f*::NAN: guarantee that this is a quiet NaN #139483

RalfJung · 2025-04-07T13:23:55Z

I think we should guarantee that this is a quiet NaN. This then implies that programs not using f*::from_bits (or unsafe type conversions) are guaranteed to only work with quiet NaNs. It would be awkward if people start to write 0.0 / 0.0 instead of using the constant just because they want to get a guaranteed-quiet NaN.

This is a @rust-lang/libs-api change. The definition of this constant currently is 0.0 / 0.0, which is already guaranteed to be a quiet NaN. So all this does is forward that guarantee to our users.

rustbot · 2025-04-07T13:24:01Z

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m-ou-se · 2025-04-07T14:39:49Z

@rfcbot merge

rfcbot · 2025-04-07T14:39:52Z

Team member @m-ou-se has proposed to merge this. The next step is review by the rest of the tagged team members:

No concerns currently listed.

Once a majority of reviewers approve (and at most 2 approvals are outstanding), this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up!

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library/core/src/num/f128.rs

rustbot · 2025-04-07T15:00:37Z

The Miri subtree was changed

cc @rust-lang/miri

rfcbot · 2025-04-07T17:06:19Z

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

bstrie · 2025-04-10T11:50:39Z

Is it worth considering the alternative of making no guarantees about f*::NAN, and instead providing f*::QUIET_NAN and f*::SIGNALING_NAN?

RalfJung · 2025-04-10T11:58:55Z

I think adding a SIGNALING_NAN might be worth considering, but I'd say NAN is the better name for QUIET_NAN since it's what you should use most of the time. Signaling NaNs show non-portable behavior much more quickly than quiet NaNs.

rfcbot · 2025-04-17T17:07:37Z

The final comment period, with a disposition to merge, as per the review above, is now complete.

As the automated representative of the governance process, I would like to thank the author for their work and everyone else who contributed.

This will be merged soon.

tgross35 · 2025-04-17T18:26:25Z

r? tgross35
@bors r+ rollup

bors · 2025-04-17T18:26:28Z

📌 Commit 0da46d1 has been approved by tgross35

It is now in the queue for this repository.

…iaskrgr Rollup of 8 pull requests Successful merges: - rust-lang#139351 (Autodiff batching2) - rust-lang#139483 (f*::NAN: guarantee that this is a quiet NaN) - rust-lang#139498 (Ignore zero-sized types in wasm future-compat warning) - rust-lang#139967 (Introduce and use specialized `//@ ignore-auxiliary` for test support files instead of using `//@ ignore-test`) - rust-lang#139969 (update libc) - rust-lang#139971 (Make C string merging test work on MIPS) - rust-lang#139974 (Change `InterpCx::instantiate*` function visibility to pub) - rust-lang#139977 (Fix drop handling in `hint::select_unpredictable`) r? `@ghost` `@rustbot` modify labels: rollup

Rollup merge of rust-lang#139483 - RalfJung:nan, r=tgross35 f*::NAN: guarantee that this is a quiet NaN I think we should guarantee that this is a quiet NaN. This then implies that programs not using `f*::from_bits` (or unsafe type conversions) are guaranteed to only work with quiet NaNs. It would be awkward if people start to write `0.0 / 0.0` instead of using the constant just because they want to get a guaranteed-quiet NaN. This is a `@rust-lang/libs-api` change. The definition of this constant currently is `0.0 / 0.0`, which is already guaranteed to be a quiet NaN. So all this does is forward that guarantee to our users.

tgross35 · 2025-04-18T00:59:38Z

I didn't think of this until just now but we should add a test ensuring the top mantissa bit is set

f*::NAN: guarantee that this is a quiet NaN I think we should guarantee that this is a quiet NaN. This then implies that programs not using `f*::from_bits` (or unsafe type conversions) are guaranteed to only work with quiet NaNs. It would be awkward if people start to write `0.0 / 0.0` instead of using the constant just because they want to get a guaranteed-quiet NaN. This is a `@rust-lang/libs-api` change. The definition of this constant currently is `0.0 / 0.0`, which is already guaranteed to be a quiet NaN. So all this does is forward that guarantee to our users.

