Reading the System Clock
There are two interesting numbers here, the precision of the clock and the time it takes to read the clock. These serve as a floor to the jitter component. This also helps to make sure we don't divide by zero...
DLM says that the next leap forward on lowering the floor will happen when it takes less than 100nsec to read the clock.
is the time it takes to read the clock in nanoseconds (it's an integer type), and
is the same thing in a floating type but in usec.
is log2 of
Some systems have
and it behaves differently on different OSes. NTP generally uses
for its operations, but on some OSes that value will not give use the information we want: