Strength reduction
|
|
Strength reduction is a compiler optimization where a function of some systematically changing variable is calculated more efficiently by using previous values of the function. In a procedural programming 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)) ...
becomes
- 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Here the expensive operation (2**x) has been replaced by the cheaper 2*z in the recursive function f'.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'.
- This article was originally based on material from the Free On-line Dictionary of Computing, which is licensed under the GFDL.