On 21 May 2014 07:34, Robin Vowels <robi...@dodo.com.au> wrote: > From: "Ed Jaffe" <edja...@phoenixsoftware.com> > Sent: Wednesday, May 21, 2014 2:52 PM > > > > On 5/20/2014 8:44 PM, Robin Vowels wrote: >> >>> >>> I use MVCL a lot even for very small moves where the length is not >>>> known at assembly time. But I know my environment and its performance >>>> requirements, and often judge the relative elegance, generality, and >>>> programmer-readability of such an instruction to override what small >>>> performance gain there might be to multipathing and/or loops. >>>> >>> >>> Sounds like overkill. >>> MVC with EX would be simpler. >>> >> >> Not if you want padding. >> > > You didn't mention padding. Only small moves. > > But even when padding is required, you can move the padding byte into the > destination area first. >
At last resort one looks at the alternatives. The code I inherited has lots of EX MVC (into static areas near the code even) but the area is too crowded that I dare to free up the 4 right registers and change it. Recently for some new code doing memory allocations, I was very pleased with a MVCL. Rather elegant to have one instruction that copies the prepared header into the block and wipes the payload with padding.Reading the Principles of Operation last night, I noticed it states that some models may be very good in doing MVCL. But probably also in MVC overlaps by one byte, maybe even EX of those... Rob
