Brijesh-Thakkar opened a new pull request, #21212:
URL: https://github.com/apache/nuttx/pull/21212
## Summary
`clock_basetime()` computes the initial time as `tv_sec = jdn *
SEC_PER_DAY`, where `jdn` is
promoted to 64-bit. On targets without a native 64-bit multiply this pulls
in libgcc's
`__muldi3`.
`jdn` is the day count from `clock_calendar2utc()` for `CONFIG_START_YEAR`
(>= 1970), so it is
non-negative and well below 2^32 (at most ~49,710 for the allowed year
range). A 32x32->64
multiply is therefore sufficient:
tp->tv_sec = (uint64_t)(uint32_t)jdn * SEC_PER_DAY;
A comment in the code documents why the cast is safe.
This is a small follow-up from the size investigation in #18849: after
#20996, this is the
only remaining 64-bit libgcc call site in the common clock code where a
portable C change
reduces size on AVR. Replacing the remaining 64-bit divisions with portable
C was measured to
be larger than libgcc's routines on AVR, so it is not proposed.
Refs #18849
## Impact
- No functional change; same result for every legal `jdn` (verified, see
Testing).
- No API/ABI change; `time_t` stays `int64_t`.
- Size (master 3122150b1f vs this PR, `size` total in bytes):
| config | master | this PR | delta | notes |
|---|---:|---:|---:|---|
| breadxavr:nsh (AVR, avr-gcc 14.3.0) | 58485 | 58403 | **-82** | `__muldi3`
replaced by smaller `__umulsidi3` |
| stm32vldiscovery:nsh (Cortex-M3) | 40680 | 40684 | +4 | text identical; +4
is `g_version` build-path string in .data |
| nucleo-f072rb:nsh (Cortex-M0, DEBUG_NOOPT) | 86839 | 86851 | +12 (+8 text)
| M0 has no 32x32->64 multiply instruction, so `__aeabi_lmul` is still used |
| nucleo-f072rb:nsh (Cortex-M0, DEBUG_FULLOPT) | ... | ... | ... | ... |
## Testing
- Host test comparing `(uint64_t)(uint32_t)jdn * 86400` against the original
`(int64_t)jdn * 86400` over the full legal range (strided, with edge
values):
1,178,898 checks, 0 mismatches.
- `sim:nsh`: builds, `ostest` exits with status 0, `/proc/uptime` and `date`
behave normally.
Note: sim uses `CONFIG_RTC=y`, so it does not execute `clock_basetime()`;
this is a
no-regression check only, and the arithmetic is covered by the host test
above.
- Built breadxavr:nsh, stm32vldiscovery:nsh, nucleo-f072rb:nsh
(arm-none-eabi-gcc 14.2.1).
- `tools/checkpatch.sh -c -u -m -g HEAD~1..HEAD` clean.
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