Faster midpoint calculation for binary_search_by
#128236
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This takes advantage of the fact that slices can only have a maximum of `isize::MAX` elements, which means that the midpoint can be calculated using `(left + right) / 2` instead of `left + (right - left) / 2`. The old calculation is kept only for ZST slices which can have up to `usize::MAX` elements. Comparison with previous version: https://rust.godbolt.org/z/YccscWoqv
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r? @Nilstrieb rustbot has assigned @Nilstrieb. Use |
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CC similar attempt #127007 |
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Actually, I've been doing more tests and I get much better results by just reverting to the original implementation from #45333 + forcing LLVM to emit CMOVs. |
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This takes advantage of the fact that slices can only have a maximum of
isize::MAXelements, which means that the midpoint can be calculated using(left + right) / 2instead ofleft + (right - left) / 2.The old calculation is kept only for ZST slices which can have up to
usize::MAXelements.Comparison with previous version: https://rust.godbolt.org/z/YccscWoqv