On Saturday 03 February 2007 19:42, kahl@cas.mcmaster.ca wrote:
I have re-written SHA1 so that is more idiomatically haskell and it is easy to see how it implements the specification. The only problem is I now have a space leak. I can see where the leak is but I'm less sure what to do about getting rid of it.
Here's the offending function:
pad :: [Word8] -> [Word8] pad xs = xs ++ [0x80] ++ ps ++ lb where l = length xs pl = (64-(l+9)) `mod` 64 ps = replicate pl 0x00 lb = i2osp 8 (8*l)
I would try something along the following lines (untested):
\begin{spec} catWithLen xs f = xs ++ f (length xs) \end{spec}
\begin{code} catWithLen :: [a] -> (Int -> [a]) -> [a] catWithLen xs f = h 0 xs where h k [] = f k h k (x : xs) = case succ k of -- forcing evaluation k' -> x : h k' xs \end{code}
\begin{code} pad :: [Word8] -> [Word8] pad xs = catWithLen xs f where f l = 0x80 : ps lb where -- we know that |l = length xs| pl = (64-(l+9)) `mod` 64 ps = funPow pl (0x00 :) lb = i2osp 8 (8*l) \end{code}
If you are lucky, then the replicate and the (++lb) in the original code might be fused by the compiler as an instance of foldr-build or something related --- check the optimised core code.
Wolfram, Thanks but this gives a different problem: dom@heisenberg:~/sha1> ./allInOne 1000001 +RTS -hc -RTS [2845392438,1191608682,3124634993,2018558572,2630932637] [2224569924,473682542,3131984545,4182845925,3846598897] Stack space overflow: current size 8388608 bytes. Use `+RTS -Ksize' to increase it. Dominic.