Make overflowing and wrapping negation const #58044

Lokathor · 2019-02-01T08:36:30Z

Remember that the signed and unsigned versions are slightly different here, so there's four functions made const instead of just two.

Lokathor · 2019-02-01T08:37:18Z

PR based on #57536 seeming to sit around for a bit without objection

Mark-Simulacrum · 2019-02-01T13:04:59Z

r? @oli-obk

oli-obk · 2019-02-01T13:36:07Z

Please update the tests for these function to make them check the const eval result against the runtime result. Preexisting examples of such tests are in

rust/src/test/run-pass/const-int-wrapping.rs

Line 14 in 0c91f3d

const SHR_B: u32 = 128u32.wrapping_shr(128);

src/libcore/num/mod.rs

Lokathor · 2019-02-02T01:57:32Z

Tests added. I used the playground to set the test input/output values using current stable so it's a "double check" that the new formulas haven't changed the math at all.

oli-obk · 2019-02-03T11:48:38Z

r? @Centril impl lgtm now, but I don't know what the rules for insta-stable constification are

Centril · 2019-02-03T13:44:44Z

@oli-obk Since this is something that doesn't require feature gates, intrinsics, etc., someone from the libs team needs to fcp... for that, r? @SimonSapin

kennytm · 2019-02-08T04:38:29Z

You don't need to insta-stable the const. See the #[rustc_const_unstable] attribute.

rfcbot · 2019-02-19T18:17:00Z

🔔 This is now entering its final comment period, as per the review above. 🔔

alexcrichton · 2019-02-19T19:44:50Z

@bors: r+

bors · 2019-02-19T19:44:51Z

📌 Commit e06302f has been approved by alexcrichton

Make overflowing and wrapping negation const Remember that the signed and unsigned versions are slightly different here, so there's four functions made const instead of just two.

Rollup of 24 pull requests Successful merges: - #56470 (Modify doctest's auto-`fn main()` to allow `Result`s) - #58044 (Make overflowing and wrapping negation const) - #58303 (Improve stability tags display) - #58336 (Fix search results interactions) - #58384 (Fix tables display) - #58392 (Use less explicit shifting in std::net::ip) - #58409 (rustdoc: respect alternate flag when formatting impl trait) - #58456 (Remove no longer accurate diagnostic code about NLL) - #58528 (Don't use an allocation for ItemId in StmtKind) - #58530 (Monomorphize less code in fs::{read|write}) - #58534 (Mention capping forbid lints) - #58536 (Remove UB in pointer tests) - #58538 (Add missing fmt structs examples) - #58539 (Add alias methods to PathBuf for underlying OsString (#58234)) - #58544 (Fix doc for rustc "-g" flag) - #58545 (Add regression test for a specialization-related ICE (#39448)) - #58546 (librustc_codegen_llvm => 2018) - #58551 (Explain a panic in test case net::tcp::tests::double_bind) - #58553 (Use more impl header lifetime elision) - #58562 (Fix style nits) - #58565 (Fix typo in std::future::Future docs) - #58568 (Fix a transposition in driver.rs.) - #58569 (Reduce Some Code Repetitions like `(n << amt) >> amt`) - #58576 (Stabilize iter::successors and iter::from_fn)

