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| author | Gary E. Miller <gem@rellim.com> | 2015-02-11 19:26:03 -0800 |
|---|---|---|
| committer | Gary E. Miller <gem@rellim.com> | 2015-02-11 19:26:03 -0800 |
| commit | 927ce93c49f8a9e84433141357e3602ada077850 (patch) | |
| tree | f58b86a49fa5d565538d6806c56aea67a046ec08 /gpsd.h-tail | |
| parent | c988130851015de651b2632a1f4068c7c3661c1e (diff) | |
| download | gpsd-927ce93c49f8a9e84433141357e3602ada077850.tar.gz | |
Add some comments to TS_NORM()
Diffstat (limited to 'gpsd.h-tail')
| -rw-r--r-- | gpsd.h-tail | 15 |
1 files changed, 13 insertions, 2 deletions
diff --git a/gpsd.h-tail b/gpsd.h-tail index 6436f0bc..85895c5c 100644 --- a/gpsd.h-tail +++ b/gpsd.h-tail @@ -883,7 +883,16 @@ extern void ntpshm_link_activate(struct gps_device_t *); extern void pps_early_init(struct gps_context_t *); #endif /* PPS_ENABLE */ -/* normalize a timespec */ +/* normalize a timespec + * + * three cases to note + * if tv_sec is positve, then tv_nsec must be positive + * if tv_sec is negative, then tv_nsec must be negative + * if tv_sec is zero, then tv_nsec may be positive or negative. + * + * this only handles the case where two normalized timespecs + * are added or subracted. (e.g. only a one needs to be borrowed/carried + */ static inline void TS_NORM( struct timespec *ts) { if ( ( 1 <= ts->tv_sec ) || @@ -894,16 +903,18 @@ static inline void TS_NORM( struct timespec *ts) ts->tv_nsec -= 1000000000; ts->tv_sec++; } else if ( 0 > (ts)->tv_nsec ) { - /* carry from tv_sec */ + /* carry to tv_sec */ ts->tv_nsec += 1000000000; ts->tv_sec--; } } else { /* result is negative */ if ( -1000000000 >= ts->tv_nsec ) { + /* carry to tv_sec */ ts->tv_nsec += 1000000000; ts->tv_sec--; } else if ( 0 < ts->tv_nsec ) { + /* borrow from tv_sec */ ts->tv_nsec -= 1000000000; ts->tv_sec++; } |