libc: Add C23 stdbit.h with optional Kconfig and generic implementation by arjav1528 · Pull Request #18347 · apache/nuttx

arjav1528 · 2026-02-03T17:21:37Z

Fixes: #18311

Summary

Add optional C23 stdbit.h support so builds can provide <stdbit.h> when the toolchain does not. Follows the same pattern as stdarg.h / math.h: redirect at include/nuttx/lib/stdbit.h, copied to include/stdbit.h when enabled.

Kconfig: ARCH_HAVE_STDBIT_H, ARCH_STDBIT_H (arch-specific), LIBC_STDBIT_GENERIC (generic on any arch).
Header: Generic implementation using __builtin_clz/__builtin_ctz/__builtin_popcount for all C23 stdbit macros; archs may provide arch/<arch>/include/stdbit.h.
Build: Unix.mk, Win.mk, CMake copy the header when either option is set.
Libc: Optional libs/libc/stdbit/stdbit_verify.c (compile-time check when stdbit enabled).
Docs: Documentation/legacy_README.md and Documentation/components/libs/libc/index.rst.

Impact

Users: Optional; no change unless ARCH_STDBIT_H or LIBC_STDBIT_GENERIC is enabled. Code can then use C23 <stdbit.h> macros when the toolchain lacks them.
Build: One header is copied to include/stdbit.h when stdbit support is enabled; build system (Unix.mk, Win.mk, CMake) is extended only for this copy.
Compatibility: Improves portability for C23 stdbit usage on toolchains that don’t yet ship stdbit.h. No impact on existing configs that don’t enable it.

Testing

There is no freely available, upstream test suite for C23 stdbit.h that we could add to NuttX to validate this implementation. Verification is limited to:

Enabling LIBC_STDBIT_GENERIC (or arch-specific ARCH_STDBIT_H where implemented) and confirming the build completes and stdbit_verify.c compiles (compile-time checks that the macros expand as expected).
Manual inspection that the generic implementation matches C23 semantics and uses the intended builtins.

michallenc

That was fast, nice work! Please squash the commits ideally into two - one implementing stdbit and other updating the documentation. Also fix long lines in stdbit.h causing CI to fail.

We definitely need proper tests before merging this. These should go to app repository. I can write some, but won't get to it until next week probably.

include/nuttx/lib/stdbit.h

Kconfig

tools/Unix.mk

michallenc · 2026-02-04T21:33:31Z

Seems the merge request now contains completely different commits unrelated to the title and previous changes.

linguini1

Please check that your PR follows the contributing guidelines. Also, a mistake might have happened during rebase/squashing that has caused your commits to disappear, as Michal pointed out.

arjav1528 · 2026-02-09T12:44:44Z

@michallenc @linguini1 could you please help me with the failing test cases

Sure, the commit message is missing. It should be in format
title - short info what is changed

description - more detailed text describing what you did and why

sign-off
You only have title and sign of in your commits.
understood, and about the other test failing?
right, sorry, I missed that one. Seems like esp only problem when downloading MCUboot and not caused by this MR I think, @tmedicci could you take a look please?
is it possible that the testcase might have stopped bcoz of a timeout error or something similar??, coz in the logs I cant see anything wrong, it is getting built, then cleaned up, and repeat
Yes, it may happen. You can try force pushing the branch to restart the CI.

done, could you please review the PR and approve the workflow

include/nuttx/lib/stdbit.h

arjav1528 · 2026-02-14T15:12:00Z

@michallenc could you please approve the workflows again :(

arjav1528 · 2026-02-18T18:39:59Z

@michallenc could you please approve the workflows again as I have force pushed new commits

arjav1528 · 2026-02-23T15:30:05Z

@michallenc is this same timeout issue, or is anything wrong??

michallenc · 2026-02-23T16:18:52Z

Not sure here honestly. @simbit18 @acassis do you have some ideas what's wrong with CI here?

simbit18 · 2026-02-23T16:34:59Z

@michallenc restarted the workflow

arjav1528 · 2026-02-23T18:00:20Z

@michallenc restarted the workflow

same issue, ig it might be due to multiple PR workflows in the repo, so the CPU load increases which results in the slower builds and hence timeouts

simbit18 · 2026-02-23T18:01:02Z

@arjav1528 please rebase
you need to update your branch

CONFIG_INTERPRETER_LUA_32BIT has been renamed with this PR #18398
CONFIG_INTERPRETER_LUA_32BIT -> CONFIG_INTERPRETERS_LUA_32BIT

