common/snprintf.c: preserve wide integer values

[user01010111]

Summary

• Carry integer magnitudes as unsigned LLONG through the fallback formatter, with signedness tracked separately.
• Retrieve %o, %u, %x and %X arguments directly into unsigned storage instead of passing them through a possibly narrower signed long.
• Convert %p through size_t before widening, avoiding pointer sign extension on conventional 32-bit and LLP64 targets.
• Retain unsigned negation for negative signed values so LLONG_MIN is handled without signed overflow.
• Extend TEST_SNPRINTF with focused UINT_MAX, ULONG_MAX, ULLONG_MAX, top-bit hexadecimal and full-width octal comparisons.

Fixes #1602

Review follow-up

Wider ABI testing prompted by review found that the previous PR head regressed the narrow unsigned conversions on systems where long is narrower than long long. On native Windows LLP64, %u with UINT_MAX was widened through negative long and printed as 18446744073709551615; the %o, %x, %X and corresponding unsigned long cases failed in the same way.

Casting later inside fmtint() cannot repair a value already changed by the earlier signed conversion. This revision instead keeps unsigned values unsigned from va_arg() through digit conversion. For signed decimal formats, the caller supplies the converted unsigned value and its sign separately; fmtint() negates only the unsigned value when producing the magnitude. Plain -value is not used because it overflows for LLONG_MIN.

Validation

• Native Windows 11 x64, MSYS2 MinGW64 GCC 16.2.0 Rev3, LLP64:
  • exact PR head failed 8 of 13 focused integer/pointer comparisons;
  • the revised source passed all 13;
  • the expanded built-in comparison passed 196/196;
  • a native forced-fallback configure confirmed snprintf and vsnprintf unavailable and HAVE_LONG_LONG_INT=1;
  • make -C common V=1 snprintf.lo passed with GNU99, -pedantic and -Werror, producing a PE x86-64 object.
• Native Linux ILP32 GCC:
  • exact PR head failed nine focused cases and emitted -Wpointer-to-int-cast;
  • the revised source passed 13/13 and the built-in comparison passed 196/196.
• Native Linux LP64:
  • focused and built-in comparisons passed with GCC 16.2.1 and Clang 22.1.8;
  • GNU89 and strict C99/pedantic builds passed with warnings as errors;
  • Clang UBSan passed, including LLONG_MIN.
• Forced-fallback project object builds passed with GCC and Clang.
• make stylecheck, the non-ASCII source check and git diff --check passed.
• -Wconversion -Wsign-conversion still reports 11 pre-existing diagnostics in this legacy file; this revision removes the additional signed-to-unsigned diagnostic introduced by the previous PR head and adds none.

No upstream CI result is claimed for this revision until it is published.

General C checklist

• Integer widths and signedness are carried explicitly without assuming long matches pointers or long long.
• The change follows the existing fallback implementation and in-file test placement; no new helper, dependency or file is introduced.
• Coding style and whitespace follow common/snprintf.c and docs/developers.txt precedent.
• No build, distribution or documentation list needs updating.

AI assistance

OpenAI Codex gpt-5.6-sol with xhigh reasoning was used for repository analysis, implementation, review, drafting and local/native validation. Anthropic Claude Fable 5 (claude-fable-5) with xhigh reasoning performed an independent adversarial review and produced a prototype used as design evidence. The human contributor reviewed the complete diff and validation evidence and remains responsible for the contribution.

[github-actions]

A ZIP file with standard source tarball and another tarball with pre-built docs for commit 9d8e1f6 is temporarily available: NUT-tarballs-PR-3598.zip.

[user01010111]

The CentOS 8/ppc64le OBS failure occurs during RPM database initialisation, before %prep or any source compilation:

BDB0091 DB_VERSION_MISMATCH: Database environment version mismatch

CentOS 9/ppc64le builds this commit successfully. Could the CentOS 8/ppc64le preinstall image (a0769ebbc600e42fa9742d61cacaedd7) be refreshed before rerunning the target?

[AppVeyorBot]

✅ Build nut 2.8.5.5161-master completed (commit ee81f6e695 by @)

• artifacts
• A 7-zip archive with built NUT for Windows debug binaries is temporarily available: NUT-for-Windows-x86_64-SNAPSHOT-2.8.5.5161-master.7z

[AppVeyorBot]

✅ Build nut 2.8.5.5161-master completed (commit ee81f6e695 by @)

[jimklimov]

OBS scenarios are on Open Build System, following their dependency tree etc. - as often as they regenerate them. I gather there is a regular inability to start the (emulated?) builders for this platform, which is mostly worked around by persistent restarting of the build in their Web-UI...

[jimklimov]

I think the signed number support got broken here, the rest seems OK, thanks.

[AppVeyorBot]

❌ Build nut 2.8.5.5192-master failed (commit b9e44ad8bc by @)

• artifacts (if any)

[AppVeyorBot]

❌ Build nut 2.8.5.5193-master failed (commit 0e490faa08 by @)

• artifacts (if any)