Your first one is essentially similar to demerphq's suggestion at Re: Eek! goto?--which you quite possibly didn't see as I managed to create two root nodes that despite my considering one for deletion, both continue existing.

The other two are neat, but do you need splice in the latter? Wouldn't this work?

   for (0 .. $len-1) {
     $$targ_shift[$_] += $k[$targ_shift[$_+1]] << $shift;
   }
[download]

The downside is speed. If you look at the original C-code you'll see that the whole reason for the switch was to allow a loop to be unwound for performance reasons. In the end, pfaut's realisation that basically the code is unpacking an unsigned long int which lead to the sub hash2() as shown at Re: Re: Eek! goto? using unpack. It came out hands-down winner for performance and I went with that in the end.