Trapdoors

[Phil Karn]

A bit count instruction would be very handy in a project I've been
working on lately, which is a new packet radio link level protocol
for amateur packet radio. This protocol uses forward error correction,
so it needs a highly reliable way to delimit the start of each
physical link frame. A pseudo-random "sync" sequence is the standard
way to do this, and you detect it with a correlator. The bit count
instruction would come in handy here, since the only other fast
way to do it is to use table lookup.

Phil