> >> Good point well made but can you explain why changing a B to a BE > in a tight loop results in 43% difference? > > But aren't those two completely different cases (even if it is the > same instruction)? The first is an unconditional branch, the second > one a conditional branch. That probably makes a big difference to > the processor. Where I expect the unconditional one to be faster > than the conditional one. > > > > I assume it is 43% faster than the conditional one? If it is the > other way around I will be very surprised as well. > > No. It's the opposite which is why I originally posted. The > unconditional branch is slower and I want to know why.
The relevant comparison is not conditional branch vs. unconditional branch. It is branch not taken vs. branch taken. Sequential execution is always best. Branch prediction tries to mitigate some of the effects of nonsequential execution. Jim Mulder z/OS System Test IBM Corp. Poughkeepsie, NY ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