Pkgsrc changes: * Bump required rust version to build to 1.33.0. * Adapt patches to changed file locations. * (I worry about 32-bit ports, now that Atomic64 apparently is First-Class; this has been built on NetBSD/amd64 so far) Upstream changes: Version 1.34.0 (2019-04-11) ========================== Language -------- - [You can now use `#[deprecated = "reason"]`][58166] as a shorthand for `#[deprecated(note = "reason")]`. This was previously allowed by mistake but had no effect. - [You can now accept token streams in `#[attr()]`,`#[attr[]]`, and `#[attr{}]` procedural macros.][57367] - [You can now write `extern crate self as foo;`][57407] to import your crate's root into the extern prelude. Compiler -------- - [You can now target `riscv64imac-unknown-none-elf` and `riscv64gc-unknown-none-elf`.][58406] - [You can now enable linker plugin LTO optimisations with `-C linker-plugin-lto`.][58057] This allows rustc to compile your Rust code into LLVM bitcode allowing LLVM to perform LTO optimisations across C/C++ FFI boundaries. - [You can now target `powerpc64-unknown-freebsd`.][57809] Libraries --------- - [The trait bounds have been removed on some of `HashMap<K, V, S>`'s and `HashSet<T, S>`'s basic methods.][58370] Most notably you no longer require the `Hash` trait to create an iterator. - [The `Ord` trait bounds have been removed on some of `BinaryHeap<T>`'s basic methods.][58421] Most notably you no longer require the `Ord` trait to create an iterator. - [The methods `overflowing_neg` and `wrapping_neg` are now `const` functions for all numeric types.][58044] - [Indexing a `str` is now generic over all types that implement `SliceIndex<str>`.][57604] - [`str::trim`, `str::trim_matches`, `str::trim_{start, end}`, and `str::trim_{start, end}_matches` are now `#[must_use]`][57106] and will produce a warning if their returning type is unused. - [The methods `checked_pow`, `saturating_pow`, `wrapping_pow`, and `overflowing_pow` are now available for all numeric types.][57873] These are equivalvent to methods such as `wrapping_add` for the `pow` operation. Stabilized APIs --------------- #### std & core * [`Any::type_id`] * [`Error::type_id`] * [`atomic::AtomicI16`] * [`atomic::AtomicI32`] * [`atomic::AtomicI64`] * [`atomic::AtomicI8`] * [`atomic::AtomicU16`] * [`atomic::AtomicU32`] * [`atomic::AtomicU64`] * [`atomic::AtomicU8`] * [`convert::Infallible`] * [`convert::TryFrom`] * [`convert::TryInto`] * [`iter::from_fn`] * [`iter::successors`] * [`num::NonZeroI128`] * [`num::NonZeroI16`] * [`num::NonZeroI32`] * [`num::NonZeroI64`] * [`num::NonZeroI8`] * [`num::NonZeroIsize`] * [`slice::sort_by_cached_key`] * [`str::escape_debug`] * [`str::escape_default`] * [`str::escape_unicode`] * [`str::split_ascii_whitespace`] #### std * [`Instant::checked_add`] * [`Instant::checked_sub`] * [`SystemTime::checked_add`] * [`SystemTime::checked_sub`] Cargo ----- - [You can now use alternative registries to crates.io.][cargo/6654] Misc ---- - [You can now use the `?` operator in your documentation tests without manually adding `fn main() -> Result<(), _> {}`.][56470] Compatibility Notes ------------------- - [`Command::before_exec` is now deprecated in favor of the unsafe method `Command::pre_exec`.][58059] - [Use of `ATOMIC_{BOOL, ISIZE, USIZE}_INIT` is now deprecated.][57425] As you can now use `const` functions in `static` variables. [58370]: rust-lang/rust#58370 [58406]: rust-lang/rust#58406 [58421]: rust-lang/rust#58421 [58166]: rust-lang/rust#58166 [58044]: rust-lang/rust#58044 [58057]: rust-lang/rust#58057 [58059]: rust-lang/rust#58059 [57809]: rust-lang/rust#57809 [57873]: rust-lang/rust#57873 [57604]: rust-lang/rust#57604 [57367]: rust-lang/rust#57367 [57407]: rust-lang/rust#57407 [57425]: rust-lang/rust#57425 [57106]: rust-lang/rust#57106 [56470]: rust-lang/rust#56470 [cargo/6654]: rust-lang/cargo#6654 [`Any::type_id`]: https://doc.rust-lang.org/std/any/trait.Any.html#tymethod.type_id [`Error::type_id`]: https://doc.rust-lang.org/std/error/trait.Error.html#tymethod.type_id [`atomic::AtomicI16`]: https://doc.rust-lang.org/std/atomic/struct.AtomicI16.html [`atomic::AtomicI32`]: https://doc.rust-lang.org/std/atomic/struct.AtomicI32.html [`atomic::AtomicI64`]: https://doc.rust-lang.org/std/atomic/struct.AtomicI64.html [`atomic::AtomicI8`]: https://doc.rust-lang.org/std/atomic/struct.AtomicI8.html [`atomic::AtomicU16`]: https://doc.rust-lang.org/std/atomic/struct.AtomicU16.html [`atomic::AtomicU32`]: https://doc.rust-lang.org/std/atomic/struct.AtomicU32.html [`atomic::AtomicU64`]: https://doc.rust-lang.org/std/atomic/struct.AtomicU64.html [`atomic::AtomicU8`]: https://doc.rust-lang.org/std/atomic/struct.AtomicU8.html [`convert::Infallible`]: https://doc.rust-lang.org/std/convert/enum.Infallible.html [`convert::TryFrom`]: https://doc.rust-lang.org/std/convert/trait.TryFrom.html [`convert::TryInto`]: https://doc.rust-lang.org/std/convert/trait.TryInto.html [`iter::from_fn`]: https://doc.rust-lang.org/std/iter/fn.from_fn.html [`iter::successors`]: https://doc.rust-lang.org/std/iter/fn.successors.html [`num::NonZeroI128`]: https://doc.rust-lang.org/std/num/struct.NonZeroI128.html [`num::NonZeroI16`]: https://doc.rust-lang.org/std/num/struct.NonZeroI16.html [`num::NonZeroI32`]: https://doc.rust-lang.org/std/num/struct.NonZeroI32.html [`num::NonZeroI64`]: https://doc.rust-lang.org/std/num/struct.NonZeroI64.html [`num::NonZeroI8`]: https://doc.rust-lang.org/std/num/struct.NonZeroI8.html [`num::NonZeroIsize`]: https://doc.rust-lang.org/std/num/struct.NonZeroIsize.html [`slice::sort_by_cached_key`]: https://doc.rust-lang.org/std/slice/fn.sort_by_cached_key [`str::escape_debug`]: https://doc.rust-lang.org/std/primitive.str.html#method.escape_debug [`str::escape_default`]: https://doc.rust-lang.org/std/primitive.str.html#method.escape_default [`str::escape_unicode`]: https://doc.rust-lang.org/std/primitive.str.html#method.escape_unicode [`str::split_ascii_whitespace`]: https://doc.rust-lang.org/std/primitive.str.html#method.split_ascii_whitespace [`Instant::checked_add`]: https://doc.rust-lang.org/std/time/struct.Instant.html#method.checked_add [`Instant::checked_sub`]: https://doc.rust-lang.org/std/time/struct.Instant.html#method.checked_sub [`SystemTime::checked_add`]: https://doc.rust-lang.org/std/time/struct.SystemTime.html#method.checked_add [`SystemTime::checked_sub`]: https://doc.rust-lang.org/std/time/struct.SystemTime.html#method.checked_sub

