Japh algebra, GF(128) edition

[ambrus]

Did you know you could evaluate a polynomial over GF(128) in perl with pack and unpack and tr? Here's how.

sub h {
        $_ = $_[0] = pack b208, 0 . unpack b362, $_[0];
        tr/\0-\c?/\0/;
        tr/\0/\377/c;
        $_
}
for (split //, "k6sNP2B}({ambrusLB%Ox)Z]n0*zf\0I3") {
        $y = $r;
        $v = join $r = '', a .. z;
        $r ^= h($r) & "\217" x 26 ^ h($v) & $y for 0 .. 6;
        $r ^= $_ x 26;
}
print $r;

This code is based on the same idea as Dollar Plus, but written in a different style, so some of the credit goes to martin.

Update: if you prefer one of these unreadable blocks of code, you can of course write this that way too (Update: reformatted blob from four lines to three.)

sub h($){($_=$_[0]=pack b208,0 .unpack b362,$_[0])=~tr/\0-\c?/\0/;tr
/\0/\377/c;$_}do{$y=$r;$v=join$r='',a..z;$r^=h$r&"\217"x26^h$v&$y for
0..6;$r^=$_ x26}for"k6sNP2B}({ambrusLB%Ox)Z]n0*zf\0I3"=~/./g;print$r

Update: removed lots of spaces from end of lines of formatted code.

[BrowserUk]

Could you explain, (or point to an explanation of), (preferably in layman's terms), the annotation "GF(128)"?

I tried a search, but the term matches too many things to know where to start.

[ambrus]

<Reveal this spoiler or all in this thread>

Update: hide all behind spoiler tags.

[BrowserUk]

(The name GF stands for Galois field originally.)

Ah right! Those special French tobacco farms :)

[ambrus]

It's worth to note that the 2012/grothe IOCCC winner by Aaron Grothe, based on David Madore's much older non-obfuscated program (submitted without David's knowledge) does computations with polynomials over GF(256).