[iAbdulrrahman]

What

Implement FreeBSD/POSIX bit search operations ffs, ffsl, ffsll, fls, and flsll in libc using C++20 std::countr_zero and std::countl_zero.

Tested

Windows 11 x86_64, unit tests in GuestWideStrings.cpp exercising zero, power-of-two, signed boundaries (INT_MIN, INT64_MIN, LLONG_MIN), arbitrary bit patterns, and all-ones (-1) for each routine.

Checklist

• Based on current main; no other open PR implements the same functions
• One topic per PR; follow-ups go in a new PR
• No comments in code except technical debt
• Unimplemented paths throw (NotImplemented_nid_no_patch); silent stubs are listed under Silent stubs in their library's technical debt file
• No notes, investigation .md files or images added to the repository (attach them to this PR)
• New third-party code is a submodule built from source
• Generic behaviour, not specific to one title
• Depends on: none
• Fixes: none
• Unblocks: none
• GPUs tested: n/a
• AI-assisted: yes

[github-actions]

Progress report (88795ed → 91d5a05)

📈 System libraries: 51.12% (+0.02%, +5 implemented functions)

✅ 5 implemented

Library	Name
libc	ffs_nid_postfix
libc	ffsl_nid_postfix
libc	ffsll_nid_postfix
libc	fls_nid_postfix
libc	flsll_nid_postfix

Changed libraries (implemented exports)

Library	Before	After	Change
libc	1373/1384 (99.21%)	1378/1389 (99.21%)	+0.00 pp

[MarcZX10]

I reviewed the exact head . The bit-index arithmetic is consistent with the BSD / convention: zero returns 0, otherwise indices are one-based; converting signed inputs to the corresponding unsigned width preserves the sign-bit cases. The added cases cover zero, low/high bits, all-ones and signed minima. The conventions check and pass on this head. I could not run locally: the available configured build is relinker-only, and the hosted Linux/Windows product jobs are skipped by path policy. The relinker/ASan matrix is still completing, so those jobs are not evidence for the libc test.\n\nThe branch is based on , while current is . CONTRIBUTING.md asks branches to stay up to date with . The intervening main changes do not touch these three files, and I found no implementation defect in this review, but please sync the branch and rerun the focused test before approval.

[MarcZX10]

Correction to my review body above: its inline-code formatting was stripped by the shell, so the displayed text omitted identifiers. The intended findings are: I reviewed head 5b1905f; the ffs/fls bit-index arithmetic is consistent with BSD convention (zero -> 0, otherwise one-based), and the unsigned conversions cover signed-minimum cases. Conventions and git diff --check pass. I could not run guest_wide_strings locally because the available build is relinker-only; hosted Linux/Windows product jobs are skipped by path policy.

Current main is 88795ed, while this branch is based on 48c160c. CONTRIBUTING.md requires branches to stay current. The intervening main changes do not touch these three files. Please sync and run guest_wide_strings; I found no code defect, but the sync/test condition remains before approval.

[iAbdulrrahman]

Synced to current upstream main (88795ed), re-verified conventions check, and confirmed tests pass on the updated head.

[MarcZX10]

Thanks for syncing. I fetched exact head 91d5a05; its merge-base is current main 88795ed. I compiled the changed Strings.cpp with the PR header and ran a focused harness comparing all five functions against independent std::bit expectations for 100,000 generated 32/64-bit patterns plus INT_MIN, INT64_MIN and LLONG_MIN. The harness passed. Current-main conventions and git diff --check pass; the published Windows test report is consistent with this result. The hosted relinker jobs are still running and product Linux/Windows jobs are skipped by path policy; those checks do not exercise the libc changes. No defect found; approved.

[MarcZX10]

Thanks for syncing. I fetched exact head 91d5a05; its merge-base is current main 88795ed. I compiled the changed Strings.cpp with the PR header and ran a focused harness comparing all five functions against independent std::bit expectations for 100,000 generated 32/64-bit patterns plus INT_MIN, INT64_MIN and LLONG_MIN. The harness passed. Current-main conventions and git diff --check pass; the published Windows test report is consistent with this result. Hosted product Linux/Windows tests are skipped by path policy. No implementation defect found; approved.

[github-actions]

Some comparisons could not be completed because a pull request conflicts with the base branch. Review these shared files manually before concluding that there is no overlap.

Pull request	Shared files not compared
PR 5021	core/libs/prx/libc/src/Strings.cpp
PR 7851	core/libs/prx/libc/include/Api.hpp
PR 10324	core/libs/prx/libc/include/Api.hpp
PR 10749	core/libs/prx/libc/include/Api.hpp
PR 11341	core/libs/prx/libc/src/Strings.cpp

[MarcZX10]

I manually checked the incomplete overlap warnings against the PR-file patches: #11341 changes only the wcstold platform assertions; #5021 changes the integer parsers/QuietNan and does not touch the bit-search additions; #7201 changes the integer-parser wrapper paths; #7851 changes only _Atomic_assert’s declaration; and #9772 adds _Stopfx declarations. None changes the new ffs/fls functions or their assertions, so I see no merge dependency for this patch.