// Both a and b are odd. Assume a > b; then gcd(a - b, b) = gcd(a, b).
      // But in gcd(a - b, b), a - b is even and b is odd, so we can divide out powers of two.

      // We bend over backwards to avoid branching, adapting a technique from
      // http://graphics.stanford.edu/~seander/bithacks.html#IntegerMinOrMax

      long delta = a - b; // can't overflow, since a and b are nonnegative

things, all because they WOULD not remember the simple rules
their friends had taught them:  such as, that a red-hot poker
will burn you if you hold it too long; and that if you cut your
finger VERY deeply with a knife, it usually bleeds; and she had
never forgotten that, if you drink much from a bottle marked
`poison,' it is almost certain to disagree with you, sooner or
later.

  However, this bottle was NOT marked `poison,' so Alice ventured

      // Both a and b are odd. Assume a > b; then gcd(a - b, b) = gcd(a, b).
      // But in gcd(a - b, b), a - b is even and b is odd, so we can divide out powers of two.

      // We bend over backwards to avoid branching, adapting a technique from
      // http://graphics.stanford.edu/~seander/bithacks.html#IntegerMinOrMax

      int delta = a - b; // can't overflow, since a and b are nonnegative

things, all because they WOULD not remember the simple rules
their friends had taught them:  such as, that a red-hot poker
will burn you if you hold it too long; and that if you cut your
finger VERY deeply with a knife, it usually bleeds; and she had
never forgotten that, if you drink much from a bottle marked
`poison,' it is almost certain to disagree with you, sooner or
later.

  However, this bottle was NOT marked `poison,' so Alice ventured