Achieving reliable reproducibility for floating point calculations is... difficult, to say the least. There are minor differences between hardware (x87 vs SSE i

Achieving reliable reproducibility for floating point calculations is... difficult, to say the least. There are minor differences between hardware (x87 vs SSE is the most famous one, but there are others). Changing compiler, its version or options may produce subtly different results (the most obvious example is the -ffast-math flag). And even the bigger problem is implementation of non-primitive (e.g. trigonometric) functions. Usually your program will use implementation from a system or vendor library, which probably have different underlying implementations.