#2647: Serious typo in IntMap.hs
----------------------------------+-----------------------------------------
Reporter: sedillard | Owner:
Type: bug | Status: new
Priority: normal | Component: libraries (other)
Version: 6.8.3 | Severity: critical
Keywords: containers IntMap | Testcase:
Architecture: Unknown/Multiple | Os: Unknown/Multiple
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Someone has recently (since 6.8.3) taken a "style" pass over `IntMap.hs`.
Apparently they didn't like reusing identifiers in different scopes, so
they changed this function (at the very core of `IntMap`) from this
{{{
highestBitMask :: Nat -> Nat
highestBitMask x
= case (x .|. shiftRL x 1) of
x -> case (x .|. shiftRL x 2) of
x -> case (x .|. shiftRL x 4) of
x -> case (x .|. shiftRL x 8) of
x -> case (x .|. shiftRL x 16) of
x -> case (x .|. shiftRL x 32) of -- for 64 bit platforms
x -> (x `xor` (shiftRL x 1))
}}}
to this
{{{
highestBitMask :: Nat -> Nat
highestBitMask x0
= case (x0 .|. shiftRL x0 1) of
x1 -> case (x1 .|. shiftRL x1 2) of
x2 -> case (x2 .|. shiftRL x2 4) of
x3 -> case (x3 .|. shiftRL x3 8) of
x4 -> case (x3 .|. shiftRL x4 16) of
x5 -> case (x4 .|. shiftRL x5 32) of -- for 64 bit platforms
x6 -> (x6 `xor` (shiftRL x6 1))
}}}
If you stare at it long enough, you might find the typo. Don't cheat and
look at the patch. I'll give you a hint: quickcheck won't find it because
the tests don't use big enough integers.
Needless to say this completely breaks the library, and if it ain't
broke... :)
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2647>
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