Make `abs`, `wrapping_abs`, `overflowing_abs` const functions This makes `abs`, `wrapping_abs` and `overflowing_abs` const functions like rust-lang#58044 makes `wrapping_neg` and `overflowing_neg` const functions. `abs` is made const by returning `(self ^ -1) - -1` = `!self + 1` = `-self` for negative numbers and `(self ^ 0) - 0` = `self` for non-negative numbers. The subexpression `self >> ($BITS - 1)` evaluates to `-1` for negative numbers and `0` otherwise. The subtraction overflows when `self` is `min_value()`, as we would be subtracting `max_value() - -1`; this is when `abs` should overflow. `wrapping_abs` and `overflowing_abs` make use of `wrapping_sub` and `overflowing_sub` instead of the subtraction operator.

@oli-obk

Clean up const-hack PRs now that const if / match exist. Closes rust-lang#67627. Cleans up these merged PRs tagged with `const-hack`: - rust-lang#63810 - rust-lang#63786 - rust-lang#61635 - rust-lang#58044 reverting their contents to have the match or if expressions they originally contained. r? @oli-obk There's one more PR in those tagged with `const-hack` that originally wasn't merged (rust-lang#65107). Reading the thread, it looks like it was originally closed because the `const-hack` for the checked arithmetic non-negligibly hurt performance, and because there was no way to manipulate the returned Option at compile time anyway (with neither const if nor const match). Would you like me to add these changes to the changes from this PR here too, now that we have the necessary features?

