Does a c/c++ compiler optimize constant divisions by power-of-two value into shifts?

Question

Question says it all. Does anyone know if the following...

size_t div(size_t value) {
    const size_t x = 64;
    return value / x;
}

...i

Answer 1

Yes, compilers generate the most optimal code for such simplistic calculations. However, why you are insisting specifically on "shifts" is not clear to me. The optimal code for a given platform might easily turn out to be something different from a "shift".

In general case the old and beaten-to-death idea that a "shift" is somehow the most optimal way to implement power-of-two multiplications and divisions has very little practical relevance on modern platforms. It is a good way to illustrate the concept of "optimization" to newbies, but no more than that.

Your original example is not really representative, because it uses an unsigned type, which greatly simplifies the implementation of division operation. The "round towards zero" requirement of the C and C++ languages makes it impossible to do division with a mere shift if the operand is signed.