diff options
Diffstat (limited to 'gl/timespec.h')
| -rw-r--r-- | gl/timespec.h | 32 |
1 files changed, 28 insertions, 4 deletions
diff --git a/gl/timespec.h b/gl/timespec.h index 81b342300e..175de7f263 100644 --- a/gl/timespec.h +++ b/gl/timespec.h @@ -22,15 +22,39 @@ # include <time.h> /* Return negative, zero, positive if A < B, A == B, A > B, respectively. - Assume the nanosecond components are in range, or close to it. */ + + For each time stamp T, this code assumes that either: + + * T.tv_nsec is in the range 0..999999999; or + * T.tv_sec corresponds to a valid leap second on a host that supports + leap seconds, and T.tv_nsec is in the range 1000000000..1999999999; or + * T.tv_sec is the minimum time_t value and T.tv_nsec is -1; or + T.tv_sec is the maximum time_t value and T.tv_nsec is 2000000000. + This allows for special struct timespec values that are less or + greater than all possible valid time stamps. + + In all these cases, it is safe to subtract two tv_nsec values and + convert the result to integer without worrying about overflow on + any platform of interest to the GNU project, since all such + platforms have 32-bit int or wider. + + Replacing "(int) (a.tv_nsec - b.tv_nsec)" with something like + "a.tv_nsec < b.tv_nsec ? -1 : a.tv_nsec > b.tv_nsec" would cause + this function to work in some cases where the above assumption is + violated, but not in all cases (e.g., a.tv_sec==1, a.tv_nsec==-2, + b.tv_sec==0, b.tv_nsec==999999999) and is arguably not worth the + extra instructions. Using a subtraction has the advantage of + detecting some invalid cases on platforms that detect integer + overflow. + + The (int) cast avoids a gcc -Wconversion warning. */ + static inline int timespec_cmp (struct timespec a, struct timespec b) { return (a.tv_sec < b.tv_sec ? -1 : a.tv_sec > b.tv_sec ? 1 - : a.tv_nsec < b.tv_nsec ? -1 - : a.tv_nsec > b.tv_nsec ? 1 - : 0); + : (int) (a.tv_nsec - b.tv_nsec)); } void gettime (struct timespec *); |