{
my @values;
my $prev_first;
my $prev_last;

sub cache {
    my ($data, $first, $last) = @_;

    unless ($prev_first and $prev_last) {
        @values = grep defined, @{$data}{$first .. $last};
    } else {
        for ($prev_first .. $first-1) {
            shift @values if defined $data->{$_};
        }

        for ($prev_last+1 .. $last) {
            push @values, $data->{$_} if defined $data->{$_};
        }
    }

    $prev_first = $first;
    $prev_last  = $last;

    sum(@values) / @values;
}
}

##</code><code>##

        Rate  orig  zaxo   buk  aris cache
orig  6.26/s    --  -22%  -42%  -80%  -98%
zaxo  8.00/s   28%    --  -26%  -75%  -98%
buk   10.9/s   74%   36%    --  -66%  -97%
aris  31.8/s  408%  297%  192%    --  -91%
cache  368/s 5775% 4496% 3283% 1057%    --

##</code><code>##

{
my %cache;
sub cache {
    my $str = shift;

    my ($wday, $mon, $mday, $time, $year) = split /\s+/, $str;
    my ($hour, $min, $sec)                = split ':',   $time;

    my $timebase;

    if ($cache{"$year$mon$mday"}) {
        $timebase = $cache{"$year$mon$mday"};
    } else {
        $timebase = timelocal(0, 0, 0, $mday, $mtrans{$mon}, $year-1900);
        $cache{"$year$mon$mday"} = $timebase;
    }

    return $timebase + $sec + $min*60 + $hour*60*60;
}
}

##</code><code>##

      s/iter  D::P buggy fixed nonre cache
D::P    9.08    --  -76%  -77%  -77%  -92%
buggy   2.16  320%    --   -2%   -3%  -66%
fixed   2.12  328%    2%    --   -2%  -65%
nonre   2.09  335%    4%    2%    --  -65%
cache  0.735 1136%  194%  188%  184%    --