CODEWITHSUNDEEP
c++lock-free
Eloff
Eloff

Reputation: 21678

hardware support for atomic fetch-and-add vs fetch-and-or

It seems fetch_add is a win (see post comments as well) against a CAS loop on CPUs that support both.

When toggling clear bit(s) to set bit(s) you can use either a bitwise or or an addition operation. The results will be identical. I expect performance for each would be equal. So the decision on which operation to use would hinge on the differences in hardware support for the operations (if any, I failed to turn up any information on relative processor support.)

Is there any reason to prefer one over the other in this case?

Upvotes: 0

Views: 2179

Answers (1)

Daniel Trebbien
Daniel Trebbien

Reputation: 39208

What you might want to do, instead of coding for a specific processor architecture, is to use a compiler intrinsic. GCC and Clang, for example, support several atomic builtins, one of which is __sync_fetch_and_or.

Since Visual Studio 2005, Visual C++ has supported _InterlockedOr on all architectures.

Upvotes: 1

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