The addition of `core::iter::zip` (#82917) set a precedent for adding
plain functions for iterator adaptors. Adding `chain` makes it a little
easier to `chain` two iterators.
```
for (x, y) in chain(xs, ys) {}
// vs.
for (x, y) in xs.into_iter().chain(ys) {}
```
Change f32::midpoint to upcast to f64
This has been verified by kani as a correct optimization
see: https://github.com/rust-lang/rust/issues/110840#issuecomment-1942587398
The new implementation is branchless and only differs in which NaN values are produced (if any are produced at all), which is fine to change. Aside from NaN handling, this implementation produces bitwise identical results to the original implementation.
Question: do we need a codegen test for this? I didn't add one, since the original PR #92048 didn't have any codegen tests.
This has been verified by kani as a correct optimization
see: https://github.com/rust-lang/rust/issues/110840#issuecomment-1942587398
The new implementation is branchless, and only differs in which NaN
values are produced (if any are produced at all). Which is fine to change.
Aside from NaN handling, this implementation produces bitwise identical
results to the original implementation.
The new implementation is gated on targets that have a fast 64-bit
floating point implementation in hardware, and on WASM.
Expand `for_loops_over_fallibles` lint to lint on fallibles behind references.
Extends the scope of the (warn-by-default) lint `for_loops_over_fallibles` from just `for _ in x` where `x: Option<_>/Result<_, _>` to also cover `x: &(mut) Option<_>/Result<_>`
```rs
fn main() {
// Current lints
for _ in Some(42) {}
for _ in Ok::<_, i32>(42) {}
// New lints
for _ in &Some(42) {}
for _ in &mut Some(42) {}
for _ in &Ok::<_, i32>(42) {}
for _ in &mut Ok::<_, i32>(42) {}
// Should not lint
for _ in Some(42).into_iter() {}
for _ in Some(42).iter() {}
for _ in Some(42).iter_mut() {}
for _ in Ok::<_, i32>(42).into_iter() {}
for _ in Ok::<_, i32>(42).iter() {}
for _ in Ok::<_, i32>(42).iter_mut() {}
}
```
<details><summary><code>cargo build</code> diff</summary>
```diff
diff --git a/old.out b/new.out
index 84215aa..ca195a7 100644
--- a/old.out
+++ b/new.out
`@@` -1,33 +1,93 `@@`
warning: for loop over an `Option`. This is more readably written as an `if let` statement
--> src/main.rs:3:14
|
3 | for _ in Some(42) {}
| ^^^^^^^^
|
= note: `#[warn(for_loops_over_fallibles)]` on by default
help: to check pattern in a loop use `while let`
|
3 | while let Some(_) = Some(42) {}
| ~~~~~~~~~~~~~~~ ~~~
help: consider using `if let` to clear intent
|
3 | if let Some(_) = Some(42) {}
| ~~~~~~~~~~~~ ~~~
warning: for loop over a `Result`. This is more readably written as an `if let` statement
--> src/main.rs:4:14
|
4 | for _ in Ok::<_, i32>(42) {}
| ^^^^^^^^^^^^^^^^
|
help: to check pattern in a loop use `while let`
|
4 | while let Ok(_) = Ok::<_, i32>(42) {}
| ~~~~~~~~~~~~~ ~~~
help: consider using `if let` to clear intent
|
4 | if let Ok(_) = Ok::<_, i32>(42) {}
| ~~~~~~~~~~ ~~~
-warning: `for-loops-over-fallibles` (bin "for-loops-over-fallibles") generated 2 warnings
- Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.04s
+warning: for loop over a `&Option`. This is more readably written as an `if let` statement
+ --> src/main.rs:7:14
+ |
+7 | for _ in &Some(42) {}
+ | ^^^^^^^^^
+ |
+help: to check pattern in a loop use `while let`
+ |
+7 | while let Some(_) = &Some(42) {}
+ | ~~~~~~~~~~~~~~~ ~~~
+help: consider using `if let` to clear intent
+ |
+7 | if let Some(_) = &Some(42) {}
+ | ~~~~~~~~~~~~ ~~~
+
+warning: for loop over a `&mut Option`. This is more readably written as an `if let` statement
+ --> src/main.rs:8:14
+ |
+8 | for _ in &mut Some(42) {}
+ | ^^^^^^^^^^^^^
+ |
+help: to check pattern in a loop use `while let`
+ |
+8 | while let Some(_) = &mut Some(42) {}
+ | ~~~~~~~~~~~~~~~ ~~~
+help: consider using `if let` to clear intent
+ |
+8 | if let Some(_) = &mut Some(42) {}
+ | ~~~~~~~~~~~~ ~~~
+
+warning: for loop over a `&Result`. This is more readably written as an `if let` statement
+ --> src/main.rs:9:14
+ |
+9 | for _ in &Ok::<_, i32>(42) {}
+ | ^^^^^^^^^^^^^^^^^