====================================================================================
Configuration/Tool: sim/lua
2026-02-23 17:09:58
------------------------------------------------------------------------------------
  Cleaning...
  Configuring...
  Building NuttX...
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  0     0    0      %  0T o t a l0        %  0R e c e i v e0d   %   X f e0r d- - :A-v-e:r-a-g e- -S:p-e-e:d- -   T-i-m:e- - : - -T im e      0  Time  Current
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  [1/1] Normalize sim/lua
8d7
< # CONFIG_INTERPRETER_LUA_32BIT is not set
Saving the new configuration file
HEAD detached at pull/18347/merge
Changes not staged for commit:
  (use "git add <file>..." to update what will be committed)
  (use "git restore <file>..." to discard changes in working directory)
	modified:   boards/sim/sim/sim/configs/lua/defconfig

no changes added to commit (use "git add" and/or "git commit -a")
====================================================================================

arjav1528 · 2026-02-23T18:07:19Z

@simbit18 done, could you approve the workflows..

xiaoxiang781216 · 2026-02-24T03:18:55Z

include/nuttx/lib/stdbit.h

+ * C23 endianness macros (reuse LITTLE_ENDIAN/BIG_ENDIAN from sys/endian.h)
+ ****************************************************************************/
+
+#  include <sys/endian.h>


move after line 37

not fix yet

include/nuttx/lib/stdbit.h

xiaoxiang781216 · 2026-02-24T03:31:30Z

include/nuttx/lib/stdbit.h

+ *
+ ****************************************************************************/
+
+#ifndef __INCLUDE_NUTTX_LIB_STDBIT_H


squash your change into one patch

arjav1528 · 2026-02-24T19:30:14Z

done @xiaoxiang781216, could you please approve the workflows

xiaoxiang781216 · 2026-02-25T02:46:13Z

done @xiaoxiang781216, could you please approve the workflows

please fix the ci issue before asking review:
https://github.com/apache/nuttx/actions/runs/22354112984/job/64759945293?pr=18347

Error: /home/runner/work/nuttx/nuttx/nuttx/include/nuttx/lib/stdbit.h:85:78: error: Long line found
Error: /home/runner/work/nuttx/nuttx/nuttx/include/nuttx/lib/stdbit.h:90:80: error: Long line found
Error: /home/runner/work/nuttx/nuttx/nuttx/include/nuttx/lib/stdbit.h:113:78: error: Long line found
Error: /home/runner/work/nuttx/nuttx/nuttx/include/nuttx/lib/stdbit.h:118:80: error: Long line found
Error: /home/runner/work/nuttx/nuttx/nuttx/include/nuttx/lib/stdbit.h:149:45: error: Upper case hex constant found
Error: /home/runner/work/nuttx/nuttx/nuttx/include/nuttx/lib/stdbit.h:149:84: error: Long line found
Error: /home/runner/work/nuttx/nuttx/nuttx/include/nuttx/lib/stdbit.h:154:46: error: Upper case hex constant found
Error: /home/runner/work/nuttx/nuttx/nuttx/include/nuttx/lib/stdbit.h:204:45: error: Upper case hex constant found
Error: /home/runner/work/nuttx/nuttx/nuttx/include/nuttx/lib/stdbit.h:210:46: error: Upper case hex constant found

- Introduced Kconfig options for stdbit.h, allowing architecture-specific and generic implementations. - Added new documentation for stdbit.h, detailing its usage and configuration. - Updated CMake and Makefile to handle the inclusion of stdbit.h based on configuration settings. This enhances the NuttX library with optional C23 bit manipulation utilities, improving functionality for architectures that support it. Signed-off-by: Arjav Patel <arjav1528@gmail.com>

arjav1528 requested review from Donny9, anchao, fdcavalcanti, jerpelea, raiden00pl, simbit18, xiaoxiang781216 and yf13 as code owners February 3, 2026 17:21

github-actions bot added Area: Documentation Improvements or additions to documentation Area: Tooling Area: Build system Area: OS Components OS Components issues Size: M The size of the change in this PR is medium labels Feb 3, 2026

linguini1 requested a review from michallenc February 3, 2026 17:47

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arjav1528 force-pushed the dev-issue-18311 branch 2 times, most recently from ad2e28a to 277c277 Compare February 4, 2026 12:43

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arjav1528 force-pushed the dev-issue-18311 branch 2 times, most recently from 8abb829 to 8e473c0 Compare February 4, 2026 16:46

arjav1528 requested review from GUIDINGLI and yamt as code owners February 4, 2026 16:46

github-actions bot added Arch: arm64 Issues related to ARM64 (64-bit) architecture Size: XS The size of the change in this PR is very small and removed Area: Documentation Improvements or additions to documentation Area: Tooling Area: Build system labels Feb 4, 2026

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arjav1528 dismissed linguini1’s stale review via a9148f2 February 12, 2026 10:38

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arjav1528 force-pushed the dev-issue-18311 branch from a9148f2 to ada86ea Compare February 16, 2026 17:51

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github-actions bot removed Area: Documentation Improvements or additions to documentation Area: Tooling Size: XS The size of the change in this PR is very small labels Feb 23, 2026

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arjav1528 requested a review from xiaoxiang781216 February 25, 2026 06:14

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arjav1528 commented Feb 3, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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Fixes: #18311

Summary

Impact

Testing

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