This report is meant to prompt discussion, if desired, on the advisability of distinguishing new files from old using subsecond data. (It isn't clear to me that it is important to do this.)

Some file systems keep sub-second modification times, but the number of seconds since the epoch grows to a very large number, and given the limited number of significant bits in floating point numbers, it's important to carry out this comparison carefully (or use some new integer data) so newly created files don't appear to be older than their source files due to rounding and other conversion anomalies. Current floats don't have the precision to hold both the number of seconds since the epoch and a nanosecond precision fractional second.