Re: Problem when computing the power of huge numbers

Diego Alexander Rojas <[email protected]> writes:

> Hi,
>
> I've been recently following the book Structure and Interpretation of computer
> programs and I found something very strange. I currently have this two
> functions to compute an exponential function:
>
> (define (even? n)
>   (= (remainder n 2) 0))
>
> (define (square x) (* x x))
>
> (define (fast-exp b n)
>   (cond ((= n 0) 1)
>         ((even? n) (square (fast-exp b (/ n 2))))
>         (else (* b (fast-exp b (- n 1))))))
>
> (define (exp-iter b n sol)
>   (cond ((= n 0) sol)
>         ((even? n) (exp-iter (square b) (/ n 2) sol))
>         (else (exp-iter b (- n 1) (* b sol)))))
> (define (myfast-exp b n)
>   (exp-iter b n 1))
>
> both give different results both non are the correct one (I checked
> with python,
> octave and calc). However this functions just start to fail when computing
> very big exponentials, because it didn't fail with numbers such as
> 123 ^ 331

Could you give a few more details, like an example of where it does
fail?

-- 
Cheers =8-} Mike
Friede, Völkerverständigung und überhaupt blabla