+ |
+help: to check pattern in a loop use `while let`
+ |
+9 | while let Ok(_) = &Ok::<_, i32>(42) {}
+ | ~~~~~~~~~~~~~ ~~~
+help: consider using `if let` to clear intent
+ |
+9 | if let Ok(_) = &Ok::<_, i32>(42) {}
+ | ~~~~~~~~~~ ~~~
+
+warning: for loop over a `&mut Result`. This is more readably written as an `if let` statement
+ --> src/main.rs:10:14
+ |
+10 | for _ in &mut Ok::<_, i32>(42) {}
+ | ^^^^^^^^^^^^^^^^^^^^^
+ |
+help: to check pattern in a loop use `while let`
+ |
+10 | while let Ok(_) = &mut Ok::<_, i32>(42) {}
+ | ~~~~~~~~~~~~~ ~~~
+help: consider using `if let` to clear intent
+ |
+10 | if let Ok(_) = &mut Ok::<_, i32>(42) {}
+ | ~~~~~~~~~~ ~~~
+
+warning: `for-loops-over-fallibles` (bin "for-loops-over-fallibles") generated 6 warnings
+ Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.02s
```
</details>
-----
Question:
* ~~Currently, the article `an` is used for `&Option`, and `&mut Option` in the lint diagnostic, since that's what `Option` uses. Is this okay or should it be changed? (likewise, `a` is used for `&Result` and `&mut Result`)~~ The article `a` is used for `&Option`, `&mut Option`, `&Result`, `&mut Result` and (as before) `Result`. Only `Option` uses `an` (as before).
`@rustbot` label +A-lint
- `slice::sort` -> driftsort
https://github.com/Voultapher/sort-research-rs/blob/main/writeup/driftsort_introduction/text.md
- `slice::sort_unstable` -> ipnsort
https://github.com/Voultapher/sort-research-rs/blob/main/writeup/ipnsort_introduction/text.md
Replaces the sort implementations with tailor made ones that strike a
balance of run-time, compile-time and binary-size, yielding run-time and
compile-time improvements. Regressing binary-size for `slice::sort`
while improving it for `slice::sort_unstable`. All while upholding the
existing soft and hard safety guarantees, and even extending the soft
guarantees, detecting strict weak ordering violations with a high chance
and reporting it to users via a panic.
In addition the implementation of `select_nth_unstable` is also adapted
as it uses `slice::sort_unstable` internals.
Add `Ord::cmp` for primitives as a `BinOp` in MIR
Update: most of this OP was written months ago. See https://github.com/rust-lang/rust/pull/118310#issuecomment-2016940014 below for where we got to recently that made it ready for review.
---
There are dozens of reasonable ways to implement `Ord::cmp` for integers using comparison, bit-ops, and branches. Those differences are irrelevant at the rust level, however, so we can make things better by adding `BinOp::Cmp` at the MIR level:
1. Exactly how to implement it is left up to the backends, so LLVM can use whatever pattern its optimizer best recognizes and cranelift can use whichever pattern codegens the fastest.
2. By not inlining those details for every use of `cmp`, we drastically reduce the amount of MIR generated for `derive`d `PartialOrd`, while also making it more amenable to MIR-level optimizations.
Having extremely careful `if` ordering to μoptimize resource usage on broadwell (#63767) is great, but it really feels to me like libcore is the wrong place to put that logic. Similarly, using subtraction [tricks](https://graphics.stanford.edu/~seander/bithacks.html#CopyIntegerSign) (#105840) is arguably even nicer, but depends on the optimizer understanding it (https://github.com/llvm/llvm-project/issues/73417) to be practical. Or maybe [bitor is better than add](https://discourse.llvm.org/t/representing-in-ir/67369/2?u=scottmcm)? But maybe only on a future version that [has `or disjoint` support](https://discourse.llvm.org/t/rfc-add-or-disjoint-flag/75036?u=scottmcm)? And just because one of those forms happens to be good for LLVM, there's no guarantee that it'd be the same form that GCC or Cranelift would rather see -- especially given their very different optimizers. Not to mention that if LLVM gets a spaceship intrinsic -- [which it should](https://rust-lang.zulipchat.com/#narrow/stream/131828-t-compiler/topic/Suboptimal.20inlining.20in.20std.20function.20.60binary_search.60/near/404250586) -- we'll need at least a rustc intrinsic to be able to call it.
