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Remove some redundant parts from unrolled_find_u16s #74289

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Merged
merged 3 commits into from
Aug 8, 2020
Merged

Remove some redundant parts from unrolled_find_u16s #74289

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a5d0c2c
Remove redundant len binding
tesuji Jul 13, 2020
34c343a
Make use of macro to avoid repetition
tesuji Jul 13, 2020
f55e4d0
Get pointer from address of c directly
tesuji Jul 13, 2020
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41 changes: 13 additions & 28 deletions library/std/src/sys/windows/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -99,43 +99,28 @@ pub fn decode_error_kind(errno: i32) -> ErrorKind {

pub fn unrolled_find_u16s(needle: u16, haystack: &[u16]) -> Option<usize> {
let ptr = haystack.as_ptr();
let mut len = haystack.len();
let mut start = &haystack[..];

// For performance reasons unfold the loop eight times.
while len >= 8 {
if start[0] == needle {
return Some((start.as_ptr() as usize - ptr as usize) / 2);
}
if start[1] == needle {
return Some((start[1..].as_ptr() as usize - ptr as usize) / 2);
}
if start[2] == needle {
return Some((start[2..].as_ptr() as usize - ptr as usize) / 2);
}
if start[3] == needle {
return Some((start[3..].as_ptr() as usize - ptr as usize) / 2);
}
if start[4] == needle {
return Some((start[4..].as_ptr() as usize - ptr as usize) / 2);
}
if start[5] == needle {
return Some((start[5..].as_ptr() as usize - ptr as usize) / 2);
}
if start[6] == needle {
return Some((start[6..].as_ptr() as usize - ptr as usize) / 2);
}
if start[7] == needle {
return Some((start[7..].as_ptr() as usize - ptr as usize) / 2);
while start.len() >= 8 {
macro_rules! if_return {
($($n:literal,)+) => {
$(
if start[$n] == needle {
return Some((&start[$n] as *const u16 as usize - ptr as usize) / 2);
}
)+
}
}

if_return!(0, 1, 2, 3, 4, 5, 6, 7,);

start = &start[8..];
len -= 8;
}

for (i, c) in start.iter().enumerate() {
for c in start {
if *c == needle {
return Some((start.as_ptr() as usize - ptr as usize) / 2 + i);
return Some((c as *const u16 as usize - ptr as usize) / 2);
}
}
None
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