Optimize slice {Chunks,Windows}::nth #138562
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Luracasmus
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Mar 16, 2025
Generates branchless code
This avoids generating extra instructions that needlessly modify the slice's pointer
Noratrieb
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Noratrieb
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Mar 24, 2025
| @@ -1429,7 +1429,7 @@ impl<'a, T> DoubleEndedIterator for Windows<'a, T> { | |||
| fn nth_back(&mut self, n: usize) -> Option<Self::Item> { | |||
| let (end, overflow) = self.v.len().overflowing_sub(n); | |||
| if end < self.size.get() || overflow { | |||
| self.v = &[]; | |||
| self.v = &self.v[..0]; | |||
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I think it would make sense to also add the // cheaper than &[] comment to all these cases as well, it's not immediately obvious that it is
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I've noticed that the
nthfunctions on slice iters had non-optimized-out bounds checks.The new implementation even generates branchless code.