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See https://github.com/rust-lang/rfcs/pull/2791 for motivation.
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Remove manual unrolling from slice::Iter(Mut)::try_fold
While this definitely helps sometimes (particularly for trivial closures), it's also a pessimization sometimes, so it's better to leave this to (hypothetical) future LLVM improvements instead of forcing this on everyone.
I think it's better for the advice to be that sometimes you need to unroll manually than you sometimes need to not-unroll manually (like #64545).
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For context see https://github.com/rust-lang/rust/pull/64572#issuecomment-532961046
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While this definitely helps sometimes (particularly for trivial closures), it's also a pessimization sometimes, so it's better to leave this to (hypothetical) future LLVM improvements instead of forcing this on everyone.
I think it's better for the advice to be that sometimes you need to unroll manually than you sometimes need to not-unroll manually (like #64545).
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r=scottmcm
Implement `nth_back` for ChunksExactMut
This is a part of #54054.
r? @scottmcm
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Improve `ptr_rotate` performance, tests, and benches
The corresponding issue is #61784. I am not actually sure if miri can handle the test, but I can change the commit if necessary.
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relative links do not work because this is included in several places
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Co-Authored-By: Mazdak Farrokhzad <twingoow@gmail.com>
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squash of all commits for nth_back on ChunksMut
wip nth_back for chunks_mut
working chunksmut
fixed nth_back for chunksmut
Signed-off-by: wizAmit <amitforfriends_dns@yahoo.com>
r? @timvermeulen
r? @scottmcm
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Rename .cap() methods to .capacity()
As mentioned in #60316, there are a few `.cap()` methods, which seem out-of-place because such methods are called `.capacity()` in the rest of the code.
This PR renames them to `.capacity()` but leaves `RawVec::cap()` in there for backwards compatibility.
I didn't try to mark the old version as "deprecated", because I guess this would cause too much noise.
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explain how to search in slice without owned data
Cc https://github.com/rust-lang/rust/issues/62367
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Fix repeated wording in slice documentation
Changes `of the slice of the slice` to `of the slice` in the chunk- and friends documentation of slices
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core: check for pointer equality when comparing Eq slices
Because `Eq` types must be reflexively equal, an equal-length slice to the same memory location must be equal.
This is related to #33892 (and #32699) answering this comment from that PR:
> Great! One more easy question: why does this optimization not apply in the non-BytewiseEquality implementation directly above?
Because slices of non-reflexively equal types (like `f64`) are not equal even if it's the same slice. But if the types are `Eq`, we can use this same-address optimization, which this PR implements. Obviously this changes behavior if types violate the reflexivity condition of `Eq`, because their impls of `PartialEq` will no longer be called per-item, but 🤷♂ .
It's not clear how often this optimization comes up in the real world outside of the same-`&str` case covered by #33892, so **I'm requesting a perf run** (on MacOS today, so can't run `rustc_perf` myself). I'm going ahead and making the PR on the basis of being surprised things didn't already work this way.
This is my first time hacking rust itself, so as a perf sanity check I ran `./x.py bench --stage 0 src/lib{std,alloc}`, but the differences were noisy.
To make the existing specialization for `BytewiseEquality` explicit, it's now a supertrait of `Eq + Copy`. `Eq` should be sufficient, but `Copy` was included for clarity.
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Only call the closure parameter of Iterator::is_sorted_by_key once per item
See https://github.com/rust-lang/rust/issues/53485#issuecomment-472314004.
This changes `Iterator::is_sorted_by_key` to only call the given closure once for each item, which allows us to pass the items to the closure by value instead of by reference.
**Important**: `is_sorted_by_key` for slices and slice iterators is now no longer implemented in terms of the custom `slice::Iter::is_sorted_by` implementation. It's a trade-off: we could forward `slice::Iter::is_sorted_by_key` to it directly for potential SIMD benefits, but that would mean that the closure is potentially called twice for (almost) every element of the slice.
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wip nth_back for chunks_mut
working chunksmut
fixed nth_back for chunksmut
Signed-off-by: wizAmit <amitforfriends_dns@yahoo.com>
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wip nth_back for chunks_exact
working nth_back for chunks exact
Signed-off-by: wizAmit <amitforfriends_dns@yahoo.com>
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Implement nth_back for slice::{Iter, IterMut}
Part of #54054.
I implemented `nth_back` as straightforwardly as I could, and then slightly changed `nth` to match `nth_back`. I believe I did so correctly, but please double-check 🙂
I also added the helper methods `zst_shrink`, `next_unchecked`, and `next_back_unchecked` to get rid of some duplicated code. These changes hopefully make this code easier to understand for new contributors like me.
I noticed the `is_empty!` and `len!` macros which sole purpose seems to be inlining, according to the comment right above them, but the `is_empty` and `len` methods are already marked with `#[inline(always)]`. Does that mean we could replace these macros with method calls, without affecting anything? I'd love to get rid of them.
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Stabilize copy_within
Closes #54236.
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Because Eq types must be reflexively equal, an equal-length slice to the
same memory location must be equal.
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This ensures we won't accidentally read *src or *dest even when count = 0.
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Feature/nth back chunks
A succinct implementation for nth_back on chunks. Thank you @timvermeulen for the guidance.
r? @timvermeulen
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Implement nth_back for RChunks(Exact)(Mut)
Part of #54054.
These implementations may not be optimal because of the use of `self.len()`, but it's quite cheap and simplifies the code a lot.
There's quite some duplication going on here, I wouldn't mind cleaning this up later. A good next step would probably be to add private `split_off_up_to`/`split_off_from` helper methods for slices since their behavior is commonly useful throughout the `Chunks` types.
r? @scottmcm
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DoubleEndedIterators."
This reverts commit 3e86cf36b5114f201868bf459934fe346a76a2d4.
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