Slight perf improvement on char::to_ascii_lowercase
`char::to_ascii_lowercase()` was checking if it was ascii and then if it was in the right range. Instead propose to check once (I think removing a compare and a shift in the process: [godbolt](https://godbolt.org/z/e5Tora) ).
before:
```
test char::methods::bench_to_ascii_lowercase ... bench: 11,196 ns/iter (+/- 632)
test char::methods::bench_to_ascii_uppercase ... bench: 11,656 ns/iter (+/- 671)
```
after:
```
test char::methods::bench_to_ascii_lowercase ... bench: 9,612 ns/iter (+/- 979)
test char::methods::bench_to_ascii_uppercase ... bench: 8,241 ns/iter (+/- 701)
```
(calling u8::to_ascii_lowercase and letting that flip the 5th bit is also an option, but it's more instructions. I'm thinking for things around ascii and char we want to be as efficient as possible.)
simplify eat_digits
Simplify eat_digits by checking values in iterator, plus decrease function size, by returning unchecked slices.
https://godbolt.org/z/cxjav4
Bump stabilization version for const int methods
These methods missed the beta cutoff. See #80962 for details.
`@rustbot` modify labels to +A-const-fn, +A-intrinsics
r? `@m-ou-se`
Stabilize remaining integer methods as `const fn`
This pull request stabilizes the following methods as `const fn`:
- `i*::checked_div`
- `i*::checked_div_euclid`
- `i*::checked_rem`
- `i*::checked_rem_euclid`
- `i*::div_euclid`
- `i*::overflowing_div`
- `i*::overflowing_div_euclid`
- `i*::overflowing_rem`
- `i*::overflowing_rem_euclid`
- `i*::rem_euclid`
- `i*::wrapping_div`
- `i*::wrapping_div_euclid`
- `i*::wrapping_rem`
- `i*::wrapping_rem_euclid`
- `u*::checked_div`
- `u*::checked_div_euclid`
- `u*::checked_rem`
- `u*::checked_rem_euclid`
- `u*::div_euclid`
- `u*::overflowing_div`
- `u*::overflowing_div_euclid`
- `u*::overflowing_rem`
- `u*::overflowing_rem_euclid`
- `u*::rem_euclid`
- `u*::wrapping_div`
- `u*::wrapping_div_euclid`
- `u*::wrapping_rem`
- `u*::wrapping_rem_euclid`
These can all be implemented on the current stable (1.49). There are two unstable details: const likely/unlikely and unchecked division/remainder. Both of these are for optimizations, and are in no way required to make the methods function; there is no exposure of these details publicly. Per comments below, it seems best practice is to stabilize the intrinsics. As such, `intrinsics::unchecked_div` and `intrinsics::unchecked_rem` have been stabilized as `const` as part of this pull request as well. The methods themselves remain unstable.
I believe part of the reason these were not stabilized previously was the behavior around division by 0 and modulo 0. After testing on nightly, the diagnostic for something like `const _: i8 = 5i8 % 0i8;` is similar to that of `const _: i8 = 5i8.rem_euclid(0i8);` (assuming the appropriate feature flag is enabled). As such, I believe these methods are ready to be stabilized as `const fn`.
This pull request represents the final methods mentioned in #53718. As such, this PR closes#53718.
`@rustbot` modify labels to +A-const-fn, +T-libs
Stabilize `unsigned_abs`
Resolves#74913.
This PR stabilizes the `i*::unsigned_abs()` method, which returns the absolute value of an integer _as its unsigned equivalent_. This has the advantage that it does not overflow on `i*::MIN`.
I have gone ahead and used this in a couple locations throughout the repository.
Add `impl Div<NonZeroU{0}> for u{0}` which cannot panic
Dividing an unsigned int by a `NonZeroUxx` requires a user to write (for example, in [this SO question](https://stackoverflow.com/questions/64855738/how-to-inform-the-optimizer-that-nonzerou32get-will-never-return-zero)):
```
pub fn safe_div(x: u32, y: std::num::NonZeroU32) -> u32 {
x / y.get()
}
```
which generates a panicking-checked-div [assembly](https://godbolt.org/#g:!((g:!((g:!((h:codeEditor,i:(fontScale:14,j:1,lang:rust,selection:(endColumn:2,endLineNumber:6,positionColumn:2,positionLineNumber:6,selectionStartColumn:2,selectionStartLineNumber:6,startColumn:2,startLineNumber:6),source:%27pub+fn+div(x:+u32,+y:+u32)+-%3E+u32+%7B%0A++++x+/+y%0A%7D%0Apub+fn+safe_div(x:+u32,+y:+std::num::NonZeroU32)+-%3E+u32+%7B%0A++++x+/+y.get()+//+an+unchecked+division+expected%0A%7D%27),l:%275%27,n:%270%27,o:%27Rust+source+%231%27,t:%270%27)),k:50,l:%274%27,n:%270%27,o:%27%27,s:0,t:%270%27),(g:!((h:compiler,i:(compiler:r1470,filters:(b:%270%27,binary:%271%27,commentOnly:%270%27,demangle:%270%27,directives:%270%27,execute:%271%27,intel:%270%27,libraryCode:%271%27,trim:%271%27),fontScale:14,j:1,lang:rust,libs:!(),options:%27-O%27,selection:(endColumn:1,endLineNumber:1,positionColumn:1,positionLineNumber:1,selectionStartColumn:1,selectionStartLineNumber:1,startColumn:1,startLineNumber:1),source:1),l:%275%27,n:%270%27,o:%27rustc+1.47.0+(Editor+%231,+Compiler+%231)+Rust%27,t:%270%27)),k:50,l:%274%27,n:%270%27,o:%27%27,s:0,t:%270%27)),l:%272%27,n:%270%27,o:%27%27,t:%270%27)),version:4).
