Derek Elkins wrote:
Try with rem instead of mod.
(What the heck is with bottom?)
The bottom was there by error and I was lazy to redo
the tests so I rather posted exactly what I was
doing. I do not know the compiler that good to be
absolutely sure it cannot have impact on result
... so I rather did not doctor what I did :-)
Ok, rem did help quite a bit. Any comments why it is so?
Here are summary of results for those interested. I run
all the tests once again. Haskell was about 13% slower
than C++.
MS cl.exe options: /Ox /G7 /MD
ghc options: -O2
C++ version: 1.000; 0.984; 0.984
Haskell version specialized to Int: 1.125; 1.125; 1.109
Haskell version specialized to Integer: 8.781; 8.813; 8.813
Haskell version specialized to Int64: 9.781; 9.766; 9.831
The code:
% cat b.hs
module Main (divisors, perfect, main) where
import Data.Int
divisors :: Int -> [Int]
divisors i = [j | j<-[1..i-1], i `rem` j == 0]
perfect :: [Int]
perfect = [i | i<-[1..10000], i == sum (divisors i)]
main = print perfect
% cat b.cpp
#include <iostream>
using namespace std;
int main() {
for (int i = 1; i <= 10000; i++) {
int sum = 0;
for (int j = 1; j < i; j++)
if (i % j == 0)
sum += j;
if (sum == i)
cout << i << " ";
}
return 0;
}
%
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