Simple double-precision add problem

Hi there.


I've been trying to change my copy of the engine to support double-precision floating-point values in script. So far,so good. Then this issue came up.


Please note the below code:

const char *CodeBlock::exec(U32 ip, const char *functionName, Namespace *thisNamespace, U32 argc, const char **argv, bool noCalls, StringTableEntry packageName, S32 setFrame)
{
...
case OP_ADD:
floatStack[FLT-1] = floatStack[FLT] + floatStack[FLT-1];
FLT--;
break;
...
}


The simple add above is somehow not being processed properly.

If

floatStack[FLT] 32343.235253242525 double
floatStack[FLT-1] 4.5300000000000002 double

then

floatStack[FLT-1], after the add operation above, should be equal to 32347.765253242525. But instead, it's equal to 32347.765625.

Somehow, a significant loss of precision/error has occurred here. And I'm not sure why. After all, if I create a new executable, with just this code:

int main()
{
double rhs=32343.235253242525;
double lhs=4.53;
double result=lhs+rhs;
return 0;
}

lhs 4.5300000000000002 double
rhs 32343.235253242525 double
result 32347.765253242524 double

The above result is exactly what I'd normally expect.

I do know that floatStack[FLT] and floatStack[FLT-1], by default, contain single-precision values cast to double-precision. But nevertheless, this is a simple double-precision add. And I'm only having this strange double-precision add behavior in TGEA 1.8 code, and nowhere else.


I was thinking this had something to do with intrinsic functions begin enabled. On/off, (/iO), makes no difference. /fp:strict, or /fp:precise, makes no difference. I'm still thinking there's a simple answer to this problem that I'm overlooking. I just don't know what it is.


Please help :(

Thanks

Franklin