有效地将一个字节串转换为十六进制表示

Question

我需要能够给出SHA512散列的十六进制表示。也许我只是不够努力，但我可以在Hackage上找到任何功能来完成它。所以我写了一个使用unfoldrN的实现。这对我的目的来说绝对足够快，但我想知道是否有人知道更快的方法。

我把我的实现放在Github上作为一个要点：https://gist.github.com/2356925。该文件还包含基于Numeric.showHex的简单实现，QuickCheck测试和标准基准。我目前的简单版本兑unfoldrN版本的结果是：

benchmarking simple 
mean: 4.677296 ms, lb 4.656011 ms, ub 4.696684 ms, ci 0.950 
std dev: 104.2791 us, lb 87.77023 us, ub 128.1627 us, ci 0.950 
found 5 outliers among 100 samples (5.0%) 
    4 (4.0%) low mild 
variance introduced by outliers: 15.195% 
variance is moderately inflated by outliers 

benchmarking unfoldrN_MS1 
mean: 370.0101 us, lb 365.9819 us, ub 373.8619 us, ci 0.950 
std dev: 20.17016 us, lb 16.92772 us, ub 24.08982 us, ci 0.950 
found 14 outliers among 100 samples (14.0%) 
    7 (7.0%) low mild 
    7 (7.0%) high mild 
variance introduced by outliers: 52.467% 
variance is severely inflated by outliers 

任何人想借此刺改善呢？

Answer 1

走出低层次，

import Data.ByteString.Internal 
import Foreign.Ptr 
import Foreign.Storable 
import qualified Data.ByteString as B 
import Data.ByteString.Unsafe 
import Data.Bits 
import Data.Word 

maxLen :: Int 
maxLen = maxBound `quot` 2 

hexDig :: Word8 -> Word8 
hexDig d 
    | d < 10 = d + 48 
    | otherwise = d + 87 

toHex :: ByteString -> ByteString 
toHex bs 
    | len > maxLen = error "too long to convert" 
    | otherwise = unsafeCreate nl (go 0) 
     where 
     len = B.length bs 
     nl = 2*len 
     go i p 
      | i == len = return() 
      | otherwise = case unsafeIndex bs i of 
          w -> do poke p (hexDig $ w `shiftR` 4) 
            poke (p `plusPtr` 1) (hexDig $ w .&. 0xF) 
            go (i+1) (p `plusPtr` 2) 

我可以约3.5的另一个因素减少对我的盒子的转换时间。制作sample的时间长一点（25000），我得到了

benchmarking simple 
mean: 13.76532 ms, lb 13.64184 ms, ub 13.88680 ms, ci 0.950 
std dev: 633.2413 us, lb 582.6342 us, ub 687.9701 us, ci 0.950 
variance introduced by outliers: 44.438% 
variance is moderately inflated by outliers 

benchmarking unfoldrN_MS1 
mean: 430.5705 us, lb 424.9206 us, ub 438.5689 us, ci 0.950 
std dev: 33.85429 us, lb 26.25623 us, ub 45.74915 us, ci 0.950 
found 4 outliers among 100 samples (4.0%) 
    3 (3.0%) high mild 
    1 (1.0%) high severe 
variance introduced by outliers: 69.726% 
variance is severely inflated by outliers 

benchmarking LowHex 
mean: 123.6000 us, lb 123.0551 us, ub 124.7084 us, ci 0.950 
std dev: 3.837497 us, lb 1.869370 us, ub 6.470112 us, ci 0.950 
found 6 outliers among 100 samples (6.0%) 
    4 (4.0%) high mild 
    2 (2.0%) high severe 
variance introduced by outliers: 25.818% 
variance is moderately inflated by outliers 

对于原来的500长sample，这是

benchmarking simple 
mean: 2.603306 ms, lb 2.583054 ms, ub 2.629212 ms, ci 0.950 
std dev: 116.5341 us, lb 81.61409 us, ub 191.3293 us, ci 0.950 
found 7 outliers among 100 samples (7.0%) 
    2 (2.0%) low severe 
    3 (3.0%) low mild 
    1 (1.0%) high severe 
variance introduced by outliers: 42.490% 
variance is moderately inflated by outliers 

benchmarking unfoldrN_MS1 
mean: 83.19349 us, lb 82.88474 us, ub 83.58283 us, ci 0.950 
std dev: 1.771460 us, lb 1.486104 us, ub 2.174729 us, ci 0.950 
found 14 outliers among 100 samples (14.0%) 
    12 (12.0%) high mild 
    2 (2.0%) high severe 
variance introduced by outliers: 14.225% 
variance is moderately inflated by outliers 

benchmarking LowHex 
mean: 24.50564 us, lb 24.41683 us, ub 24.61241 us, ci 0.950 
std dev: 497.1908 ns, lb 415.6366 ns, ub 609.7594 ns, ci 0.950 
found 5 outliers among 100 samples (5.0%) 
    5 (5.0%) high mild 
variance introduced by outliers: 13.256% 
variance is moderately inflated by outliers 

Answer 2

它看起来像我刚才用

hex :: B.ByteString -> String 
hex = concatMap (printf "%02x") . B.unpack 

我最后一次想要这样做。这与Crypto.Hash库iirc一起使用。我怀疑它的性能如此之好，但与（慢）sha512函数本身相比，为什么十六进制转换会成为一个问题？

Answer 3

您正在寻找的函数是Data.ByteString.Builder.byteStringHex（或其Lazy ByteStrings的双函数），它由新的字节串构建器提供。我extended your benchmarks并得到我的机器上，结果如下：

benchmarking size 5000/simple 
mean: 2.469847 ms, lb 2.440422 ms, ub 2.522850 ms, ci 0.950 
std dev: 196.5903 us, lb 116.8811 us, ub 318.4720 us, ci 0.950 
found 16 outliers among 100 samples (16.0%) 
    3 (3.0%) low severe 
    2 (2.0%) low mild 
    10 (10.0%) high severe 
variance introduced by outliers: 70.721% 
variance is severely inflated by outliers 

benchmarking size 5000/unfoldrN_MS1 
mean: 102.6075 us, lb 101.7695 us, ub 104.0159 us, ci 0.950 
std dev: 5.468574 us, lb 3.681120 us, ub 8.080665 us, ci 0.950 
found 16 outliers among 100 samples (16.0%) 
    6 (6.0%) high mild 
    10 (10.0%) high severe 
variance introduced by outliers: 51.455% 
variance is severely inflated by outliers 

benchmarking size 5000/byteStringHexFixed 
mean: 5.675204 us, lb 5.636296 us, ub 5.750211 us, ci 0.950 
std dev: 264.3726 ns, lb 140.9738 ns, ub 398.8494 ns, ci 0.950 
found 5 outliers among 100 samples (5.0%) 
    4 (4.0%) high severe 
variance introduced by outliers: 44.476% 
variance is moderately inflated by outliers 

我喜欢这个号码。太糟糕了，我的字节串库的补丁仍在Duncan Coutts的审查之中。最迟，新的字符串构建器将在下一个GHC版本中提供。