On Fri, Mar 26, 2010 at 10:46 AM, Rafael Cunha de Almeida
<almeidaraf@gmail.com> wrote:
Hello,
During a talk with a friend I came up with two programs, one written in
C and another in haskell.
Haskell
main :: IO ()
main = print $ rangeI 0 0
rangeK :: Int -> Int -> Int -> Int -> Int
rangeK i j k acc
| k < 1000 =
if i * i + j * j + k * k `mod` 7 == 0
then rangeK i j (k+1) (acc+1)
else rangeK i j (k+1) acc
| otherwise = acc
rangeJ :: Int -> Int -> Int -> Int
rangeJ i j acc
| j < 1000 = rangeJ i (j+1) (acc + rangeK i j 0 0)
| otherwise = acc
rangeI :: Int -> Int -> Int
rangeI i acc
| i < 1000 = rangeI (i+1) (acc + (rangeJ i 0 0))
| otherwise = acc
You might try using bang patterns. It's possible that GHC didn't detect the strictness. Only way I know to check is to look at the core. Use something like ghc-core from Hackage to view it. Ideally the core is using Int# instead of Int and avoiding lots of boxing.
I compiled the haskell code with ghc -O3 and I compiled the C code with
gcc -O3. The execution time of the programs were dramatically different.
You can test it yourselves, but here is the time I've got in my system: