Add constant MAX_NEGATIVE to each floating-point value

[SciMind2460]

Since the constants fxx::MAX and fxx:MIN mirror each other, I thought it would be a good idea to add constants that fxx::MIN_POSITIVE mirrors. Hence, I have added: fxx::MAX_NEGATIVE.

#116909 is a related issue.

[rustbot]

r? @joboet

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[workingjubilee]

Please do not have commits with messages like "Update f32.rs". Describe what is actually done.

[rust-log-analyzer]

The job mingw-check-tidy failed! Check out the build log: (web) (plain)

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info: removing rustup binaries
info: rustup is uninstalled
##[group]Image checksum input
mingw-check-tidy
# We use the ghcr base image because ghcr doesn't have a rate limit
# and the mingw-check-tidy job doesn't cache docker images in CI.
FROM ghcr.io/rust-lang/ubuntu:22.04

ARG DEBIAN_FRONTEND=noninteractive
RUN apt-get update && apt-get install -y --no-install-recommends \
  g++ \
---

COPY host-x86_64/mingw-check/validate-toolstate.sh /scripts/
COPY host-x86_64/mingw-check/validate-error-codes.sh /scripts/

# NOTE: intentionally uses python2 for x.py so we can test it still works.
# validate-toolstate only runs in our CI, so it's ok for it to only support python3.
ENV SCRIPT TIDY_PRINT_DIFF=1 python2.7 ../x.py test \
           --stage 0 src/tools/tidy tidyselftest --extra-checks=py,cpp
#
# This file is autogenerated by pip-compile with Python 3.10
# by the following command:
#
#    pip-compile --allow-unsafe --generate-hashes reuse-requirements.in
---
#12 3.182 Building wheels for collected packages: reuse
#12 3.183   Building wheel for reuse (pyproject.toml): started
#12 3.394   Building wheel for reuse (pyproject.toml): finished with status 'done'
#12 3.395   Created wheel for reuse: filename=reuse-4.0.3-cp310-cp310-manylinux_2_35_x86_64.whl size=132719 sha256=d2a2565e7037ad3883fb9337653f2e25bbb588534fbef3697286cbc26d1bf634
#12 3.395   Stored in directory: /tmp/pip-ephem-wheel-cache-m2t81pcw/wheels/3d/8d/0a/e0fc6aba4494b28a967ab5eaf951c121d9c677958714e34532
#12 3.398 Successfully built reuse
#12 3.398 Installing collected packages: boolean-py, binaryornot, tomlkit, reuse, python-debian, markupsafe, license-expression, jinja2, chardet, attrs
#12 3.789 Successfully installed attrs-23.2.0 binaryornot-0.4.4 boolean-py-4.0 chardet-5.2.0 jinja2-3.1.4 license-expression-30.3.0 markupsafe-2.1.5 python-debian-0.1.49 reuse-4.0.3 tomlkit-0.13.0
#12 3.789 WARNING: Running pip as the 'root' user can result in broken permissions and conflicting behaviour with the system package manager. It is recommended to use a virtual environment instead: https://pip.pypa.io/warnings/venv
#12 4.321 Collecting virtualenv
#12 4.369   Downloading virtualenv-20.31.2-py3-none-any.whl (6.1 MB)
#12 4.499      ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 6.1/6.1 MB 47.5 MB/s eta 0:00:00
#12 4.558 Collecting platformdirs<5,>=3.9.1
#12 4.562   Downloading platformdirs-4.3.8-py3-none-any.whl (18 kB)
#12 4.600 Collecting filelock<4,>=3.12.2
#12 4.604   Downloading filelock-3.18.0-py3-none-any.whl (16 kB)
#12 4.624 Collecting distlib<1,>=0.3.7
#12 4.628   Downloading distlib-0.3.9-py2.py3-none-any.whl (468 kB)
#12 4.636      ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 469.0/469.0 KB 74.8 MB/s eta 0:00:00
#12 4.718 Installing collected packages: distlib, platformdirs, filelock, virtualenv
#12 4.908 Successfully installed distlib-0.3.9 filelock-3.18.0 platformdirs-4.3.8 virtualenv-20.31.2
#12 4.908 WARNING: Running pip as the 'root' user can result in broken permissions and conflicting behaviour with the system package manager. It is recommended to use a virtual environment instead: https://pip.pypa.io/warnings/venv
#12 DONE 5.0s

