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lib: posix: clock: Prevent early overflows

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Algorithm was converting uptime to nanoseconds which can easily
lead to overflows. Changed algorithm to use milliseconds and
nanoseconds for remainder only.

Signed-off-by: Krzysztof Chruscinski <krzysztof.chruscinski@nordicsemi.no>
This commit is contained in:
Krzysztof Chruscinski 2022-01-14 09:25:37 +01:00 committed by Carles Cufí
parent 806cc70f7c
commit 35593ce1e9
1 changed files with 7 additions and 4 deletions
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11
lib/posix/clock.c
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@ -27,7 +27,6 @@ static struct k_spinlock rt_clock_base_lock;
*/
int z_impl_clock_gettime(clockid_t clock_id, struct timespec *ts)
{
uint64_t elapsed_nsecs;
struct timespec base;
k_spinlock_key_t key;
@ -48,9 +47,13 @@ int z_impl_clock_gettime(clockid_t clock_id, struct timespec *ts)
return -1;
}
elapsed_nsecs = k_ticks_to_ns_floor64(k_uptime_ticks());
ts->tv_sec = (int32_t) (elapsed_nsecs / NSEC_PER_SEC);
ts->tv_nsec = (int32_t) (elapsed_nsecs % NSEC_PER_SEC);
uint64_t ticks = k_uptime_ticks();
uint64_t elapsed_secs = k_ticks_to_ms_floor64(ticks) / MSEC_PER_SEC;
uint64_t nremainder = ticks - k_ms_to_ticks_floor64(MSEC_PER_SEC * elapsed_secs);
ts->tv_sec = (time_t) elapsed_secs;
/* For ns 32 bit conversion can be used since its smaller than 1sec. */
ts->tv_nsec = (int32_t) k_ticks_to_ns_floor32(nremainder);
ts->tv_sec += base.tv_sec;
ts->tv_nsec += base.tv_nsec;