Shootout/Nsieve Bits

A ShootoutEntry for the nsieve-bits problem.

Each program should count the prime numbers from 2 to M, using the same na�ve Sieve of Eratosthenes algorithm:

• create an array of M bit flags
• for each index number
  • if the flag value at that index is true

j** set all the flag values at multiples of that index false

• • • increment the count

Calculate 3 prime counts, for M = 2N � 10000, 2N-1 � 10000, and 2N-2 � 10000.

Benchmarks

Linux/x86, N=10

|| Entry || Time || || Fast 3 || 0.656 || || Fast 2 || 0.720 || || Fast 1 || 1.028 || || Original|| 1.031 ||

(Proposed) Fast 3 entry

Careful attention to strictness ensures all args are unboxed (taking the idea from the NsieveEntry). Squeezes another 10%. This should be the 2nd or 3rd fastest entry overall -- finally beating OCaml, D and SML :)

--
-- The Great Computer Language Shootout
-- http://shootout.alioth.debian.org/
--
-- Haskell Shootout entries - http://haskell.org/hawiki/ShootoutEntry
-- Contributed by (c) Simon Marlow 2005
-- Modified by Don Stewart
--

import Data.Bits; import Data.Array.IO; import Data.Array.Base
import System; import IO; import Text.Printf

main = (\n -> mapM_ (sieve . shiftL 10000 . (-) n) [0..2]) . read . head =<< getArgs

sieve m = do r <- newArray (0,m) False >>= \(a::IOUArray Int Bool) -> for a m 2 0
             printf "Primes up to %8d %8d\n" (m::Int) (r::Int)

for arr m i c | arr `seq` m `seq` i `seq` c `seq` False = undefined -- strict
for arr m i c = if i > m then return c else do
    x <- unsafeRead arr i
    if x then for arr m (i+1) c
         else let for' j | j > m     = for arr m (i+1) (c+1)
                         | otherwise = unsafeWrite arr j True >> for' (j+i)
              in for' (i*2)

Fast 2 entry

Short, and uses unsafe reads for realistic speed Use -O2 -optc-O3.

--
-- The Great Computer Language Shootout
-- http://shootout.alioth.debian.org/
-- Contributed by (c) Simon Marlow 2005
-- Modified by Don Stewart
--

import Data.Bits; import Data.Array.IO; import Data.Array.Base
import System; import IO; import Text.Printf

main = (\n -> mapM_ (sieve.(10000 *).shiftL 1) [n,n-1,n-2]) . read . head =<< getArgs

sieve m = do
  arr <- newArray (0,m) False :: IO (IOUArray Int Bool)
  let for i c
        | c `seq` False = undefined -- strictness hack
        | otherwise = if i > m then return c else do
                x <- unsafeRead arr i
                if x then for (i+1) c
                     else let for' j | j > m = for (i+1) (c+1)
                                     | otherwise = unsafeWrite arr j True >> for' (j+i)
                          in for' (i*2)
  r <- for 2 0
  printf "Primes up to %8d %8d\n" (m::Int) (r::Int) :: IO ()

Fast 1 entry

Shorter, might be slightly faster too.

-- The Great Computer Language Shootout
-- http://shootout.alioth.debian.org/
-- Contributed by (c) Simon Marlow 2005
-- Modified by Don Stewart

import Data.Bits; import Data.Array.IO; import System; import IO; import Text.Printf

main = (\n -> mapM_ (sieve.(10000 *).shiftL 1) [n,n-1,n-2]) . read . head =<< getArgs

sieve m = do
  arr <- newArray (0,m) False :: IO (IOUArray Int Bool)
  let for i c
        | c `seq` False = undefined -- strictness hack
        | otherwise = if i > m then return c else do
                x <- readArray arr i
                if x then for (i+1) c
                     else let for' j | j > m = for (i+1) (c+1)
                                     | otherwise = writeArray arr j True >> for' (j+i)
                          in for' (i*2)
  r <- for 2 0
  printf "Primes up to %8d %8d\n" (m::Int) (r::Int) :: IO ()

Original entry

{-# OPTIONS -O2 -optc-O3 #-}
-- The Great Computer Language Shootout
-- http://shootout.alioth.debian.org/
-- Contributed by (c) Simon Marlow 2005

import Data.Array.IO
import System
import IO
import Monad
import Data.Bits
import Text.Printf

main = do
  as <- getArgs
  case as of
    [m] -> do let n = read m :: Int
              test n
              when (n >= 1) $ test (n-1)
              when (n >= 2) $ test (n-2)
    _   -> do hPutStrLn stderr "usage: nsieve-bits M"
              exitWith (ExitFailure 1)

test :: Int -> IO ()
test n = do
  let m = (1 `shiftL` n) * 10000
  arr <- newArray (0,m) False :: IO (IOUArray Int Bool)
  let for i count
        | count `seq` False = undefined -- strictness hack
        | i > m = return count
        | otherwise = do
                x <- readArray arr i
                if x
                  then for (i+1) count
                  else let for' j | j > m = for (i+1) (count+1)
                                  | otherwise = do
                                        writeArray arr j True
                                        for' (j + i)
                       in for' (i*2)
  r <- for 2 0
  printf "Primes up to %8d %8d\n" (m::Int) (r::Int)