As for simplifying it in Rust, we now regularly inline `{integer}::partial_cmp`, but it's quite a large amount of IR. The best way to see that is with 8811efa88b (diff-d134c32d028fbe2bf835fef2df9aca9d13332dd82284ff21ee7ebf717bfa4765R113) -- I added a new pre-codegen MIR test for a simple 3-tuple struct, and this PR change it from 36 locals and 26 basic blocks down to 24 locals and 8 basic blocks. Even better, as soon as the construct-`Some`-then-match-it-in-same-BB noise is cleaned up, this'll expose the `Cmp == 0` branches clearly in MIR, so that an InstCombine (#105808) can simplify that to just a `BinOp::Eq` and thus fix some of our generated code perf issues. (Tracking that through today's `if a < b { Less } else if a == b { Equal } else { Greater }` would be *much* harder.)
---
r? `@ghost`
But first I should check that perf is ok with this
~~...and my true nemesis, tidy.~~
Make `io::BorrowedCursor::advance` safe
This also keeps the old `advance` method under `advance_unchecked` name.
This makes pattern like `std::io::default_read_buf` safe to write.
Rename MaybeUninit::write_slice
A step to push #79995 forward.
https://github.com/rust-lang/libs-team/issues/122 also suggested to make them inherent methods, but they can't be — they'd conflict with slice's regular methods.
core: add Duration constructors
Add more `Duration` constructors.
Tracking issue: #120301.
These match similar convenience constructors available on both `chrono::Duration` and `time::Duration`.
What's the best ordering for these with respect to the existing constructors?
stabilise array methods
Closes#76118
Stabilises the remaining array methods
FCP is yet to be carried out for this
There wasn't a clear consensus on the naming, but all the other alternatives had some flaws as discussed in the tracking issue and there was a silence on this issue for a year
Implement iterator specialization traits on more adapters
This adds
* `TrustedLen` to `Skip` and `StepBy`
* `TrustedRandomAccess` to `Skip`
* `InPlaceIterable` and `SourceIter` to `Copied` and `Cloned`
The first two might improve performance in the compiler itself since `skip` is used in several places. Constellations that would exercise the last point are probably rare since it would require an owning iterator that has references as Items somewhere in its iterator pipeline.
Improvements for `Skip`:
```
# old
test iter::bench_skip_trusted_random_access ... bench: 8,335 ns/iter (+/- 90)
# new
test iter::bench_skip_trusted_random_access ... bench: 2,753 ns/iter (+/- 27)
```
Add Ipv6Addr::is_ipv4_mapped
This change consists of cherry-picking the content from the original PR[1], which got closed due to inactivity, and applying the following changes:
* Resolving merge conflicts (obviously)
* Linked to to_ipv4_mapped instead of to_ipv4 in the documentation (seems more appropriate)
* Added the must_use and rustc_const_unstable attributes the original didn't have
I think it's a reasonably useful method to have.
[1] https://github.com/rust-lang/rust/pull/86490
Use `bool` instead of `PartiolOrd` as return value of the comparison closure in `{slice,Iteraotr}::is_sorted_by`
Changes the function signature of the closure given to `{slice,Iteraotr}::is_sorted_by` to return a `bool` instead of a `PartiolOrd` as suggested by the libs-api team here: https://github.com/rust-lang/rust/issues/53485#issuecomment-1766411980.
This means these functions now return true if the closure returns true for all the pairs of values.
Stabilize single-field offset_of
This PR stabilizes offset_of for a single field. There has been some further discussion at https://github.com/rust-lang/rust/issues/106655 about whether this is advisable; I'm opening the PR anyway so that the code is available.
Change return type of unstable `Waker::noop()` from `Waker` to `&Waker`.
The advantage of this is that it does not need to be assigned to a variable to be used in a `Context` creation, which is the most common thing to want to do with a noop waker. It also avoids unnecessarily executing the dynamically dispatched drop function when the noop waker is dropped.
If an owned noop waker is desired, it can be created by cloning, but the reverse is harder to do since it requires declaring a constant. Alternatively, both versions could be provided, like `futures::task::noop_waker()` and `futures::task::noop_waker_ref()`, but that seems to me to be API clutter for a very small benefit, whereas having the `&'static` reference available is a large reduction in boilerplate.
[Previous discussion on the tracking issue starting here](https://github.com/rust-lang/rust/issues/98286#issuecomment-1862159766)
Stabilize `slice_first_last_chunk`
This PR does a few different things based around stabilizing `slice_first_last_chunk`. They are split up so this PR can be by-commit reviewed, I can move parts to a separate PR if desired.
