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Evaluate "(MOSTNEG INT) \ -1" correctly when evaluating constants.

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This actually crashes older versions of GHC:
  Prelude Data.Int> (minBound :: Int32) `div` (-1)
  Floating point exception
This commit is contained in:
Adam Sampson 2008-03-19 11:12:57 +00:00
parent b1416bb0cf
commit 7f6cb6e0c3
1 changed files with 14 additions and 2 deletions
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16
common/EvalConstants.hs
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@ -219,13 +219,25 @@ logicalShiftR :: Bits a => a -> Int -> a
logicalShiftR val 0 = val
logicalShiftR val n = rotateR (foldl clearBit val [0 .. (n - 1)]) n
-- | Equivalent to 'div', but handles @minBound `div` (-1)@ correctly.
-- (GHC's doesn't, at least as of 6.8.1.)
safeDiv :: Integral a => a -> a -> a
safeDiv a (-1) = 0
safeDiv a b = div a b
-- | Equivalent to 'rem', but handles @minBound `rem` (-1)@ correctly.
-- (GHC's doesn't, at least as of 6.8.1.)
safeRem :: Integral a => a -> a -> a
safeRem a (-1) = 0
safeRem a b = rem a b
evalDyadic :: A.DyadicOp -> OccValue -> OccValue -> EvalM OccValue
-- FIXME These should check for overflow.
evalDyadic A.Add a b = evalDyadicOp (+) a b
evalDyadic A.Subtr a b = evalDyadicOp (-) a b
evalDyadic A.Mul a b = evalDyadicOp (*) a b
evalDyadic A.Div a b = evalDyadicOp div a b
evalDyadic A.Rem a b = evalDyadicOp rem a b
evalDyadic A.Div a b = evalDyadicOp safeDiv a b
evalDyadic A.Rem a b = evalDyadicOp safeRem a b
-- ... end FIXME
evalDyadic A.Plus a b = evalDyadicOp (+) a b
evalDyadic A.Minus a b = evalDyadicOp (-) a b