On 7/15/07, Sebastian Sylvan
"unsafe"' here just means direct array indexing. Same as the other languages. Haskell's 'unsafe' is a little more paranoid that other languages.
Yes, I was kindof hoping it was something like that. Cool :-)
Since the goal is to flip bits very quickly in the cache, you could localise this to the ST monad then, as its perfectly pure on the outside.
Ok, awesome! J:\dev\haskell>ghc -fglasgow-exts -O2 -o PrimeDonald2.exe PrimeDonald2.hs J:\dev\haskell>primedonald2 number of primes: 664579 Elapsed time: 0.7030000000000001 {-# OPTIONS -O2 -fbang-patterns #-} import Control.Monad.ST import Data.Array.ST import Data.Array.Base import System import Control.Monad import Data.Bits import System.Time import System.Locale pureSieve :: Int -> Int pureSieve n = runST( sieve n ) sieve n = do a <- newArray (2,n) True :: ST s (STUArray s Int Bool) -- an array of Bool go a n 2 0 go !a !m !n !c | n == m = return c | otherwise = do e <- unsafeRead a n if e then let loop !j | j < m = do x <- unsafeRead a j when x (unsafeWrite a j False) loop (j+n) | otherwise = go a m (n+1) (c+1) in loop (n `shiftL` 1) else go a m (n+1) c calculateNumberOfPrimes :: Int -> Int calculateNumberOfPrimes = pureSieve gettime :: IO ClockTime gettime = getClockTime main = do starttime <- gettime let numberOfPrimes = (calculateNumberOfPrimes 10000000) putStrLn( "number of primes: " ++ show( numberOfPrimes ) ) endtime <- gettime let timediff = diffClockTimes endtime starttime let secondsfloat = realToFrac( tdSec timediff ) + realToFrac(tdPicosec timediff) / 1000000000000 putStrLn( "Elapsed time: " ++ show(secondsfloat) ) return ()