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348: Specialize Intersperse::fold r=bluss a=jswrenn Overriding `Intersperse::fold`'s default implementation makes iteration with `for_each` approximately 10× faster than external iteration, and approximately 20× faster than `for_each` with an un-specialized `fold`: ``` $ cargo bench -- specialization specialization::intersperse::internal_specialized 64 ns/iter (+/- 1) specialization::intersperse::external 638 ns/iter (+/- 45) specialization::intersperse::internal_unspecialized 1,274 ns/iter (+/- 131) ``` Co-authored-by: Jack Wrenn <me@jswrenn.com>
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Original file line number | Diff line number | Diff line change |
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#![feature(test)] | ||
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extern crate test; | ||
extern crate itertools; | ||
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use itertools::Itertools; | ||
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struct Unspecialized<I>(I); | ||
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impl<I> Iterator for Unspecialized<I> | ||
where I: Iterator | ||
{ | ||
type Item = I::Item; | ||
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#[inline(always)] | ||
fn next(&mut self) -> Option<I::Item> { | ||
self.0.next() | ||
} | ||
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#[inline(always)] | ||
fn size_hint(&self) -> (usize, Option<usize>) { | ||
self.0.size_hint() | ||
} | ||
} | ||
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mod specialization { | ||
use super::*; | ||
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mod intersperse { | ||
use super::*; | ||
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#[bench] | ||
fn external(b: &mut test::Bencher) | ||
{ | ||
let arr = [1; 1024]; | ||
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b.iter(|| { | ||
let mut sum = 0; | ||
for &x in arr.into_iter().intersperse(&0) { | ||
sum += x; | ||
} | ||
sum | ||
}) | ||
} | ||
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#[bench] | ||
fn internal_specialized(b: &mut test::Bencher) | ||
{ | ||
let arr = [1; 1024]; | ||
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b.iter(|| { | ||
arr.into_iter().intersperse(&0).fold(0, |acc, x| acc + x) | ||
}) | ||
} | ||
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#[bench] | ||
fn internal_unspecialized(b: &mut test::Bencher) | ||
{ | ||
let arr = [1; 1024]; | ||
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b.iter(|| { | ||
Unspecialized(arr.into_iter().intersperse(&0)).fold(0, |acc, x| acc + x) | ||
}) | ||
} | ||
} | ||
} |
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extern crate itertools; | ||
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use itertools::Itertools; | ||
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#[test] | ||
fn specialization_intersperse() { | ||
let mut iter = (1..2).intersperse(0); | ||
iter.clone().for_each(|x| assert_eq!(Some(x), iter.next())); | ||
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let mut iter = (1..3).intersperse(0); | ||
iter.clone().for_each(|x| assert_eq!(Some(x), iter.next())); | ||
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let mut iter = (1..4).intersperse(0); | ||
iter.clone().for_each(|x| assert_eq!(Some(x), iter.next())); | ||
} |