Bit parsing speed

gistfile1.hs

module Main where

import Control.Applicative
import System.Environment
import Control.Monad
import qualified Data.ByteString.Lazy as BSL

import Data.Bits
import Data.Binary.Get
import Data.Binary.Bits.Get as Bits

import Criterion.Main

data Cnt = Cnt !Int deriving Show

readBitByBit content =
  let l = BSL.length content
      res = runGet (runBitGet (getAllBits (l*8))) content
      in res
  where
    getAllBits 0 = return $ Cnt 0
    getAllBits n = do
      b <- getBool
      let c = if b then 1 else 0
      Cnt rest <- getAllBits (n-1)
      return $ Cnt $ c+rest


readByteByByte content =
  let l = BSL.length content
      res = runGet (runBitGet (getAllBits l)) content
      in res
  where
    getAllBits 0 = return $ Cnt 0
    getAllBits n = do
      b <- Bits.getWord8 8
      let c = sum [1 |n<-[0..7], testBit b n]
      Cnt rest <- getAllBits (n-1)
      return $ Cnt $ c+rest

read8BitsAtOnce content = do
  let l = BSL.length content
  let res = runGet (runBitGet (getAllBits l)) content
  return res
  where
    getAllBits 0 = return $ Cnt 0
    getAllBits n = do
      let blk = count <$> bool <*> bool <*> bool <*> bool <*> bool <*> bool <*> bool <*> bool
      c <- block blk
      Cnt rest <- getAllBits (n-1)
      return $ Cnt $ c+rest
    count a b c d e f g h = length $ filter (==True) [a,b,c,d,e,f,g,h]

main = do
  let fname = "stockdb.hi" -- approx 32K
  raw <- BSL.readFile fname
  defaultMain [ bench "1 bit at a time"            $ whnf readBitByBit raw
              , bench "1 byte at a time + testBit" $ whnf readByteByByte raw
              , bench "8 bits at a time" $ whnfIO (read8BitsAtOnce raw)
              ]

{-
warming up
estimating clock resolution...
mean is 8.378154 us (80001 iterations)
found 2250 outliers among 79999 samples (2.8%)
  1172 (1.5%) high mild
  1078 (1.3%) high severe
estimating cost of a clock call...
mean is 544.7900 ns (77 iterations)
found 10 outliers among 77 samples (13.0%)
  2 (2.6%) high mild
  8 (10.4%) high severe

benchmarking 1 bit at a time
collecting 100 samples, 1 iterations each, in estimated 88.67671 s
mean: 834.7386 ms, lb 833.0525 ms, ub 837.1857 ms, ci 0.950
std dev: 10.30825 ms, lb 7.862752 ms, ub 16.31547 ms, ci 0.950

benchmarking 1 byte at a time + testBit
collecting 100 samples, 1 iterations each, in estimated 5.750108 s
mean: 56.64881 ms, lb 56.38399 ms, ub 56.94305 ms, ci 0.950
std dev: 1.424958 ms, lb 1.187093 ms, ub 1.964934 ms, ci 0.950
found 2 outliers among 100 samples (2.0%)
  1 (1.0%) high severe
variance introduced by outliers: 19.012%
variance is moderately inflated by outliers

benchmarking 8 bits at a time
collecting 100 samples, 1 iterations each, in estimated 7.785916 s
mean: 75.72581 ms, lb 75.44328 ms, ub 76.02788 ms, ci 0.950
std dev: 1.505365 ms, lb 1.364304 ms, ub 1.734008 ms, ci 0.950
variance introduced by outliers: 13.225%
variance is moderately inflated by outliers
-}