C inline assembly of x96 fbstp instruction
- by David HUnter
Was wondering how to inline a usage of fbstp on a 32 bit I86 architecture. I tried something like
int main( )
{
double foo = 100.0;
long bar = 0;
asm( "pushl %1; fbstp %0"
: "=m"(bar)
: "r"(foo)
);
...
But bar is unchanged. I have tried reading everything I can find on this but most example simply do things like add two integers together. I can’t find any that talk about pushing operands onto the stack and what I should be doing when an instruction like fbstp writes 80 bits of data back to memory ( i.e. what C type to use ) and how to specify it in the asm syntax.
Also on x86-64 there seems to be a pushq and no pushl but fbstp still exists whereas fbstq does not. Is there some other magic for 64 bit.
