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Corrected checkConstantEq to actually remove the constant equations, rather than only checking them for consistency

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This commit is contained in:
Neil Brown 2007-12-14 16:45:34 +00:00
parent d9b606143e
commit 9d562c0b12
1 changed files with 13 additions and 5 deletions
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18
transformations/ArrayUsageCheck.hs
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@ -216,11 +216,12 @@ mygcdList (x:xs) = foldl mygcd x xs
-- and turns any 2x + y <= 4, 2x + y >= 4 pairs into equalities. The list of such equalities
-- (which may well be an empty list) and the remaining inequalities is returned.
-- As an additional step not specified in the paper, equations with no variables in them are checked
-- for consistency. That is, all equations c >= 0 (where c is constant) are checked to ensure c is indeed >= 0.
-- for consistency. That is, all equations c >= 0 (where c is constant) are checked to
-- ensure c is indeed >= 0, and those equations are removed.
pruneAndCheck :: InequalityProblem -> Maybe (EqualityProblem, InequalityProblem)
pruneAndCheck ineq = do let (opps,others) = splitEither $ groupOpposites $ map pruneGroup groupedIneq
(opps', eq) <- mapM checkOpposite opps >>* splitEither
checked <- mapM checkConstantEq (concat opps' ++ others)
checked <- mapM checkConstantEq (concat opps' ++ others) >>* catMaybes
return (eq, checked)
where
groupedIneq = groupBy (\x y -> EQ == coeffSort x y) $ sortBy coeffSort ineq
@ -283,9 +284,16 @@ pruneAndCheck ineq = do let (opps,others) = splitEither $ groupOpposites $ map p
| (x ! 0) + (y ! 0) == 0 = Just $ Right x
| otherwise = Just $ Left [x,y]
checkConstantEq :: InequalityConstraintEquation -> Maybe InequalityConstraintEquation
checkConstantEq eq | all (== 0) (tail $ elems eq) = if (eq ! 0) >= 0 then Just eq else Nothing
| otherwise = Just eq
-- The type of this function is quite confusing. We want to use in the Maybe monad, so
-- the outer type indicates error; Nothing is an error. Just x indicates non-failure,
-- but x may either be Just y (keep the equation) or Nothing (remove it). So the three
-- possible returns are:
-- * Nothing: Equation inconsistent
-- * Just Nothing: Equation redundant
-- * Just (Just e) : Keep equation.
checkConstantEq :: InequalityConstraintEquation -> Maybe (Maybe InequalityConstraintEquation)
checkConstantEq eq | all (== 0) (tail $ elems eq) = if (eq ! 0) >= 0 then Just Nothing else Nothing
| otherwise = Just $ Just eq
-- | Returns Nothing if there is definitely no solution, or (Just ineq) if
-- further investigation is needed