use strict;
use warnings;
use Date::Manip;
use Date::Calc qw(Add_Delta_DHMS);
use Benchmark qw(cmpthese);

Date_Init ("TZ=UT");

my @dates = ("2007-04-30 12:50:00", "2007-04-30 11:50:00");

print "Manip result: \n", join "\n", manip (), "\n";
print "Calc result: \n", join "\n", calc (), "\n";

cmpthese (-1,
    {
    manip => \&manip,
    calc => \&calc,
    });


sub manip {
    my @results;
    
    for (@dates) {
        my $date = $_;
        my $hour = (split /:/, $date)[0];

        die "Can't find hour" unless $hour =~ /\s(\d{2})$/;

        if ($1 >= 12){
            $date=DateCalc("$date","+24 hours"); ###Takes 2min out of 2:30min.
            $date=&UnixDate($date,"%Y-%m-%d");
        }
        
        push @results, $date;
    }
    
    return @results;
}


sub calc {
    my @results;
    
    for (@dates) {
        my $date = $_;
        my $hour = (split /:/, $date)[0];

        die "Can't find hour" unless $hour =~ /\s(\d{2})$/;

        if ($1 >= 12){
            my ($year,$month,$day, $hour,$min,$sec) =
                $date =~ /(\d{4})-(\d\d)-(\d\d) (\d\d):(\d\d):(\d\d)/;
            ($year,$month,$day, $hour,$min,$sec) = Add_Delta_DHMS (
                $year,$month,$day, $hour,$min,$sec, 1, 0, 0, 0
                );
            $date = "$year-$month-$day $hour:$min:$sec";
        }
        
        push @results, $date;
    }
    
    return @results;
}

##</code><code>##

Manip result: 
2007-05-01
2007-04-30 11:50:00

Calc result: 
2007-5-1 12:50:0
2007-04-30 11:50:00

         Rate manip  calc
manip   662/s    --  -99%
calc  59112/s 8825%    --