Question

I have this code:

__asm jno no_oflow
overflow = 1;
__asm no_oflow:

It produces this nice warning:

error C4235: nonstandard extension used : ‘__asm’ keyword not supported on this architecture

What would be an equivalent/acceptable replacement for this code to check the overflow of a subtraction operation that happened before it?

Answer 1

First define the following:

#ifdef _M_IX86
typedef unsigned int READETYPE;
#else
typedef unsigned __int64 READETYPE;
#endif

extern "C"
{
READETYPE __readeflags();
}

#pragma intrinsic(__readeflags)

You can then check the eflags register as follows:

if ( (__readeflags() & 0x800))
{
    overflow = 1;
}