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|
{-# LANGUAGE BangPatterns #-}
{-# LANGUAGE ScopedTypeVariables #-}
module ByteArray.Compare
( benchmark
, argumentSmall
, argumentMedium
, argumentLarge
) where
import Data.Primitive
import Data.Word
import Control.Monad
import Control.Monad.ST (runST)
import GHC.Exts (fromList)
-- This takes the cross product of the argument with itself
-- and compares each pair of combined ByteArrays. In other words,
-- it compare every ByteArray to every other ByteArray (including
-- itself). This is does efficiently and should not allocate
-- any memory.
benchmark :: Array ByteArray -> Int
benchmark !uarr = outer 0
where
sz = sizeofArray uarr
outer :: Int -> Int
outer !v0 =
let go !v !ix = if ix < sz
then go (inner v (indexArray uarr ix)) (ix + 1)
else v
in go v0 0
inner :: Int -> ByteArray -> Int
inner !v0 !barr =
let go !v !ix = if ix < sz
then
let !y = case compare barr (indexArray uarr ix) of
LT -> (-1)
EQ -> 0
GT -> 1
in go (v + y) (ix + 1)
else v
in go v0 0
-- This is an array of all byte arrays consistent of the bytes 0 and 1
-- bewteen length 0 and 7 inclusive:
--
-- []
-- [0]
-- [1]
-- [0,0]
-- [0,1]
-- ...
-- [1,1,1,1,1,1,0]
-- [1,1,1,1,1,1,1]
--
-- These are very small byte arrays. All of them are smaller than a
-- cache line. A comparison function that uses the FFI may perform
-- worse on such inputs than one that does not.
argumentSmall :: Array ByteArray
argumentSmall = runST $ do
let (ys :: [[Word8]]) = foldMap (\n -> replicateM n [0,1]) (enumFromTo 0 7)
marr <- newArray (length ys) undefined
let go !_ [] = return ()
go !ix (x : xs) = do
writeArray marr ix (fromList x)
go (ix + 1) xs
go 0 ys
unsafeFreezeArray marr
-- This is an array of all byte arrays consistent of the bytes 0 and 1
-- bewteen length 0 and 7 inclusive. However, they are all padded on the
-- left by the same 256 bytes. Comparing any two of them will require
-- walking and comparing the first 256 bytes.
argumentMedium :: Array ByteArray
argumentMedium = runST $ do
let (ys :: [[Word8]]) = foldMap (\n -> map (enumFromTo 0 255 ++) (replicateM n [0,1])) (enumFromTo 0 7)
marr <- newArray (length ys) undefined
let go !_ [] = return ()
go !ix (x : xs) = do
writeArray marr ix (fromList x)
go (ix + 1) xs
go 0 ys
unsafeFreezeArray marr
-- Same thing but with left padding of 1024 bytes.
argumentLarge :: Array ByteArray
argumentLarge = runST $ do
let (ys :: [[Word8]]) = foldMap (\n -> map (concat (replicate 4 (enumFromTo 0 255)) ++) (replicateM n [0,1])) (enumFromTo 0 7)
marr <- newArray (length ys) undefined
let go !_ [] = return ()
go !ix (x : xs) = do
writeArray marr ix (fromList x)
go (ix + 1) xs
go 0 ys
unsafeFreezeArray marr
|
