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Win32 SystemTimeToFileTime

by ZlR (Chaplain)
on Jan 19, 2005 at 12:45 UTC ( #423356=sourcecode: print w/replies, xml ) Need Help??
Category: Win32 Stuff
Author/Contact Info ZlR

This is a perl 5.6 function that will do a SystemTimeToFileTime conversion, without using Win32::API.

The FileTime is an internal win32 date format described by microsoft as "a 64-bit value representing the number of 100-nanosecond intervals since January 1, 1601 (UTC)" .

This function takes for argument a time in the form of a ($sec,$min,$hour,$mday,$mon,$year) list and returns the equivalent date in the Filetime format.

In my case this was usefull to write computed times into the registry, which allowed to control start and stop times of some windows functions and services . For this reason the result is a coma separated list which was expected by the registry. Join the result if you need the "raw" Fileformat

Note that this code works for Perl 5.6 , which Math::BigInt lacks proper hex conversion functions : thanks a lot to ysth for the 5.6 equivalent as the as_hex() . Also thanks to this post for the as_int :)

use Time::Local ;
use Math::BigInt ;

sub SysToHex {

    my ($sec,$min,$hour,$mday,$mon,$year)= @_ ;
    my $sectime = timegm($sec,$min,$hour,$mday,$mon,$year) ;
    my @hexReg1601  ;  # Result
    # Conversion to intervals of 100 nanosecondes since 1970 
    my $secsystime = Math::BigInt -> new( $sectime )  ;
    my $nano100= Math::BigInt -> new(10000000)  ;
    my$nanosecsys = $secsystime -> bmul ( $nano100 ) ;
    # 100 ns intervals since 1601 and 1970
    # obtained within windows by manualy
    # entering the date 01/01/1970
    my $hex1970 = '0x019DB1DED53E8000' ;
    my $nano1970 = X2I ( $hex1970 ) ;
    # Total number of 100ns intervals
    my $sec1601 = $nano1970 + $nanosecsys ; 
    my $hex1601 = I2X ( $sec1601) ;
    # This coma separated format is expected by the registry
    my @liste1601 = split ( "", $hex1601 ) ;
    unshift (@liste1601, "0" ) unless ( @liste1601 % 2 == 0 )  ;
    while (@liste1601)  { 
    push ( @hexReg1601, splice (  @liste1601, -2 ), "," ) 
    pop @hexReg1601 ; # Gets rid of the last coma
    return join ( "", @hexReg1601 ) ;


sub X2I {
    my $n = shift;
    $n = '0' x (4 - (length($n) % 4)) . $n;
    my $m = Math::BigInt->new(0);
    while ( my $o = substr($n, 0, 4, '') ) {
        $m = $m * 65536 + hex $o;

sub I2X {
    my $i = shift;
    my $hex = '';
        do {
        my $mod = $i % 16;
        $hex .= sprintf("%x", $mod);
        } while $i = $i / 16;
        scalar reverse $hex;
Replies are listed 'Best First'.
Re: Win32 internal time format : SystemTimeToFileTime
by theorbtwo (Prior) on Jan 19, 2005 at 21:28 UTC

    BTW, windows uses a whole hodge-podge of time formats in various places, to call this one more internal then the rest is likely incorrect.

    Warning: Unless otherwise stated, code is untested. Do not use without understanding. Code is posted in the hopes it is useful, but without warranty. All copyrights are relinquished into the public domain unless otherwise stated. I am not an angel. I am capable of error, and err on a fairly regular basis. If I made a mistake, please let me know (such as by replying to this node).

      hmm, ok, corrected :)
      Just to add something, this "FILETIME" is the format used to track file times (duh) but it was also used in the registry to do something completly different : hodge-podge !!

Re: Win32 SystemTimeToFileTime
by zentara (Archbishop) on Jan 20, 2005 at 11:46 UTC
    representing the number of 100-nanosecond intervals since January 1, 1601 (UTC)"

    I wonder why they chose 1601?

    I'm not really a human, but I play one on earth. flash japh

      Perhaps because it's the first new century after the adoption of the Gregorian calender.

      Examine what is said, not who speaks.
      Silence betokens consent.
      Love the truth but pardon error.

      err, my words when i saw it !
      Maybe it's an hidden tribute to Robert Devereux and the essex rebellion ?

      Here is also a discussion on time formats.
      They call it the "win32 epoch".

      This thread here offers another (somehow more magical) solution, but i don't think it would work with perl 5.6 .


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