This feature provides a very elegant API to extract arrays from either end of a slice, such as for parsing integers from binary data.
## Stabilize `slice_first_last_chunk`
ACP: https://github.com/rust-lang/libs-team/issues/69
Implementation: https://github.com/rust-lang/rust/issues/90091
Tracking issue: https://github.com/rust-lang/rust/issues/111774
This stabilizes the functionality from https://github.com/rust-lang/rust/issues/111774:
```rust
impl [T] {
pub const fn first_chunk<const N: usize>(&self) -> Option<&[T; N]>;
pub fn first_chunk_mut<const N: usize>(&mut self) -> Option<&mut [T; N]>;
pub const fn last_chunk<const N: usize>(&self) -> Option<&[T; N]>;
pub fn last_chunk_mut<const N: usize>(&mut self) -> Option<&mut [T; N]>;
pub const fn split_first_chunk<const N: usize>(&self) -> Option<(&[T; N], &[T])>;
pub fn split_first_chunk_mut<const N: usize>(&mut self) -> Option<(&mut [T; N], &mut [T])>;
pub const fn split_last_chunk<const N: usize>(&self) -> Option<(&[T], &[T; N])>;
pub fn split_last_chunk_mut<const N: usize>(&mut self) -> Option<(&mut [T], &mut [T; N])>;
}
```
Const stabilization is included for all non-mut methods, which are blocked on `const_mut_refs`. This change includes marking the trivial function `slice_split_at_unchecked` const-stable for internal use (but not fully stable).
## Remove `split_array` slice methods
Tracking issue: https://github.com/rust-lang/rust/issues/90091
Implementation: https://github.com/rust-lang/rust/pull/83233#pullrequestreview-780315524
This PR also removes the following unstable methods from the `split_array` feature, https://github.com/rust-lang/rust/issues/90091:
```rust
impl<T> [T] {
pub fn split_array_ref<const N: usize>(&self) -> (&[T; N], &[T]);
pub fn split_array_mut<const N: usize>(&mut self) -> (&mut [T; N], &mut [T]);
pub fn rsplit_array_ref<const N: usize>(&self) -> (&[T], &[T; N]);
pub fn rsplit_array_mut<const N: usize>(&mut self) -> (&mut [T], &mut [T; N]);
}
```
This is done because discussion at #90091 and its implementation PR indicate a strong preference for nonpanicking APIs that return `Option`. The only difference between functions under the `split_array` and `slice_first_last_chunk` features is `Option` vs. panic, so remove the duplicates as part of this stabilization.
This does not affect the array methods from `split_array`. We will want to revisit these once `generic_const_exprs` is further along.
## Reverse order of return tuple for `split_last_chunk{,_mut}`
An unresolved question for #111774 is whether to return `(preceding_slice, last_chunk)` (`(&[T], &[T; N])`) or the reverse (`(&[T; N], &[T])`), from `split_last_chunk` and `split_last_chunk_mut`. It is currently implemented as `(last_chunk, preceding_slice)` which matches `split_last -> (&T, &[T])`. The first commit changes these to `(&[T], &[T; N])` for these reasons:
- More consistent with other splitting methods that return multiple values: `str::rsplit_once`, `slice::split_at{,_mut}`, `slice::align_to` all return tuples with the items in order
- More intuitive (arguably opinion, but it is consistent with other language elements like pattern matching `let [a, b, rest @ ..] ...`
- If we ever added a varidic way to obtain multiple chunks, it would likely return something in order: `.split_many_last::<(2, 4)>() -> (&[T], &[T; 2], &[T; 4])`
- It is the ordering used in the `rsplit_array` methods
I think the inconsistency with `split_last` could be acceptable in this case, since for `split_last` the scalar `&T` doesn't have any internal order to maintain with the other items.
## Unresolved questions
Do we want to reserve the same names on `[u8; N]` to avoid inference confusion? https://github.com/rust-lang/rust/pull/117561#issuecomment-1793388647
---
`slice_first_last_chunk` has only been around since early 2023, but `split_array` has been around since 2021.
`@rustbot` label -T-libs +T-libs-api -T-libs +needs-fcp
cc `@rust-lang/wg-const-eval,` `@scottmcm` who raised this topic, `@clarfonthey` implementer of `slice_first_last_chunk` `@jethrogb` implementer of `split_array`
Zulip discussion: https://rust-lang.zulipchat.com/#narrow/stream/219381-t-libs/topic/Stabilizing.20array-from-slice.20*something*.3FFixes: #111774
This stabilizes all methods under `slice_first_last_chunk`.
