strength reduction

An optimisation where a function of some systematicallychanging variable is calculated more efficiently by usingprevious values of the function. In a procedural languagethis would apply to an expression involving a loop variableand in a declarative language it would apply to the argumentof a recursive function. E.g.

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

==>

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

Here the expensive operation (2**x) has been replaced by thecheaper 2*z in the recursive function f'.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

单词	strength reduction
释义	strength reduction strength reduction An optimisation where a function of some systematicallychanging variable is calculated more efficiently by usingprevious values of the function. In a procedural languagethis would apply to an expression involving a loop variableand in a declarative language it would apply to the argumentof a recursive function. E.g. f x = ... (2x) ... (f (x+1)) ... ==> f x = f' x (2x)wheref ' x z = ... z ... (f' (x+1) 2z) ... Here the expensive operation (2x) has been replaced by thecheaper 2z in the recursive function f'. This maintains theinvariant that z = 2**x for any call to f'.
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