On Wednesday 20 April 2011 21:55:51, Dan Doel wrote:
>
> It's not a statistics bug. I'm reproducing it here using just
> vector-algorithms.
Yep. Attached a simple testcasewhich reproduces it and uses only vector and
vector-algorithms.
>
> Fill a vector of size N with [N..1], and (intro) sort it, and you get
> NaNs. But only with -O or above.
However, for me the NaNs disappear with the -msse2 option.
> Without optimization it doesn't
> happen (and nothing seems to be reading/writing out of bounds, as I
> compiled vector with UnsafeChecks earlier and it didn't complain).
Nor does it happen here with 7.0.2 or 7.0.1.
>
> Filling the vector with [1..N] also doesn't trigger the NaNs. [0,0..0]
> and [0,0..1] trigger it.
>
> I don't know what's going on yet. I have trouble believing it's a bug
> in vector-algorithms code, though, as I don't think I've written any
> RULEs (just INLINEs), and that's the one thing that comes to mind in
> library code that could cause a difference between -O0 and -O. So I'd
> tentatively suggest it's a vector, base or compiler bug.
>
> The above testing is on 64-bit windows running a 32-bit copy of GHC,
> for reference.
32-bit linux here
>
> My ability to investigate this will be a bit limited for the near
> future. If someone definitively tracks it down to bugs in my code,
> though, let me know, and I'll try and push a new release up on
> hackage.
>
> -- Dan
{-# LANGUAGE BangPatterns #-}
module Main where
import qualified Data.Vector.Unboxed.Mutable as MU
import Data.Vector.Unboxed.Mutable (IOVector, unsafeRead, unsafeWrite, new)
import qualified Data.Vector.Algorithms.Intro as I
import Control.Monad (when)
import System.Environment (getArgs)
countNaNs :: IOVector Double -> IO Int
countNaNs a = go 0 0
where
len = MU.length a
go !ct i
| i < len = do
x <- unsafeRead a i
go (if isNaN x then ct+1 else ct) (i+1)
| otherwise = return ct
sample :: Int -> IO (IOVector Double)
sample k = do
a <- new k
let foo :: Double -> Double
foo x = 1.0 + sin x / x
fill i x
| i < k = do
unsafeWrite a i (foo x)
fill (i+1) (x+1.0)
| otherwise = return a
fill 0 (fromIntegral k * 10)
main :: IO ()
main = do
args <- getArgs
let k = case args of
(arg:_) -> read arg
_ -> 10000
a <- sample k
b <- countNaNs a
when (b /= 0) (putStrLn $ "Before sorting: " ++ show b ++ " NaNs.")
I.sort a
c <- countNaNs a
when (c /= 0) (putStrLn $ "After sorting: " ++ show c ++ " NaNs.")
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