Additionally, it const stabilizes the non-mut functions and moves the `_mut`
functions under `const_slice_first_last_chunk`. These are blocked on
`const_mut_refs`.
As part of this change, `slice_split_at_unchecked` was marked const-stable for
internal use (but not fully stable).
Add `IntoAsyncIterator`
This introduces the `IntoAsyncIterator` trait and uses it in the desugaring of the unstable `for await` loop syntax. This is mostly added for symmetry with `Iterator` and `IntoIterator`.
r? `@compiler-errors`
cc `@rust-lang/libs-api,` `@rust-lang/wg-async`
This change consists of cherry-picking the content from the original
PR[1], which got closed due to inactivity, and applying the following
changes:
* Resolving merge conflicts (obviously)
* Linked to to_ipv4_mapped instead of to_ipv4 in the documentation (seems
more appropriate)
* Added the must_use and rustc_const_unstable attributes the original
didn't have
I think it's a reasonably useful method.
[1] https://github.com/rust-lang/rust/pull/86490
detects redundant imports that can be eliminated.
for #117772 :
In order to facilitate review and modification, split the checking code and
removing redundant imports code into two PR.
Add support for making lib features internal
We have the notion of an "internal" lang feature: a feature that is never intended to be stabilized, and using which can cause ICEs and other issues without that being considered a bug.
This extends that idea to lib features as well. It is an alternative to https://github.com/rust-lang/rust/pull/115623: instead of using an attribute to declare lib features internal, we simply do this based on the name. Everything ending in `_internals` or `_internal` is considered internal.
Then we rename `core_intrinsics` to `core_intrinsics_internal`, which fixes https://github.com/rust-lang/rust/issues/115597.
The functionality of these methods from `split_array` has been absorbed by the
`slice_first_last_chunk` feature. This only affects the methods on slices,
not those with the same name that are implemented on array types.
Also adjusts testing to reflect this change.
Remove option_payload_ptr; redundant to offset_of
The `option_payload_ptr` intrinsic is no longer required as `offset_of` supports traversing enums (#114208). This PR removes it in order to dogfood offset_of (as suggested at https://github.com/rust-lang/rust/issues/106655#issuecomment-1790907626). However, it will not build until those changes reach beta (which I think is within the next 8 days?) so I've opened it as a draft.
Add `std:#️⃣:{DefaultHasher, RandomState}` exports (needs FCP)
This implements rust-lang/libs-team#267 to move the libstd hasher types to `std::hash` where they belong, instead of `std::collections::hash_map`.
<details><summary>The below no longer applies, but is kept for clarity.</summary>
This is a small refactor for #27242, which moves the definitions of `RandomState` and `DefaultHasher` into `std::hash`, but in a way that won't be noticed in the public API.
I've opened rust-lang/libs-team#267 as a formal ACP to move these directly into the root of `std::hash`, but for now, they're at least separated out from the collections code in a way that will make moving that around easier.
I decided to simply copy the rustdoc for `std::hash` from `core::hash` since I think it would be ideal for the two to diverge longer-term, especially if the ACP is accepted. However, I would be willing to factor them out into a common markdown document if that's preferred.
</details>
Stabilize `const_maybe_uninit_zeroed` and `const_mem_zeroed`
Make `MaybeUninit::zeroed` and `mem::zeroed` const stable. Newly stable API:
```rust
// core::mem
pub const unsafe fn zeroed<T>() ->;
impl<T> MaybeUninit<T> {
pub const fn zeroed() -> MaybeUninit<T>;
}
```
This relies on features based around `const_mut_refs`. Per `@RalfJung,` this should be OK since we do not leak any `&mut` to the user.
For this to be possible, intrinsics `assert_zero_valid` and `assert_mem_uninitialized_valid` were made const stable.
Tracking issue: #91850
Zulip discussion: https://rust-lang.zulipchat.com/#narrow/stream/146212-t-compiler.2Fconst-eval/topic/.60const_mut_refs.60.20dependents
r? libs-api
`@rustbot` label -T-libs +T-libs-api +A-const-eval
cc `@RalfJung` `@oli-obk` `@rust-lang/wg-const-eval`
Make `MaybeUninit::zeroed` const stable. Newly stable API:
// core::mem
impl<T> MaybeUninit<T> {
pub const fn zeroed() -> MaybeUninit<T>;
}
Use of `const_mut_refs` should be acceptable since we do not leak the
mutability.
