3 ms·
I do know x86 for example has things like the STOS/STOSB/STOSW/STOSD which specifies a lot of behavior for a single instruction, and combined with the REP prefi
by tenebrisalietum 5y ago
I do know x86 for example has things like the STOS/STOSB/STOSW/STOSD which specifies a lot of behavior for a single instruction, and combined with the REP prefixes is a pretty elegant way to do memory block operations. I don't think 68000 had anything like that.
- JoeAltmaier 5y agoTo be fair, Intel nerfed those instructions for a long time. See, DOS was using REPNZ STOSW for timing things. So as the processors got faster, those instructions didn't, so as to make DOS BIOS continue to operate correctly. It was a terrible time for x86. At the same time, I used a clever 12-byte sequence of those opcodes to swap software interrupt vectors on process switch. So each process could have its own floating-point exception handlers etc. We called it the 'soft vector chain' and it was among the least known parts of our kernel. A colleague (John McGinty) suggested in our old age we could consult by scratching our beards and saying "Ah! It must be the soft vector chain!" for every problem.