Re: encode-time vs decode-time

[Paul Eggert <eggert@cs.ucla.edu>]

Adam Porter wrote:
> I'm curious, is Emacs fast enough or consistent enough to make use of
> high-resolution timestamps anyway?  I guessed that, with GC pauses,
> etc., it wouldn't be a suitable platform for such calculations in
> real-time.  Although I guess if the timestamps were from outside Emacs,
> one could operate on them anyway.

You're right that calling (current-time) from Elisp won't give you nanosecond 
accuracy; on my platform, just calling that function takes a few hundred 
nanoseconds so some error is inherent. You're also right that Emacs isn't 
suitable for hard real-time applications.

As you mention, a common use for Emacs timestamps is to process times generated 
outside Emacs itself, e.g., file timestamps. On typical POSIXish platforms, file 
timestamps have nanosecond resolution and range from -2**63 to 2**63 seconds 
after the epoch, and Emacs can handle all of these timestamps though a few 
functions like decode-time will probably fail due to limitations of the 
underlying C libraries.