#13 [7/8] COPY host-x86_64/mingw-check/validate-toolstate.sh /scripts/
#13 DONE 0.0s
---
DirectMap4k:      145344 kB
DirectMap2M:     8243200 kB
DirectMap1G:    10485760 kB
##[endgroup]
Executing TIDY_PRINT_DIFF=1 python2.7 ../x.py test            --stage 0 src/tools/tidy tidyselftest --extra-checks=py,cpp
+ TIDY_PRINT_DIFF=1 python2.7 ../x.py test --stage 0 src/tools/tidy tidyselftest --extra-checks=py,cpp
##[group]Building bootstrap
    Finished `dev` profile [unoptimized] target(s) in 0.05s
##[endgroup]
WARN: currently no CI rustc builds have rustc debug assertions enabled. Please either set `rust.debug-assertions` to `false` if you want to use download CI rustc or set `rust.download-rustc` to `false`.
downloading https://static.rust-lang.org/dist/2025-05-12/rustfmt-nightly-x86_64-unknown-linux-gnu.tar.xz
---
##[endgroup]
[TIMING] core::build_steps::tool::ToolBuild { compiler: Compiler { stage: 0, host: x86_64-unknown-linux-gnu, forced_compiler: false }, target: x86_64-unknown-linux-gnu, tool: "tidy", path: "src/tools/tidy", mode: ToolBootstrap, source_type: InTree, extra_features: [], allow_features: "", cargo_args: [], artifact_kind: Binary } -- 37.029
[TIMING] core::build_steps::tool::Tidy { compiler: Compiler { stage: 0, host: x86_64-unknown-linux-gnu, forced_compiler: false }, target: x86_64-unknown-linux-gnu } -- 0.000
fmt check
Diff in /checkout/library/core/src/num/f64.rs:441:
     /// [`MAX_EXP`]: f64::MAX_EXP
     #[stable(feature = "assoc_int_consts", since = "1.43.0")]
     pub const MAX: f64 = 1.7976931348623157e+308_f64;
-    
+
     /// Largest negative normal `f64` value.
     ///
     /// Equal to &minus;2<sup>[`MIN_EXP`]&nbsp;&minus;&nbsp;1</sup>.
Diff in /checkout/library/core/src/num/f32.rs:443:
     #[stable(feature = "assoc_int_consts", since = "1.43.0")]
     pub const MAX: f32 = 3.40282347e+38_f32;
 
-    
     /// Largest negative normal `f32` value.
     ///
     /// Equal to &minus;2<sup>[`MIN_EXP`]&nbsp;&minus;&nbsp;1</sup>.
Diff in /checkout/library/core/src/num/f128.rs:204:
     /// [`MIN_EXP`]: f128::MIN_EXP
     #[unstable(feature = "f128", issue = "116909")]
     pub const MAX_NEGATIVE: f128 = -3.36210314311209350626267781732175260e-4932_f128;
-    
+
     /// One greater than the minimum possible *normal* power of 2 exponent
     /// for a significand bounded by 1 ≤ x < 2 (i.e. the IEEE definition).
     ///
fmt: checked 6021 files
Build completed unsuccessfully in 0:01:17
  local time: Tue May 20 14:49:12 UTC 2025
  network time: Tue, 20 May 2025 14:49:12 GMT

[joboet]

r? libs-api

[tgross35]

How could this constant be stable since 1.43 when you are adding it now? :)

New API needs an unstable gate first, and is moved to stable later.

[tgross35]

API changes need an API change proposal (ACP), which is an issue template at https://github.com/rust-lang/libs-team. You'll have to justify the use case a bit.

Personally I'm hesitant to add more repr-specific (i.e. non-mathematical) constants until we discuss something about the confusing names of the constants we do have, cc #88734.

[SciMind2460]

@tgross35 Fair enough. I thought that given that there is already MIN_POSITIVE, MAX_NEGATIVE added more symmetry between both constants.