Question

How can I properly store n in functions like the following one ? Because of value in n changes for some reason after I use it once.

function Test(n: Integer): Byte;
asm
  mov eax, n
  add eax, eax
  add eax, n
  mov ecx, eax
  mov ebx, eax
  mov ecx, n
end;

Answer 1

The first argument to the function, n, is stored in eax, so your line

mov eax, n

is highly strange (move n to n). Also, if you change eax, you change n.

You could save the argument for future use (since you likely need to alter eax):

var
  tempN: integer;
asm
  mov tempN, eax

Also, IIRC, you must not change the value of ebx when writing inline ASM. Hence, you need to surround your code by push ebx and pop ebx.