$c=00000000, $hash=03FFFFFF => $hash=FFFFFFFF   32-bit Perl
$c=00000000, $hash=03FFFFFF => $hash=FBFEFFC1   64-bit Perl
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That doesn't fix the problem, even if you fix the two bugs you introduced. Quote perlop,

The result of overflowing the range of the integers is undefined because it is undefined also in C.

($hash << 6) should be (($hash & 0x03ffffff) << 6)
($hash << 16) should be (($hash & 0x0000ffff) << 16)

Update: My original counter example was bad. Fixed.