I have seen people use addition where a bitwise OR would be more conceptually appropriate, because they believe it is faster. Is this true? If yes, do all modern compilers know this trick?
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I have seen people use addition where a bitwise OR would be more conceptually appropriate, because they believe it is faster. Is this true? If yes, do all modern compilers know this trick?
“Conceptually appropriate” and “faster” are two different things. The former is semantics, while the latter often involves breaking semantics.
As for the question in the title, there’s very little (if any) difference speedwise. A compiler for a CPU where this actually happens, will usually optimize it anyway — if it doesn’t cause different results, which it very well can and usually will.
Write your code correctly — if you mean to OR, then OR. If the add-vs-OR ends up being faster, either your compiler will do it for you or you can change it later after you’ve decided whether the potential extra half-nanosecond per iteration is worth the cost in readability and the bugs such a change might cause.