Tracking issue: #91850
Derive `Ord`, `PartialOrd` and `Hash` for `SocketAddr*`
Fixes#116711
The main pain of this PR is to fix the buggy impl of `Ord` for `SocketAddrV6`, which ignored half of the fields (while `PartialEq` is derived):
4603f0b8af/library/core/src/net/socket_addr.rs (L99-L106)4603f0b8af/library/core/src/net/socket_addr.rs (L676)
For me it looks like a simple copy-paste error made in https://github.com/rust-lang/rust/pull/72239 (copy from v4 impl) (cc `@hch12907),` as I don't see this behavior being mentioned anywhere on the PR and it also does not respect `cmp` trait "rules". I also do not see any reasons for those impls to _not_ be derived.
It's a shame we did not notice this for 28 versions/3 years. I guess this is a bug fix, but I'm not sure what the process here should be.
r? libs
optimize zipping over array iterators
Fixes#115339 (somewhat)
the new assembly:
```asm
zip_arrays:
.cfi_startproc
vmovups (%rdx), %ymm0
leaq 32(%rsi), %rcx
vxorps %xmm1, %xmm1, %xmm1
vmovups %xmm1, -24(%rsp)
movq $0, -8(%rsp)
movq %rsi, -88(%rsp)
movq %rdi, %rax
movq %rcx, -80(%rsp)
vmovups %ymm0, -72(%rsp)
movq $0, -40(%rsp)
movq $32, -32(%rsp)
movq -24(%rsp), %rcx
vmovups (%rsi,%rcx), %ymm0
vorps -72(%rsp,%rcx), %ymm0, %ymm0
vmovups %ymm0, (%rsi,%rcx)
vmovups (%rsi), %ymm0
vmovups %ymm0, (%rdi)
vzeroupper
retq
```
This is still longer than the slice version given in the issue but at least it eliminates the terrible `vpextrb`/`orb` chain. I guess this is due to excessive memcpys again (haven't looked at the llvmir)?
The `TrustedLen` specialization is a drive-by change since I had to do something for the default impl anyway to be able to specialize the `TrustedRandomAccessNoCoerce` impl.
Implement `slice::split_once` and `slice::rsplit_once`
Feature gate is `slice_split_once` and tracking issue is #112811. These are equivalents to the existing `str::split_once` and `str::rsplit_once` methods.
Add "integer square root" method to integer primitive types
For every suffix `N` among `8`, `16`, `32`, `64`, `128` and `size`, this PR adds the methods
```rust
const fn uN::isqrt() -> uN;
const fn iN::isqrt() -> iN;
const fn iN::checked_isqrt() -> Option<iN>;
```
to compute the [integer square root](https://en.wikipedia.org/wiki/Integer_square_root), addressing issue #89273.
The implementation is based on the [base 2 digit-by-digit algorithm](https://en.wikipedia.org/wiki/Methods_of_computing_square_roots#Binary_numeral_system_(base_2)) on Wikipedia, which after some benchmarking has proved to be faster than both binary search and Heron's/Newton's method. I haven't had the time to understand and port [this code](http://atoms.alife.co.uk/sqrt/SquareRoot.java) based on lookup tables instead, but I'm not sure whether it's worth complicating such a function this much for relatively little benefit.
Implement Step for ascii::Char
This allows iterating over ranges of `ascii::Char`, similarly to ranges of `char`.
Note that `ascii::Char` is still unstable, tracked in #110998.
Fix implementation of `Duration::checked_div`
I ran across this while running some sanity checks on `time`. Quickcheck immediately found a bug, and as I'd modified the code from `std` I knew there was a bug here as well.
tl;dr this code fails ([playground](https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=1189a3efcdfc192c27d6d87815359353))
```rust
use std::time::Duration;
fn main() {
assert_eq!(
Duration::new(1, 1).checked_div(7),
Some(Duration::new(0, 142_857_143)),
);
}
```
The existing code determines that 1/7 = 0 (seconds), 1/7 = 0 (nanoseconds), 1 billion / 7 = 142,857,142 (extra nanoseconds). The billion comes from multiplying the remainder of the seconds (1) by the number of nanoseconds in a second. However, **this wrongly ignores any remaining nanoseconds**. This PR takes that into consideration, adds a test, and also changes the roundabout way of calculating the remainder into directly computing it.
Note: This is _not_ a rounding error. This result divides evenly.
`@rustbot` label +A-time +C-bug +S-waiting-on-reviewer +T-libs
core/any: remove Provider trait, rename Demand to Request
This touches on two WIP features:
* `error_generic_member_access`
* tracking issue: https://github.com/rust-lang/rust/issues/99301
* RFC (WIP): https://github.com/rust-lang/rfcs/pull/2895
* `provide_any`
* tracking issue: https://github.com/rust-lang/rust/issues/96024
* RFC: https://github.com/rust-lang/rfcs/pull/3192
The changes in this PR are intended to address libs meeting feedback summarized by `@Amanieu` in https://github.com/rust-lang/rust/issues/96024#issuecomment-1554773172
The specific items this PR addresses so far are:
> We feel that the names "demand" and "request" are somewhat synonymous and would like only one of those to be used for better consistency.
