Fetch-and-add using OpenMP atomic operations

I’m using OpenMP and need to use the fetch-and-add operation. However, OpenMP doesn’t provide an appropriate directive/call. I’d like to preserve maximum portability, hence I don’t want to rely on compiler intrinsics.

Rather, I’m searching for a way to harness OpenMP’s atomic operations to implement this but I’ve hit a dead end. Can this even be done? N.B., the following code almost does what I want:

#pragma omp atomic
x += a

Almost – but not quite, since I really need the old value of x. fetch_and_add should be defined to produce the same result as the following (only non-locking):

template <typename T>
T fetch_and_add(volatile T& value, T increment) {
    T old;
    #pragma omp critical
    {
        old = value;
        value += increment;
    }
    return old;
}

(An equivalent question could be asked for compare-and-swap but one can be implemented in terms of the other, if I’m not mistaken.)

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Fetch-and-add using OpenMP atomic operations

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