memchr vs strchr

README.md

To compile and run:

# Get Haskell/Cabal
cabal update && cabal install criterion
gcc -c -O3 Lib.c
ghc Main.hs Lib.o
./Main

Lib.c

#include <stddef.h>

// From http://clc-wiki.net/wiki/strchr
char *strchr_c(const char *s, int c)
{
    while (*s != (char)c)
        if (!*s++)
            return 0;
    return (char *)s;
}

// From http://clc-wiki.net/wiki/memchr
void *memchr_c(const void *s, int c, size_t n)
{
    unsigned char *p = (unsigned char*)s;
    while( n-- )
        if( *p != (unsigned char)c )
            p++;
        else
            return p;
    return 0;
}

Main.hs

import qualified Data.ByteString as BS
import qualified Data.ByteString.Unsafe as BS
import Criterion.Main
import Foreign
import Foreign.C.Types
import System.IO.Unsafe
import Data.Monoid

foreign import ccall unsafe "string.h memchr" memchr_std :: Ptr Word8 -> CInt -> CSize -> IO (Ptr Word8)
foreign import ccall unsafe "string.h strchr" strchr_std :: Ptr Word8 -> CInt -> IO (Ptr Word8)
foreign import ccall unsafe memchr_c :: Ptr Word8 -> CInt -> CSize -> IO (Ptr Word8)
foreign import ccall unsafe strchr_c :: Ptr Word8 -> CInt -> IO (Ptr Word8)

ignoreSize f a b _ = f a b

cstr i = BS.replicate i 32 <> BS.singleton 64 <> BS.replicate i 32 <> BS.singleton 0

funs =
    [("memchr_std", memchr_std)
    ,("strchr_std", ignoreSize strchr_std)
    ,("memchr_c", memchr_c)
    ,("strchr_c", ignoreSize strchr_c)]

main = defaultMain
    [ seq bs $ bench (show i ++ " " ++ name) $ whnfIO $ test fun bs
    | i <- [1,10,100,1000,10000,100000,1000000,10000000]
    , let bs = cstr i
    , (name, fun) <- funs]

{-# NOINLINE test #-}
test fun bs =
    BS.unsafeUseAsCStringLen bs $ \(ptr,len) ->
        fun (castPtr ptr) 64 (fromIntegral len)