I went with `Request` here since it sounds nicer, but I'm mildly concerned that at first glance it could be confused with the use of the word in networking context.
> The Provider trait should be deleted and its functionality should be merged into Error. We are happy to only provide an API that is only usable with Error. If there is demand for other uses then this can be provided through an external crate.
The net impact this PR has is that examples which previously looked like
```
core::any::request_ref::<String>(&err).unwramp()
```
now look like
```
(&err as &dyn core::error::Error).request_value::<String>().unwrap()
```
These are methods that based on the type hint when called return an `Option<T>` of that type. I'll admit I don't fully understand how that's done, but it involves `core::any::tags::Type` and `core::any::TaggedOption`, neither of which are exposed in the public API, to construct a `Request` which is then passed to the `Error.provide` method.
Something that I'm curious about is whether or not they are essential to the use of `Request` types (prior to this PR referred to as `Demand`) and if so does the fact that they are kept private imply that `Request`s are only meant to be constructed privately within the standard library? That's what it looks like to me.
These methods ultimately call into code that looks like:
```
/// Request a specific value by tag from the `Error`.
fn request_by_type_tag<'a, I>(err: &'a (impl Error + ?Sized)) -> Option<I::Reified>
where
I: tags::Type<'a>,
{
let mut tagged = core::any::TaggedOption::<'a, I>(None);
err.provide(tagged.as_request());
tagged.0
}
```
As far as the `Request` API is concerned, one suggestion I would like to make is that the previous example should look more like this:
```
/// Request a specific value by tag from the `Error`.
fn request_by_type_tag<'a, I>(err: &'a (impl Error + ?Sized)) -> Option<I::Reified>
where
I: tags::Type<'a>,
{
let tagged_request = core::any::Request<I>::new_tagged();
err.provide(tagged_request);
tagged.0
}
```
This makes it possible for anyone to construct a `Request` for use in their own projects without exposing an implementation detail like `TaggedOption` in the API surface.
Otherwise noteworthy is that I had to add `pub(crate)` on both `core::any::TaggedOption` and `core::any::tags` since `Request`s now need to be constructed in the `core::error` module. I considered moving `TaggedOption` into the `core::error` module but again I figured it's an implementation detail of `Request` and belongs closer to that.
At the time I am opening this PR, I have not yet looked into the following bit of feedback:
> We took a look at the generated code and found that LLVM is unable to optimize multiple .provide_* calls into a switch table because each call fetches the type id from Erased::type_id separately each time and the compiler doesn't know that these calls all return the same value. This should be fixed.
This is what I'll focus on next while waiting for feedback on the progress so far. I suspect that learning more about the type IDs will help me understand the need for `TaggedOption` a little better.
* remove `impl Provider for Error`
* rename `Demand` to `Request`
* update docstrings to focus on the conceptual API provided by `Request`
* move `core::any::{request_ref, request_value}` functions into `core::error`
* move `core::any::tag`, `core::any::Request`, an `core::any::TaggedOption` into `core::error`
* replace `provide_any` feature name w/ `error_generic_member_access`
* move `core::error::request_{ref,value} tests into core::tests::error module
* update unit and doc tests
This is inherited from the old PR.
This method returns an iterator over mapped windows of the starting
iterator. Adding the more straight-forward `Iterator::windows` is not
easily possible right now as the items are stored in the iterator type,
meaning the `next` call would return references to `self`. This is not
allowed by the current `Iterator` trait design. This might change once
GATs have landed.
