I've tried to make this work. I added the implied while loop and put brackets around the 'a' etc. to make it generate lists not strings, but I still can get it to produce the same results as the original. Can you see what I missed?

sub belg4mit {
    my %H;
    my ($len, @k) = @_;
    my ($a,$b,$c) = (0)x3;
    while($len--) {
         $H{(('a')x4,('b')x4,('c')x3)[$len]}
            += $k[$len -1] << (8* ( ($len > 8 ? $len : $len - 1 )%4 ) 
+);
    }
    return ($H{a}||0)+($H{b}||0)+($H{c}||0);
}
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while($len){
  $H{(('a')x4,('b')x4,('c')x3)[--$len]}
  += $k[$len] << (8* ( ($len > 7 ? $len +1 : $len)%4 ) );
}
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This seems to match the output of pfaut's code. If benchmarking you could eek out some more throughput by storing the hash key indexes in an array (as opposed to forcing three x per iteration of the loop.

--
I'm not belgian but I play one on TV.

Might be a bit faster if you throw out the hash and use an array. BTW, I think one of BrowserUK's later posts added back the originally missing low byte of $c so the check for $len > 7 can go, too.

while ($len--) {
    $H[int($len/4)] += $k[$len] << (8 * ($len % 4));
}
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---
print map { my ($m)=1<<hex($_)&11?' ':'';
$m.=substr('AHJPacehklnorstu',hex($_),1) }
split //,'2fde0abe76c36c914586c';
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