Is this C++ implementation for an Atomic float safe?

Question

Edit: The code here still has some bugs in it, and it could do better in the performance department, but instead of trying to fix this, for t

Answer 1

Have your compiler generate assembly code and take a look at it. If the operation is more than a single assembly-language instruction, then it's not an atomic operation, and requires locks to operate properly in multiprocessor systems.

Unfortunately, I'm not certain that the opposite is also true -- that single-instruction operations are guaranteed to be atomic. I don't know the details of multiprocessor programming down to that level. I could make a case for either result. (If anyone else has some definitive information on that, feel free to chime in.)