Timestamps are often represented as ticks since some epoch, e.g. 1970.01.01
00:00:00, so negative timestamps make sense as times before the epoch - I
meant rounding vs truncating towards 0 vs rounding towards negative
infinite in this sense. Truncating towards negative infinity means that
timestamps are always truncated to an earlier timestamp. Truncating towards
0 would mean that before 1970, timestamps are truncated upwards, which can
lead to similar troubles as the I ones mentioned with rounding. On x86 c++,
when a time_t is divided by an integer, the result is rounded towards 0, so
a naive implementation that uses time_t to represent timestamps can
truncate towards 0, but In impala::TimestampValue, time_ should be the
non-negative nanoseconds since midnight, so it can be simply divided with
1000 to convert from nanoseconds to microseconds.