RalfJung · 2025-04-20T09:21:00Z

@tgross35 what's the best way to get the top mantissa bit for our various float types?

tgross35 · 2025-04-20T21:38:17Z

I think x.to_bits() & (1 << (F::MANTISSA_DIGITS - 2)) != 0 should work

test_nan: ensure the NAN contant is quiet Follow-up to rust-lang#139483 r? `@tgross35`

test_nan: ensure the NAN contant is quiet Follow-up to rust-lang#139483 r? ``@tgross35``

Rollup merge of rust-lang#140149 - RalfJung:test_nan, r=tgross35 test_nan: ensure the NAN contant is quiet Follow-up to rust-lang#139483 r? ``@tgross35``

test_nan: ensure the NAN contant is quiet Follow-up to rust-lang/rust#139483 r? ``@tgross35``

test_nan: ensure the NAN contant is quiet Follow-up to rust-lang#139483 r? ``@tgross35``

Pkgsrc changes: * Adjust patches to adapt to upstream changes and new versions. * associated checksums Upstream changes relative to 1.87.0: Version 1.88.0 (2025-06-26) ========================== Language -------- - [Stabilize `#![feature(let_chains)]` in the 2024 edition.] (rust-lang/rust#132833) This feature allows `&&`-chaining `let` statements inside `if` and `while`, allowing intermixture with boolean expressions. The patterns inside the `let` sub-expressions can be irrefutable or refutable. - [Stabilize `#![feature(naked_functions)]`.] (rust-lang/rust#134213) Naked functions allow writing functions with no compiler-generated epilogue and prologue, allowing full control over the generated assembly for a particular function. - [Stabilize `#![feature(cfg_boolean_literals)]`.] (rust-lang/rust#138632) This allows using boolean literals as `cfg` predicates, e.g. `#[cfg(true)]` and `#[cfg(false)]`. - [Fully de-stabilize the `#[bench]` attribute] (rust-lang/rust#134273). Usage of `#[bench]` without `#![feature(custom_test_frameworks)]` already triggered a deny-by-default future-incompatibility lint since Rust 1.77, but will now become a hard error. - [Add warn-by-default `dangerous_implicit_autorefs` lint against implicit autoref of raw pointer dereference.] (rust-lang/rust#123239) The lint [will be bumped to deny-by-default] (rust-lang/rust#141661) in the next version of Rust. - [Add `invalid_null_arguments` lint to prevent invalid usage of null pointers.] (rust-lang/rust#119220) This lint is uplifted from `clippy::invalid_null_ptr_usage`. - [Change trait impl candidate preference for builtin impls and trivial where-clauses.] (rust-lang/rust#138176) - [Check types of generic const parameter defaults] (rust-lang/rust#139646) Compiler -------- - [Stabilize `-Cdwarf-version` for selecting the version of DWARF debug information to generate.] (rust-lang/rust#136926) Platform Support ---------------- - [Demote `i686-pc-windows-gnu` to Tier 2.] (https://blog.rust-lang.org/2025/05/26/demoting-i686-pc-windows-gnu/) Refer to Rust's [platform support page][platform-support-doc] for more information on Rust's tiered platform support. [platform-support-doc]: https://doc.rust-lang.org/rustc/platform-support.html Libraries --------- - [Remove backticks from `#[should_panic]` test failure message.] (rust-lang/rust#136160) - [Guarantee that `[T; N]::from_fn` is generated in order of increasing indices.] (rust-lang/rust#139099), for those passing it a stateful closure. - [The libtest flag `--nocapture` is deprecated in favor of the more consistent `--no-capture` flag.] (rust-lang/rust#139224) - [Guarantee that `{float}::NAN` is a quiet NaN.] (rust-lang/rust#139483) Stabilized APIs --------------- - [`Cell::update`] (https://doc.rust-lang.org/stable/std/cell/struct.Cell.html#method.update) - [`impl Default for *const T`] (https://doc.rust-lang.org/nightly/std/primitive.pointer.html#impl-Default-for-*const+T) - [`impl Default for *mut T`] (https://doc.rust-lang.org/nightly/std/primitive.pointer.html#impl-Default-for-*mut+T) - [`HashMap::extract_if`] (https://doc.rust-lang.org/stable/std/collections/struct.HashMap.html#method.extract_if) - [`HashSet::extract_if`] (https://doc.rust-lang.org/stable/std/collections/struct.HashSet.html#method.extract_if) - [`proc_macro::Span::line`] (https://doc.rust-lang.org/stable/proc_macro/struct.Span.html#method.line) - [`proc_macro::Span::column`] (https://doc.rust-lang.org/stable/proc_macro/struct.Span.html#method.column) - [`proc_macro::Span::start`] (https://doc.rust-lang.org/stable/proc_macro/struct.Span.html#method.start) - [`proc_macro::Span::end`] (https://doc.rust-lang.org/stable/proc_macro/struct.Span.html#method.end) - [`proc_macro::Span::file`] (https://doc.rust-lang.org/stable/proc_macro/struct.Span.html#method.file) - [`proc_macro::Span::local_file`] (https://doc.rust-lang.org/stable/proc_macro/struct.Span.html#method.local_file) These previously stable APIs are now stable in const contexts: - [`NonNull<T>::replace`] (https://doc.rust-lang.org/stable/std/ptr/struct.NonNull.html#method.replace) - [`<*mut T>::replace`] (https://doc.rust-lang.org/stable/std/primitive.pointer.html#method.replace) - [`std::ptr::swap_nonoverlapping`] (rust-lang/rust#137280) - [`Cell::{replace, get, get_mut, from_mut, as_slice_of_cells}`] (rust-lang/rust#137928) Cargo ----- - [Stabilize automatic garbage collection.] (rust-lang/cargo#14287) - [use `zlib-rs` for gzip compression in rust code] (rust-lang/cargo#15417) Rustdoc ----- - [Doctests can be ignored based on target names using `ignore-*` attributes.] (rust-lang/rust#137096) - [Stabilize the `--test-runtool` and `--test-runtool-arg` CLI options to specify a program (like qemu) and its arguments to run a doctest.] (rust-lang/rust#137096) Compatibility Notes ------------------- - [Finish changing the internal representation of pasted tokens] (rust-lang/rust#124141). Certain invalid declarative macros that were previously accepted in obscure circumstances are now correctly rejected by the compiler. Use of a `tt` fragment specifier can often fix these macros. - [Fully de-stabilize the `#[bench]` attribute] (rust-lang/rust#134273). Usage of `#[bench]` without `#![feature(custom_test_frameworks)]` already triggered a deny-by-default future-incompatibility lint since Rust 1.77, but will now become a hard error. - [Fix borrow checking some always-true patterns.] (rust-lang/rust#139042) The borrow checker was overly permissive in some cases, allowing programs that shouldn't have compiled. - [Update the minimum external LLVM to 19.] (rust-lang/rust#139275) - [Make it a hard error to use a vector type with a non-Rust ABI without enabling the required target feature.] (rust-lang/rust#139309)

