HaoYang670 commented on issue #1400:
URL: https://github.com/apache/arrow-rs/issues/1400#issuecomment-1059753488
> Interesting, I'm actually seeing the opposite effect, with `fold` being
faster. This is running on an Amd 3700U laptop. The generated code for `fold`
and `reduce` seems to differ in that `reduce` contains several branches while
`fold` looks relatively branchless. Different CPUs might handle one or the
other better, although I would expect the branchless to win in the benchmark
since the input consists of random numbers. I don't have any good explanation
why this effects the null handling loop.
>
> `
More interesting! My desktop uses Intel i7 10700K processors.
Also, I am curious about why the compiler generates different code for
`fold` and `reduce`. The `reduce` just uses `fold` in its implementation:
```rust
#[inline]
#[stable(feature = "iterator_fold_self", since = "1.51.0")]
fn reduce<F>(mut self, f: F) -> Option<Self::Item>
where
Self: Sized,
F: FnMut(Self::Item, Self::Item) -> Self::Item,
{
let first = self.next()?;
Some(self.fold(first, f))
}
```
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