Avoiding the `panic` currently requires `unsafe` code.
This PR adds an `impl Div<NonZeroU{0}> for u{0}` (and `impl Rem<NonZeroU{0}> for u{0}`) which calls the `unchecked_div` (and `unchecked_rem`) intrinsic without any additional checks,
making the following code compile:
```
pub fn safe_div(x: u32, y: std::num::NonZeroU32) -> u32 {
x / y
}
pub fn safe_rem(x: u32, y: std::num::NonZeroU32) -> u32 {
x % y
}
```
The doc is set to match the regular div impl [docs](https://doc.rust-lang.org/beta/src/core/ops/arith.rs.html#460).
I've marked these as stable because (as I understand it) trait impls are automatically stable. I'm happy to change it to unstable if needed.
Following `@dtolnay` template from a similar issue:
this adds the following **stable** impls, which rely on dividing unsigned integers by nonzero integers being well defined and previously would have involved unsafe code to encode that knowledge:
```
impl Div<NonZeroU8> for u8 {
type Output = u8;
}
impl Rem<NonZeroU8> for u8 {
type Output = u8;
}
```
and equivalent for u16, u32, u64, u128, usize, but **not** for i8, i16, i32, i64, i128, isize (since -1/MIN is undefined).
r? `@dtolnay`
Move {f32,f64}::clamp to core.
`clamp` was recently stabilized (tracking issue: https://github.com/rust-lang/rust/issues/44095). But although `Ord::clamp` was added in `core` (because `Ord` is in `core`), the versions for the `f32` and `f64` primitives were added in `std` (together with `floor`, `sin`, etc.), not in `core` (together with `min`, `max`, `from_bits`, etc.).
This change moves them to `core`, such that `clamp` on floats is available in `no_std` programs as well.
Integer types have a `count_ones` method that end up calling
`intrinsics::ctpop`.
On some architectures, that intrinsic is translated as a corresponding
CPU instruction know as "popcount" or "popcnt".
This PR makes it so that searching for those names in rustdoc shows those methods.
CC https://blog.rust-lang.org/2020/11/19/Rust-1.48.html#adding-search-aliases
Also stabilize constctlz for const ctlz_nonzero.
The public methods stabilized const by this commit are:
* `{i*,u*}::checked_pow`
* `{i*,u*}::saturating_pow`
* `{i*,u*}::wrapping_pow`
* `{i*,u*}::overflowing_pow`
* `{i*,u*}::pow`
* `u*::next_power_of_two`
* `u*::checked_next_power_of_two`
* `u*::wrapping_next_power_of_two` (the method itself is still unstable)
Refactor IntErrorKind to avoid "underflow" terminology
This PR is a continuation of #76455
# Changes
- `Overflow` renamed to `PosOverflow` and `Underflow` renamed to `NegOverflow` after discussion in #76455
- Changed some of the parsing code to return `InvalidDigit` rather than `Empty` for strings "+" and "-". https://users.rust-lang.org/t/misleading-error-in-str-parse-for-int-types/49178
- Carry the problem `char` with the `InvalidDigit` variant.
- Necessary changes were made to the compiler as it depends on `int_error_matching`.
- Redid tests to match on specific errors.
r? ```@KodrAus```
Point out that total_cmp is no strict superset of partial comparison
Partial comparison and total_cmp are not equal. This helps
preventing the mistake of creating float wrappers that
base their Ord impl on total_cmp and their PartialOrd impl on
the PartialOrd impl of the float type. PartialOrd and Ord
[are required to agree with each other](https://doc.rust-lang.org/std/cmp/trait.Ord.html#how-can-i-implement-ord).
Partial comparison and total_cmp are not equal. This helps
preventing the mistake of creating float wrappers that
base their Ord impl on total_cmp and their PartialOrd impl on
the PartialOrd impl of the float type. PartialOrd and Ord
are required to agree with each other.
