>> In some cases, you want to re-execute the instruction. A simple >> example is "FPU disabled" on architectures that have such a notion, >> eg for lazy FPU switching. > Weâ??re not talking about lazy FPU switching hereâ?? weâ??re talking about p$
(Or timing. Yes.) A better example might be turning on denormalized-result exceptions (does 754 specify them? I'm fairly sure I've seen at least one FPU that's documented to support them) with a handler that handles them by setting a global flag, disabling the exception, and re-executing the instruction, so as to note that a denormal occurred but otherwise proceeding with the computation. >> On others, like the VAX, [advancing over an instruction is] a right >> pain to do in software. > Iâ??m not particularly concerned about VAX in this case; it doesnâ??t > have IEEE 754 floating point, so all bets are off :-) 68k, then, or x86 - anything with 754 FP and CISCy enough to have variable-sized instructions. The VAX just happens to be the CISC architecture I know best. /~\ The ASCII Mouse \ / Ribbon Campaign X Against HTML [email protected] / \ Email! 7D C8 61 52 5D E7 2D 39 4E F1 31 3E E8 B3 27 4B