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rfcbot added proposed-final-comment-period Proposed to merge/close by relevant subteam, see T-<team> label. Will enter FCP once signed off. disposition-merge This issue / PR is in PFCP or FCP with a disposition to merge it. labels Apr 7, 2025

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library/core/src/num/f128.rs Outdated Show resolved Hide resolved

RalfJung added 2 commits April 7, 2025 17:00

f*::NAN: guarantee that this is a quiet NaN

da0b9a2

targest → targets (spotted as I had the same typo)

0da46d1

RalfJung force-pushed the nan branch from 9de9aff to 0da46d1 Compare April 7, 2025 15:00

rfcbot added final-comment-period In the final comment period and will be merged soon unless new substantive objections are raised. and removed proposed-final-comment-period Proposed to merge/close by relevant subteam, see T-<team> label. Will enter FCP once signed off. labels Apr 7, 2025

m-ou-se mentioned this pull request Apr 7, 2025

Different NaN behavior with various float functions on beta-vs-stable #139487

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RalfJung mentioned this pull request Apr 7, 2025

Enable Non-determinism of float operations in Miri and change std tests #138062

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rustbot mentioned this pull request Apr 17, 2025

Tracking issue for release notes of #139483: f*::NAN: guarantee that this is a quiet NaN #139986

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bors added the S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. label Apr 17, 2025

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Rollup of 8 pull requests #139992

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bors merged commit b6e48d3 into rust-lang:master Apr 18, 2025
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RalfJung deleted the nan branch April 20, 2025 09:12

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test_nan: ensure the NAN contant is quiet #140149

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Rollup merge of rust-lang#140149 - RalfJung:test_nan, r=tgross35

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test_nan: ensure the NAN contant is quiet Follow-up to rust-lang#139483 r? `@tgross35`

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Rollup merge of rust-lang#140149 - RalfJung:test_nan, r=tgross35

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test_nan: ensure the NAN contant is quiet Follow-up to rust-lang#139483 r? ``@tgross35``

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Unrolled build for rust-lang#140149

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Rollup merge of rust-lang#140149 - RalfJung:test_nan, r=tgross35 test_nan: ensure the NAN contant is quiet Follow-up to rust-lang#139483 r? ``@tgross35``

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Rollup merge of #140149 - RalfJung:test_nan, r=tgross35

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