Il 11 dicembre 2023 alle 20:24 Folsk Pratima ha scritto:
Also, the fact that the code runs forever nonetheless is very sad, because C equivalent taken from wiki[1] calculates the whole things almost immediately. The C code is ultra simplified:
#include
#include int IsPrime(int64_t n) { if (n == 2 || n == 3) return 1; if (n <= 1 || n % 2 == 0 || n % 3 == 0) return 0;
for (int i = 5; i * i <= n; i += 6) { if (n % i == 0 || n % (i + 2) == 0) return 0; }
return 1; }
int main () { printf ("1506491439391566589: %d\n", IsPrime (1506491439391566589)); }
Let’s implement the algorithm in Haskell, shall we? import System.Environment isPrimeWiki :: Integer -> Bool isPrimeWiki 2 = True isPrimeWiki 3 = True isPrimeWiki n | n <= 1 || rem n 2 == 0 || rem n 3 == 0 = False isPrimeWiki n = let f i | i^2 > n = True | rem n i == 0 || rem n (i+2) == 0 = False | otherwise = True in f 5 main :: IO () main = do [n] <- getArgs print $ isPrimeWiki (read n) then f@x270:/tmp/prova$ time ./prime 1506491439391566589 True real 0m0.014s user 0m0.001s sys 0m0.005s