The function as specified used gettimeofday() which is susceptible
to manual time changes, and is obsoleted in POSIX.1-2008. The
replacement uses clock_gettime(CLOCK_MONOTONIC, ) which is not
susceptible to manual time changes (at least on Linux) and cannot run
backwards.
Also, on systems with 32-bit integers, the value returned by this
function wraps around every 49.7 days. To cope with a wraparound in
a way compliant with the C standard, this value needs to return an
unsigned integer type rather than a signed integer type.
matt335672
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