Fractional part of epoch - perl

Question

I have an epoch value of 1372252864.901871 which needs to be converted to localtime in perl. I know that localtime($val) where $val is set to 1372252864.901871 converts the value to local time. But I also need to add values of 100 msecs or say 86.7 msecs to this and determine the computed local time. How do I do this? Does the function localtime() take care of fractional epoch value that I have given?

Answer 1

If you just want to add to an epoch time and get another epoch time, just do:
1372252864.901871 + .0867
If you are doing something else, no, localtime does not preserve fractional seconds. You probably want to use DateTime to deal with fractional seconds:
use DateTime;
my $time = DateTime->from_epoch(epoch=>1372252864.901871, time_zone=>'local');
$time->add(nanoseconds=>86.7e6);
print $time->epoch + $time->nanosecond / 1e9;
(time_zone isn't needed for this example, but sounds like what you might want for other things you might be doing with this time)

Answer 2

You might want Time::HiRes:
The Time::HiRes module implements a Perl interface to the usleep,
nanosleep, ualarm, gettimeofday, and setitimer/getitimer system calls,
in other words, high resolution time and timers

Answer 3

The localtime function breaks down a raw time like 1372252864 into year, month, day, etc. Any fractional part of the raw time is quietly ignored.
I'm not aware of any function, either built-in or in a module, that supports broken-down times with a resolution finer than 1 second.
But since you already have the fractional seconds, I'd say you can already do what you need to do. Just use localtime (or gmtime) to break down the integer part of your raw timestamp, and then take the fractional part:
$timestamp = 1372252864.901871;
#parts = localtime($timestamp);
$fraction = $timestamp - int($timestamp);
$milliseconds = int($fraction * 1000.0);
It should be easy enough to write your own high-resolution replacement for localtime that does this for you.
If you need to add 86.7 milliseconds to a timestamp, you'll need to use the raw form anyway:
$timestamp = 1372252864.901871;
$timestamp += 86.7/1000.0;

Answer 4

The simplest way that occurs to me is to use Time::HiRes::Value to handle arithmetic on times to 1μs accuracy, and Time::Piece to format the result as a date/time string.
Time::HiRes::Value holds the time as a two-element array; the first field has the whole seconds while the second has the number of microseconds. That's the same format that Time::HiRes functions work with, but there's nothing that I know of that will natively convert to a date/time string so I've used Time::Piece to convert the whole seconds and just appended the fractional seconds.
It looks like this
use strict;
use warnings;
use Time::HiRes::Value;
use Time::Piece;
my $dt = Time::HiRes::Value->new(1372252864.901871);
my $delta = Time::HiRes::Value->new(86.7E-3); # 86.7ms
$dt += $delta;
print dt_to_string($dt), "\n";
sub dt_to_string {
my ($dt) = #_;
Time::Piece->new($dt->[0])->datetime =~ s{(\d+)\z}{$1 + $dt->[1] / 1E6}er;
}
output
2013-06-26T14:21:4.98857