On Tue, Apr 9, 2013 at 2:42 PM, Matthew Flatt <mfl...@cs.utah.edu> wrote:
> (for/product ([p (in-range (+ m 1) (+ n 1))]) p) This fact/for variant is a clear winner: > (time (void (fact/for 1000000))) cpu time: 6948 real time: 6956 gc time: 964 > (time (void (factorial 1000000))) cpu time: 9936 real time: 9951 gc time: 3700 > (time (void (fact 1000000))) cpu time: 8445 real time: 8460 gc time: 2273 But I don't fully understand why a simple (for/product ([p (in-range 1 (add1 n))]) p) is as fast as the iota variants. I see that the latter makes many more small products, which are certainly faster, but it also does more products of 2 big numbers, whereas for/product makes only big*small products. Is that a sufficient reason? Laurent
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