A confusing bit of code. YMMV.

confounding.pl

# A few things have been renamed in an attempt to protect the innocent (and guilty)

package SomePackage;

use SomePackage;

sub LoadUnits {
    return if $ser{'m'};
    my($file) = "$SomePackage::HOME/etc/serunits.conf";
    open(SERUNITS,"<$file") || return; 
    local ($_);  # So we don't clobber our caller's $_
    while (<SERUNITS>) {
        /^\s*#/ && next;  /^\s*$/ && next;
        chop; 
        my($a,$t,$x,$p,$n,$s) = split(':',$_);
        my($m,$o,$u) = $x=~/^([-+]?\d*\.?\d*)?([-+]\d*\.?\d*)?\s*(.*)\s*$/;
        $ser{$a} = $_;
        $serm{$a} = ($serm{$u}||1)*($m || 1);
        $sero{$a} = $o * $serm{$u} + $sero{$u};
        foreach (split(/[,\s]+/,$s)) { $_ && ($unittab{"$_ $t"}=$a); }
    }
    close(SERUNITS);
}

sub Conv {
    my($f,$t,@v) = @_;
    unless ($ser{'m'}) { LoadUnits(); }
    my($fm,$fo,$fa) = $f=~/^([-+]?\d*\.?\d*)?([-+]\d*\.?\d*)?\s*(.*)\s*$/;
    my($tm,$to,$ta) = $t=~/^([-+]?\d*\.?\d*)?([-+]\d*\.?\d*)?\s*(.*)\s*$/;
    $tm=$tm||1; $fm=$fm||1;
    $ser{$fa} || return;
    my($fd,$ft,$fx,$fp,$fn,$fs,$ff) = split(':',$ser{$fa});
    my(%f) = SomePackage::URLDecode($ff);
    $ta = $f{$ta} if $f{$ta};
    if (!$ser{$ta}) { $ta = $unittab{"$t $ft"}; }
    my($td,$tt,$tx,$tp,$tn,$ts,$tf) = split(':',$ser{$ta} || $ser{$fa});
    my($mult,$offs) = (1,0);
    if ($ser{$ta} && $ft eq $tt && $fa ne $ta) { 
        $mult=$serm{$fa}/$serm{$ta}; 
        $offs=($sero{$fa}-$sero{$ta})/$serm{$ta}; 
    }
    $offs = $to + ($offs-$fo*$mult)/$tm; $mult *= $fm/$tm;
    @f{qw(fabbr tabbr type mult offs fname fsrc tname tprec)} =
        ($fa,$ta || $fx,$ft,$mult,$offs,$fn,$fs,$tn,$tp);
    foreach(@v) { 
        /^\s*$/ && (push @{$f{'v'}},'NA') && next;
        if (($fm,$fo,$fa) = /^([-+]?\d*\.?\d*)([-+]\d*\.?\d*)?\s*(.+)\s*$/) {
            ($fd,$ft,$fx,$fp,$fn,$fs,$fw,$ff) = split(':',$ser{$fa});
            if ($ft eq $tt) { 
                push @{$f{'v'}}, $fm*$serm{$fa}/$serm{$ta} + 
                    ($sero{$fa}-$sero{$ta})/$serm{$ta} + $fo;
                next;
            }
        }
        push @{$f{'v'}}, (/^\s*[+-]?\.?\d/) ? $_ * $mult + $offs : $_; 
    }
    @{$f{'fv'}} = map { sprintf("%.*f", $f{tprec}, $_) } @{$f{'v'}};
    (wantarray && @v!=1) ? %f : $f{'v'}[0];
}

1;