sjs@jcricket.ctt.bellcore.com (Stan Switzer) (11/09/88)
In article <398@babbage.acc.virginia.edu> mac3n@babbage.acc.virginia.edu (Alex Colvin) writes: > Charles Simmons may remember the GE635's GTB (Gray to Binary) instruction, > which executes a long chain of XORs, used to convert radar data to binary. > We had real trouble coming up with another use for this. Maybe Hypercube > routing? GTB could be used to compute the parity of a word, and if you really worked at it you could probably figure out how to use it for fast CRCs. If you need to convert Gray code to binary, it's nice to have around since otherwise you are in for a lot of XOR operations (actually, you could use tables to speed it up quite a bit). What I always wondered was why they had a GTB instruction but no BTG instruction. One day I decided to investigate this and found that while converting Gray to binary is a quite a bit of work, converting binary to Gray is a snap: just shift right one and XOR. Stan Switzer sjs@ctt.bellcore.com