Isn't it called Jump, or more properly, Branch Relative on Condition? Charles
-----Original Message----- From: IBM Mainframe Discussion List [mailto:[email protected]] On Behalf Of Bernd Oppolzer Sent: Monday, February 17, 2014 4:35 PM To: [email protected] Subject: Re: Optimization, CPU time, and related issues Hello, when we discussed the one bit copy topic recently, I had a solution in mind that was kind of inspired by the new "store on condition" instruction, but there was no such solution, because a instruction like "OI on condition" or "NI on condition" would have been necessary, and there are no such instructions. Now my question: I could imagine some use cases for a new instruction, that supresses the execution of the next instruction, depending on certain values of the condition code. For example SKIP NEXT INSTRUCTION IF NOT ZERO, or IF ZERO. This would be much more general than "store on condition", because you could skip every instruction (not only ST), depending on the condition code. Of course, this needs some extensions to the machine logic, because it must be possible that only the PSW will be incremented but the instruction is not executed, depending on this SKIP condition. But: it saves some branches in some cases. My question is: if we had such an instruction, how would this fit into the overall machine concept? And: are there some performance benefits, or are there some problems with this approach, which I do not see? I'm sure, that some historical machines had such concepts ... Kind regards Bernd Am 18.02.2014 00:36, schrieb Ed Jaffe: > > Bottom line: every developer should try to write code that runs as > fast as possible. A single MSU increase at just the wrong time could > translate into huge $$. > ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
