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Strength Reduction
------------------

Strength reduction replaces an expansive operation by a cheaper one, such as
multiplication by addition or subtraction, multiplication instead of
exponentiation; use compound assignment operators such as += wherever possible,
changing code of the form a[i] = a[i] + x to a[i] += x, since they result in
fewer bytecode instructions; use shifts instead of multiplication by powers of
two, etc.

For example:

	x ** 2  = x * x
	2.0 * x = x + x
	x / 2   = x * 0.5


Induction Variable
------------------

A variable is called an induction variables of a loop if every time the variable
changes values it is incremented or decrmented by some constant.
Basic induction variables i whose only assignments within the loop is of the
form i += c, where c is a constant.