HP Forum Archive 05

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Rapid Reverse Branching Message #1 Posted by Steve (Australia) on 26 Dec 2000, 5:40 p.m. Can someone explain "Rapid Reverse Branching" as it exists on the HP67/97? I remember the reference to it in perhaps the HP41 card reader manual or maybe a copy of PPC with a program, but I could never find an explanation. Now it's popped up in another thread it has reminded me of something I have waited almost 20 years to get explained.

Re: Rapid Reverse Branching Message #2 Posted by Mike Hicks on 26 Dec 2000, 9:56 p.m., in response to message #1 by Steve (Australia) Steve, There is a section in the museum for HP-67/97 Programming called Rapid Reverse Branching. I have not used the technique and cannot explain further. Good Luck. Mike

Re: Rapid Reverse Branching Message #3 Posted by Nenad Vulic (Croatia) on 27 Dec 2000, 11:00 a.m., in response to message #1 by Steve (Australia) Rapid reverse branching in a HP-67/97 program means just this: if you use a GTO(i) instruction (indirect go to) and the number in the I-register is negative, the program continues execution at the program step determined by this number in I-register (say nnn) which lies nnn steps above the step which contains the subject GTO(i) instruction (ie. moves nnn steps before the current step in "reverse" direction). As the machine does not have to search the whole program space for labels, this procedure is fast (so it is called "rapid") and executes much faster than in case of positive nnn (when the program jumps to label "nnn"). This is a kind of addressing by which you may reach any step of program memory and continue execution from there. In this sense, the step that comes before step 001 is the last step, ie. step 224.

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