sys: timeutil: inconsistent types for local times

[JordanYates]

Describe the bug

The integer types for local times for timeutil conversion functions timeutil_sync_ref_from_local and timeutil_sync_local_from_ref are inconsistent. One presumes the local time is a signed 64bit integer, while the other assume an unsigned 64bit integer.

zephyr/include/sys/timeutil.h

Lines 253 to 254 in cd9421a

	int timeutil_sync_ref_from_local(const struct timeutil_sync_state *tsp,
	uint64_t local, uint64_t *refp);

zephyr/include/sys/timeutil.h

Lines 277 to 278 in cd9421a

	int timeutil_sync_local_from_ref(const struct timeutil_sync_state *tsp,
	uint64_t ref, int64_t *localp);

[pabigot]

This is not a bug. Reference times are defined to be non-negative, hence an unsigned output from timeutil_sync_ref_from_local (negative reconstructed reference times result in a -ERANGE error return).

On the other hand a local time reconstructed from a reference time can be negative, if the reference time corresponds to an event that occurs before the system started.

I'll see if I can tweak the documentation so this is more clear.

[pabigot]

Actually that's already documented in the description:

An interpolated value before local time 0 is provided without error.