arnavsharma990 opened a new issue, #21213:
URL: https://github.com/apache/nuttx/issues/21213
### Description / Steps to reproduce the issue
<html><head></head><body><h3><span>What is the
bug?</span></h3><p><code><span>include/nuttx/lib/math32.h</span></code><span>
guards the optimized constant 64-bit division path
(</span><code><span>div64_const</span></code><span> /
</span><code><span>div64_const32</span></code><span>) behind
</span><code><span>CONFIG_HAVE_EXPRESSION_STATEMENT</span></code><span>. This
symbol is never defined anywhere in the repository, making the guard
permanently false. Consequently, affected call sites fall back to ordinary
64-bit division, potentially pulling in software division helpers
(</span><code><span>__aeabi_ldivmod</span></code><span> /
</span><code><span>_udivmoddi4</span></code><span>) on 32-bit
targets.</span></p><h3><span>Why is this a bug?</span></h3><p><span>The
optimization was introduced in commit
</span><code><span>7fc03e0084</span></code><span> but guarded by two undefined
symbols: </span><code><span>CONFIG_HAVE_LONG_LONG</span></code><span> and
</span><code><span>CONFIG_HAVE_EX
PRESSION_STATEMENT</span></code><span>. Commit
</span><code><span>c32b683</span></code><span> later removed the first guard,
leaving the optimization dependent on
</span><code><span>CONFIG_HAVE_EXPRESSION_STATEMENT</span></code><span>, which
is still undefined.</span></p><h3><span>Steps to reproduce</span></h3><ol
start="1"><li><p><span>Run:</span></p><pre><code><span>grep -rn
"HAVE_EXPRESSION_STATEMENT" nuttx nuttx-apps</span></code></pre><p><span>Only
match:
</span><code><span>include/nuttx/lib/math32.h:321</span></code><span>.</span></p></li><li><p><span>Confirm
no Kconfig definition exists:</span></p><pre><code><span>grep -rn "config
HAVE_EXPRESSION_STATEMENT" nuttx</span></code></pre></li><li><p><span>Inspect
</span><code><span>math32.h</span></code><span>:</span></p><ul><li><p><span>Lines
262–318:
</span><code><span>div64_const32</span></code><span>.</span></p></li><li><p><span>Lines
321–346: guarded
</span><code><span>div64_const</span></code><span>.</span></p></li><li><p
><span>Lines 348–352: fallback division
>wrappers.</span></p></li></ul></li><li><p><span>Build a minimal 32-bit target
>with a non-power-of-two tick rate and inspect the linker map. The clock path
>uses </span><code><span>__aeabi_ldivmod</span></code><span> instead of the
>intended reciprocal multiplication.</span></p></li></ol><h3><span>Affected
>call
>sites</span></h3><ul><li><p><code><span>include/nuttx/clock.h</span></code><span>
> — clock conversion functions and
>macros.</span></p></li><li><p><code><span>sched/wdog/wd_start.c:369</span></code><span>
> — watchdog
>timing.</span></p></li><li><p><code><span>include/nuttx/timers/oneshot.h:366</span></code><span>
> — oneshot
>timer.</span></p></li><li><p><code><span>include/nuttx/timers/clkcnt.h</span></code><span>
> — clock counter conversions.</span></p></li></ul><h3><span>Measured
>improvement</span></h3><p><span>Controlled experiment on
></span><code><span>stm32f4discovery</span></code><span> minimal
>build:</span></p>
| Text | Data | BSS
-- | -- | -- | --
Baseline | 28,212 | 800 | 2,136
Optimized guard enabled | 28,108 | 800 | 2,136
Difference | −104 | 0 | 0
<p><span>Disassembly confirmed that
</span><code><span>clock_systime_timespec</span></code><span> replaced the
</span><code><span>__aeabi_ldivmod</span></code><span> call with hardware
multiply instructions (</span><code><span>umlal</span></code><span>). This
measurement is specific to this configuration.</span></p><h3><span>Compiler
portability</span></h3><p><span>The optimized macros use GNU statement
expressions and </span><code><span>typeof</span></code><span>. GCC and Clang
support these, but Green Hills (</span><code><span>__ghs__</span></code><span>)
compatibility needs consideration. The replacement guard should follow NuttX's
existing compiler capability conventions. I am leaving the exact portable
solution open for maintainer discussion.</span></p></body></html>
### On which OS does this issue occur?
[OS: Mac]
### What is the version of your OS?
macOS (Darwin)
### NuttX Version
master (commit `635ac55e50`)
### Issue Architecture
[Arch: arm]
### Issue Area
[Area: Other], [Area: Build System]
### Host information
`arm-none-eabi-gcc 16.2.0` (Homebrew), `make` host_info not available for
this configuration
### Verification
- [x] I have verified before submitting the report.
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