Adding floating point/double numbers in assembly
Solution 1
I haven't done x87 assembly in a decade, but it should be something like:
fld num1 ; load num1 and push it onto the fpu stack
fld num2 ; load num2 and push it onto the fpu stack
faddp ; pop two numbers, add them, push sum on the stack
fstp res ; pop sum from the stack and store it in res
Solution 2
The instruction you probably want is ADDSD, but I don't know for sure.
Here's the link to Intel's instruction set manuals. http://www.intel.com/content/www/us/en/processors/architectures-software-developer-manuals.html/
They used to mail you hard copies for free, but it looks like that's no longer true.
Solution 3
You need a different set of instructions to manipulate floating point numbers. Here's an introduction that should help: x86 Assembly: Floating Point
Solution 4
Try this:
_asm{
movq xmm0,[num1]
addpd xmm0, [num2];
movq [res],xmm0
// sse2
}
scrat101
Updated on August 05, 2022Comments
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I am trying to experiment with inline assembly, and I am trying to add decimal numbers (no, NOT integers) in inline assembly. Issue is, when I call the following function:
inline double ADD(double num1, double num2) { double res; _asm{ push eax; push the former state of eax onto stack mov eax, num1; add eax, num2; mov res, eax; pop eax; restore the former state of eax now that we are done } return res;}
The compiler complains of improper operand size at the inline assembly (ALL lines of assembly excluding the push and pop instruction lines). So I have to change to an integer type, such as unsigned long, and then it works, but of course only supports integer types; decimal results are rounded.
Is there any way to add in assembly that allows for decimal results like 8.4?