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Specialize RepeatN::[r]fold #821

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merged 2 commits into from Dec 15, 2023
Merged

Specialize RepeatN::[r]fold #821

merged 2 commits into from Dec 15, 2023

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Philippe-Cholet
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@Philippe-Cholet Philippe-Cholet commented Dec 14, 2023 •
edited

Related to #755

cargo bench --bench specializations "repeat_n/r?fold"

repeat_n/fold           time:   [550.53 ns 553.84 ns 557.21 ns]
repeat_n/fold           time:   [267.32 ns 268.75 ns 270.78 ns]
                        change: [-52.797% -51.769% -50.705%]

repeat_n/rfold          time:   [546.41 ns 547.81 ns 549.27 ns]
repeat_n/rfold          time:   [268.31 ns 269.45 ns 271.03 ns]
                        change: [-51.214% -50.990% -50.727%]

@Philippe-Cholet Philippe-Cholet added this to the next milestone Dec 14, 2023
phimuemue
phimuemue approved these changes Dec 15, 2023
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Thanks.

src/repeatn.rs
Self { elt: Some(elt), n } => {
debug_assert!(n > 0);
init = (1..n).map(|_| elt.clone()).fold(init, &mut f);
f(init, elt)
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Avoiding the clone. Nice.

src/repeatn.rs
F: FnMut(B, Self::Item) -> B,
{
match self {
Self { elt: Some(elt), n } => {
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Here, we take elt as reference if there's still work to do, whereas fn next uses self.n > 1. Should we canonicalize?

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I'm not sure there is a real benefit to win here. Feel free to investigate.

@phimuemue phimuemue added this pull request to the merge queue Dec 15, 2023
Merged via the queue into rust-itertools:master with commit db0311c Dec 15, 2023
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@Philippe-Cholet Philippe-Cholet deleted the fold-repeat-n branch December 15, 2023 15:24
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