The compiler inlines the call to `aux` in `fib2` because that call is readily apparent. It's not so apparent in the other cases that the function `aux` is always called.
At Wed, 27 Apr 2016 06:42:03 -0700 (PDT), Jerry Jackson wrote: > Hello all, > > I was experimenting a bit yesterday and discovered something that surprised > me. Here are two fibonacci functions: > > (define fib1 > (letrec ([aux (lambda (i n) > (if (< n 2) > 1 > (+ (fib1 i (- n 2)) (fib1 i (- n 1)))))]) > (let ([funs (vector aux aux)]) > (lambda (index num) > ((if (= index 0) aux (vector-ref funs index)) index num))))) > > (define fib2 > (letrec ([aux (lambda (i n) > (if (< n 2) > 1 > (+ (fib2 i (- n 2)) (fib2 i (- n 1)))))]) > (let ([funs (vector aux aux)]) > (lambda (index num) > (if (= index 0) > (aux index num) > ((vector-ref funs index) index num)))))) > > I expected them to behave basically identically (in fact, I thought they > would > probably generate the same code). However, that was not the case: > > > (time (fib1 0 40)) > cpu time: 4490 real time: 4489 gc time: 0 > 165580141 > > (time (fib1 1 40)) > cpu time: 5031 real time: 5027 gc time: 0 > 165580141 > > (time (fib2 0 40)) > cpu time: 3042 real time: 3040 gc time: 0 > 165580141 > > (time (fib2 1 40)) > cpu time: 5031 real time: 5027 gc time: 0 > 165580141 > > (time (fib1 0 40)) > cpu time: 4535 real time: 4532 gc time: 0 > 165580141 > > (time (fib2 0 40)) > cpu time: 3027 real time: 3025 gc time: 0 > 165580141 > > > > It looks like one of the functions is 1.5 times faster than the other (in the > i == 0 case). Any ideas as to why? > > Thanks, > --Jerry Jackson > > -- > You received this message because you are subscribed to the Google Groups > "Racket Users" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to racket-users+unsubscr...@googlegroups.com. > For more options, visit https://groups.google.com/d/optout. -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
