strength reduction from FOLDOC

strength reduction

An optimisation where a function of some systematically changing variable is calculated more efficiently by using previous values of the function. In a procedural language this would apply to an expression involving a loop variable and in a declarative language it would apply to the argument of a recursive function. E.g.

 f x = ... (2**x) ... (f (x+1)) ...

 	==>

 f x = f' x (2**x)
       where
       f ' x z = ... z ... (f' (x+1) 2*z) ...

Here the expensive operation (2**x) has been replaced by the cheaper 2*z in the recursive function f'. This maintains the invariant that z = 2**x for any call to f'.

Last updated: 1995-01-31

Nearby terms:

stream-oriented ♦ STREAMS ♦ strength reduction ♦ STRESS ♦ stress testing

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