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[H.G.Muller]

Indeed, for division by a constant multiplication with the reciprocal seems the obvious choice. More tricky is the case where you have to divide through a variable unknown at compile time.

The best way to do that would be to make use of the SSE (or 3DNow!) reciprocal instruction, (a fast table lookup), followed by two or three iterations of x = x*(2-n*x) to obtain 1/n.