Make overflowing and wrapping negation const

2f5d245

Remember that the signed and unsigned versions are slightly different here, so there's four functions made const instead of just two.

rust-highfive assigned Mark-Simulacrum Feb 1, 2019

This comment has been minimized.

Sign in to view

rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Feb 1, 2019

This comment has been minimized.

Sign in to view

Don't know why I wasn't using self properly there

26a3540

rust-highfive assigned oli-obk and unassigned Mark-Simulacrum Feb 1, 2019

nagisa reviewed Feb 1, 2019

View reviewed changes

src/libcore/num/mod.rs Outdated Show resolved Hide resolved

Centril added needs-fcp This change is insta-stable, so needs a completed FCP to proceed. T-libs-api Relevant to the library API team, which will review and decide on the PR/issue. relnotes Marks issues that should be documented in the release notes of the next release. labels Feb 1, 2019

Lokathor added 3 commits February 1, 2019 18:43

Simplify the overflowing_neg expression

481b354

const-int-overflowing.rs += overflowing_neg

5256efb

const-int-wrapping.rs += wrapping_neg

31bf7e1

This comment has been minimized.

Sign in to view

fix the build errors

e06302f

rust-highfive assigned Centril and unassigned oli-obk Feb 3, 2019

rust-highfive assigned SimonSapin and unassigned Centril Feb 3, 2019

kennytm added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Feb 8, 2019

bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-team Status: Awaiting decision from the relevant subteam (see the T-<team> label). labels Feb 19, 2019

kennytm mentioned this pull request Feb 20, 2019

Rollup of 24 pull requests #58578

Merged

bors merged commit e06302f into rust-lang:master Feb 20, 2019

rfcbot added finished-final-comment-period The final comment period is finished for this PR / Issue. and removed final-comment-period In the final comment period and will be merged soon unless new substantive objections are raised. labels Mar 1, 2019

Centril mentioned this pull request Mar 28, 2019

Make wrapping_neg and overflowing_neg functions into const #57536

Closed

Centril added this to the 1.34 milestone Apr 26, 2019

mjbshaw mentioned this pull request Jul 6, 2019

Tracking Issue for more const int functions #53718

Closed

59 tasks

tspiteri mentioned this pull request Aug 21, 2019

Make abs, wrapping_abs, overflowing_abs const functions #63786

Merged

Centril added const-hack and removed needs-fcp This change is insta-stable, so needs a completed FCP to proceed. labels Sep 17, 2019

jumbatm mentioned this pull request Dec 27, 2019

Clean up const-hack PRs now that const if / match exist. #67657

Merged

jumbatm added a commit to jumbatm/rust that referenced this pull request Dec 27, 2019

Clean up const-hack from rust-lang#58044

91c2f78

RalfJung removed the const-hack label Aug 7, 2020

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Make overflowing and wrapping negation const #58044

Make overflowing and wrapping negation const #58044

Lokathor commented Feb 1, 2019

This comment has been minimized.

Lokathor commented Feb 1, 2019

This comment has been minimized.

Mark-Simulacrum commented Feb 1, 2019

oli-obk commented Feb 1, 2019

Lokathor commented Feb 2, 2019

This comment has been minimized.

oli-obk commented Feb 3, 2019

Centril commented Feb 3, 2019

kennytm commented Feb 8, 2019

rfcbot commented Feb 19, 2019

alexcrichton commented Feb 19, 2019

bors commented Feb 19, 2019

Make overflowing and wrapping negation const #58044

Make overflowing and wrapping negation const #58044

Conversation

Lokathor commented Feb 1, 2019

This comment has been minimized.

Lokathor commented Feb 1, 2019

This comment has been minimized.

Mark-Simulacrum commented Feb 1, 2019

oli-obk commented Feb 1, 2019

Lokathor commented Feb 2, 2019

This comment has been minimized.

oli-obk commented Feb 3, 2019

Centril commented Feb 3, 2019

kennytm commented Feb 8, 2019

rfcbot commented Feb 19, 2019

alexcrichton commented Feb 19, 2019

bors commented Feb 19, 2019