On Mon, Apr 8, 2013 at 9:34 PM, Bradley Lucier <luc...@math.purdue.edu>wrote:
> (define (iota m n) > (let loop ((result '()) > (n (- n 1))) > (if (<= m n) > (loop (cons n result) > (- n 1)) > result))) > > (define (partial-factorial m n) > ;; computes the product (m+1) * ... * (n-1) * n > (if (< (- n m) 10) > (apply * (iota (+ m 1) (+ n 1))) > (* (partial-factorial m (quotient (+ m n) 2)) > (partial-factorial (quotient (+ m n) 2) n)))) > > (define (factorial n) > (partial-factorial 0 n)) > > In Gambit, even in the interpreter, this is pretty fast: > > (define a (time (factorial 1000000))) > (time (factorial 1000000)) > Indeed, it's impressively fast! % racket fast-factorial.rkt cpu time: 5760 real time: 5771 gc time: 28 Probably this should replace the default factorial version then. Laurent
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