Hi,

I've been googling but can't find an answer to my question. The Simply FPU tutorial seems a bit vague on the subject. Do I need an FWAIT instruction in this code?



In other words, is there a danger that the third instruction might finish executing before the second one?

Thanks in advance.

afaik the answer to both questions is no

afaik all potential synchronisation conflicts between cpu and fpu are handled automatically in modern processors except where exceptions are raised and flag testing instructions are involved. thats where wait or fwait is needed

here for a conflict to arise the cpu would have to finish the 3rd instruction before the fpu had read the operand data of the 2nd instruction. when the fpu actually finishes the fadd instruction is not critical (except maybe for any subseqent compare instructions handled by the cpu)

but at the end of the day only thorough testing of your code will prove it one way or the other

As nop said, WAIT checks for pending FP exceptions so you don't need it.

WAIT is documented well in offical processor manuals:

http://x86asm.net/links/index.html#Processor-Manuals

But you still need it at compares?

Thanks for clarifying guys.