diff options
| -rw-r--r-- | libraries/base/GHC/Real.hs | 19 |
1 files changed, 11 insertions, 8 deletions
diff --git a/libraries/base/GHC/Real.hs b/libraries/base/GHC/Real.hs index 38a3aa2870..1425f8c306 100644 --- a/libraries/base/GHC/Real.hs +++ b/libraries/base/GHC/Real.hs @@ -334,11 +334,8 @@ instance Integral Int where -- in GHC.Int | otherwise = a `quotInt` b - a `rem` b + !a `rem` b -- See Note [Special case of mod and rem is lazy] | b == 0 = divZeroError - -- The quotRem CPU instruction fails for minBound `quotRem` -1, - -- but minBound `rem` -1 is well-defined (0). We therefore - -- special-case it. | b == (-1) = 0 | otherwise = a `remInt` b @@ -348,11 +345,8 @@ instance Integral Int where -- in GHC.Int | otherwise = a `divInt` b - a `mod` b + !a `mod` b -- See Note [Special case of mod and rem is lazy] | b == 0 = divZeroError - -- The divMod CPU instruction fails for minBound `divMod` -1, - -- but minBound `mod` -1 is well-defined (0). We therefore - -- special-case it. | b == (-1) = 0 | otherwise = a `modInt` b @@ -368,6 +362,15 @@ instance Integral Int where | b == (-1) && a == minBound = (overflowError, 0) | otherwise = a `divModInt` b +{- Note [Special case of mod and rem is lazy] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +The `quotRem`/`divMod` CPU instruction fails for minBound `quotRem` -1, but +minBound `rem` -1 is well-defined (0). We therefore special-case for `b == -1`, +but not for `a == minBound` because of Note [Order of tests] in GHC.Int. But +now we have to make sure the function stays strict in a, to guarantee unboxing. +Hence the bang on a, see #18187. +-} + -------------------------------------------------------------- -- Instances for @Word@ -------------------------------------------------------------- |