The idea has been brought up by @m-ou-se here:
https://rust-lang.zulipchat.com/#narrow/stream/219381-t-libs/topic/Iterator.3A.3A.7Bpairwise.2C.20windows.7D/near/224587771
Co-authored-by: Lukas Kalbertodt <lukas.kalbertodt@gmail.com>
Specialize `StepBy<Range<{integer}>>`
OLD
iter::bench_range_step_by_fold_u16 700.00ns/iter +/- 10.00ns
iter::bench_range_step_by_fold_usize 519.00ns/iter +/- 6.00ns
iter::bench_range_step_by_loop_u32 555.00ns/iter +/- 7.00ns
iter::bench_range_step_by_sum_reducible 37.00ns/iter +/- 0.00ns
NEW
iter::bench_range_step_by_fold_u16 49.00ns/iter +/- 0.00ns
iter::bench_range_step_by_fold_usize 194.00ns/iter +/- 1.00ns
iter::bench_range_step_by_loop_u32 98.00ns/iter +/- 0.00ns
iter::bench_range_step_by_sum_reducible 1.00ns/iter +/- 0.00ns
NEW + `-Ctarget-cpu=x86-64-v3`
iter::bench_range_step_by_fold_u16 22.00ns/iter +/- 0.00ns
iter::bench_range_step_by_fold_usize 80.00ns/iter +/- 1.00ns
iter::bench_range_step_by_loop_u32 41.00ns/iter +/- 0.00ns
iter::bench_range_step_by_sum_reducible 1.00ns/iter +/- 0.00ns
I have only optimized for walltime of those methods, I haven't tested whether it eliminates bounds checks when indexing into slices via things like `(0..slice.len()).step_by(16)`.
For ranges < usize we determine the number of items
StepBy would yield and then store that in the range.end
instead of the actual end. This significantly
simplifies calculation of the loop induction variable
especially in cases where StepBy::step (an usize)
could overflow the Range's item type
Ignore `core`, `alloc` and `test` tests that require unwinding on `-C panic=abort`
Some of the tests for `core` and `alloc` require unwinding through their use of `catch_unwind`. These tests fail when testing using `-C panic=abort` (in my case through a target without unwinding support, and `-Z panic-abort-tests`), while they should be ignored as they don't indicate a failure.
This PR marks all of these tests with this attribute:
```rust
#[cfg_attr(not(panic = "unwind"), ignore = "test requires unwinding support")]
```
I'm not aware of a way to test this on rust-lang/rust's CI, as we don't test any target with `-C panic=abort`, but I tested this locally on a Ferrocene target and it does indeed make the test suite pass.
* ensuring that offset_of!(Self, ...) works iff inside an impl block
* ensuring that the output type is usize and doesn't coerce. this can be
changed in the future, but if it is done, it should be a conscious descision
* improving the privacy checking test
* ensuring that generics don't let you escape the unsized check
Add midpoint function for all integers and floating numbers
This pull-request adds the `midpoint` function to `{u,i}{8,16,32,64,128,size}`, `NonZeroU{8,16,32,64,size}` and `f{32,64}`.
This new function is analog to the [C++ midpoint](https://en.cppreference.com/w/cpp/numeric/midpoint) function, and basically compute `(a + b) / 2` with a rounding towards ~~`a`~~ negative infinity in the case of integers. Or simply said: `midpoint(a, b)` is `(a + b) >> 1` as if it were performed in a sufficiently-large signed integral type.
Note that unlike the C++ function this pull-request does not implement this function on pointers (`*const T` or `*mut T`). This could be implemented in a future pull-request if desire.
### Implementation
For `f32` and `f64` the implementation in based on the `libcxx` [one](18ab892ff7/libcxx/include/__numeric/midpoint.h (L65-L77)). I originally tried many different approach but all of them failed or lead me with a poor version of the `libcxx`. Note that `libstdc++` has a very similar one; Microsoft STL implementation is also basically the same as `libcxx`. It unfortunately doesn't seems like a better way exist.
For unsigned integers I created the macro `midpoint_impl!`, this macro has two branches:
- The first one take `$SelfT` and is used when there is no unsigned integer with at least the double of bits. The code simply use this formula `a + (b - a) / 2` with the arguments in the correct order and signs to have the good rounding.
- The second branch is used when a `$WideT` (at least double of bits as `$SelfT`) is provided, using a wider number means that no overflow can occur, this greatly improve the codegen (no branch and less instructions).
For signed integers the code basically forwards the signed numbers to the unsigned version of midpoint by mapping the signed numbers to their unsigned numbers (`ex: i8 [-128; 127] to [0; 255]`) and vice versa.
I originally created a version that worked directly on the signed numbers but the code was "ugly" and not understandable. Despite this mapping "overhead" the codegen is better than my most optimized version on signed integers.
~~Note that in the case of unsigned numbers I tried to be smart and used `#[cfg(target_pointer_width = "64")]` to determine if using the wide version was better or not by looking at the assembly on godbolt. This was applied to `u32`, `u64` and `usize` and doesn't change the behavior only the assembly code generated.~~
Spelling library
Split per https://github.com/rust-lang/rust/pull/110392
I can squash once people are happy w/ the changes. It's really uncommon for large sets of changes to be perfectly acceptable w/o at least some changes.
I probably won't have time to respond until tomorrow or the next day
