}
}

Expand Down
4 changes: 4 additions & 0 deletions src/test/run-pass/ifmt.rs
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Expand Up @@ -74,6 +74,10 @@ pub fn main() {
t!(format!("{:?}", 10_usize), "10");
t!(format!("{:?}", "true"), "\"true\"");
t!(format!("{:?}", "foo\nbar"), "\"foo\\nbar\"");
t!(format!("{:?}", "foo\n\"bar\"\r\n\'baz\'\t\\qux\\"),
r#""foo\n\"bar\"\r\n\'baz\'\t\\qux\\""#);
t!(format!("{:?}", "foo\0bar\x01baz\u{3b1}q\u{75}x"),
r#""foo\u{0}bar\u{1}baz\u{3b1}qux""#);
t!(format!("{:o}", 10_usize), "12");
t!(format!("{:x}", 10_usize), "a");
t!(format!("{:X}", 10_usize), "A");
Expand Down