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That is, >> >> (1 << (n - 1)) * 2 - 1 <==> >> 2^(n-1) * 2^1 - 1 = (by rule of exponents) >> 2^n - 1 <==> >> (1 << n) - 1. > > ...except when n==64 (for the actual code below), in which case the > result of the shift becomes undefined. Oh, right, for bit 63 being set. Forgot about that one. Good call. Thanks, Luben