instance Integral Int8 where
quot x@(I8# x#) y@(I8# y#)
| y == 0 = divZeroError
- | y == (-1) && x == minBound = overflowError
+ | y == (-1) && x == minBound = overflowError -- Note [Order of tests]
| otherwise = I8# (narrow8Int# (x# `quotInt#` y#))
rem x@(I8# x#) y@(I8# y#)
| y == 0 = divZeroError
- | y == (-1) && x == minBound = overflowError
+ | y == (-1) && x == minBound = overflowError -- Note [Order of tests]
| otherwise = I8# (narrow8Int# (x# `remInt#` y#))
div x@(I8# x#) y@(I8# y#)
| y == 0 = divZeroError
- | y == (-1) && x == minBound = overflowError
+ | y == (-1) && x == minBound = overflowError -- Note [Order of tests]
| otherwise = I8# (narrow8Int# (x# `divInt#` y#))
mod x@(I8# x#) y@(I8# y#)
| y == 0 = divZeroError
- | y == (-1) && x == minBound = overflowError
+ | y == (-1) && x == minBound = overflowError -- Note [Order of tests]
| otherwise = I8# (narrow8Int# (x# `modInt#` y#))
quotRem x@(I8# x#) y@(I8# y#)
| y == 0 = divZeroError
- | y == (-1) && x == minBound = overflowError
+ | y == (-1) && x == minBound = overflowError -- Note [Order of tests]
| otherwise = (I8# (narrow8Int# (x# `quotInt#` y#)),
I8# (narrow8Int# (x# `remInt#` y#)))
divMod x@(I8# x#) y@(I8# y#)
| y == 0 = divZeroError
- | y == (-1) && x == minBound = overflowError
+ | y == (-1) && x == minBound = overflowError -- Note [Order of tests]
| otherwise = (I8# (narrow8Int# (x# `divInt#` y#)),
I8# (narrow8Int# (x# `modInt#` y#)))
toInteger (I8# x#) = smallInteger x#
instance Integral Int16 where
quot x@(I16# x#) y@(I16# y#)
| y == 0 = divZeroError
- | y == (-1) && x == minBound = overflowError
+ | y == (-1) && x == minBound = overflowError -- Note [Order of tests]
| otherwise = I16# (narrow16Int# (x# `quotInt#` y#))
rem x@(I16# x#) y@(I16# y#)
| y == 0 = divZeroError
- | y == (-1) && x == minBound = overflowError
+ | y == (-1) && x == minBound = overflowError -- Note [Order of tests]
| otherwise = I16# (narrow16Int# (x# `remInt#` y#))
div x@(I16# x#) y@(I16# y#)
| y == 0 = divZeroError
- | y == (-1) && x == minBound = overflowError
+ | y == (-1) && x == minBound = overflowError -- Note [Order of tests]
| otherwise = I16# (narrow16Int# (x# `divInt#` y#))
mod x@(I16# x#) y@(I16# y#)
| y == 0 = divZeroError
- | y == (-1) && x == minBound = overflowError
+ | y == (-1) && x == minBound = overflowError -- Note [Order of tests]
| otherwise = I16# (narrow16Int# (x# `modInt#` y#))
quotRem x@(I16# x#) y@(I16# y#)
| y == 0 = divZeroError
- | y == (-1) && x == minBound = overflowError
+ | y == (-1) && x == minBound = overflowError -- Note [Order of tests]
| otherwise = (I16# (narrow16Int# (x# `quotInt#` y#)),
I16# (narrow16Int# (x# `remInt#` y#)))
divMod x@(I16# x#) y@(I16# y#)
| y == 0 = divZeroError
- | y == (-1) && x == minBound = overflowError
+ | y == (-1) && x == minBound = overflowError -- Note [Order of tests]
| otherwise = (I16# (narrow16Int# (x# `divInt#` y#)),
I16# (narrow16Int# (x# `modInt#` y#)))
toInteger (I16# x#) = smallInteger x#
instance Integral Int32 where
quot x@(I32# x#) y@(I32# y#)
| y == 0 = divZeroError
- | y == (-1) && x == minBound = overflowError
+ | y == (-1) && x == minBound = overflowError -- Note [Order of tests]
| otherwise = I32# (x# `quotInt32#` y#)
rem x@(I32# x#) y@(I32# y#)
| y == 0 = divZeroError
- | y == (-1) && x == minBound = overflowError
+ | y == (-1) && x == minBound = overflowError -- Note [Order of tests]
| otherwise = I32# (x# `remInt32#` y#)
div x@(I32# x#) y@(I32# y#)
| y == 0 = divZeroError
- | y == (-1) && x == minBound = overflowError
+ | y == (-1) && x == minBound = overflowError -- Note [Order of tests]
| otherwise = I32# (x# `divInt32#` y#)
mod x@(I32# x#) y@(I32# y#)
| y == 0 = divZeroError
- | y == (-1) && x == minBound = overflowError
+ | y == (-1) && x == minBound = overflowError -- Note [Order of tests]
| otherwise = I32# (x# `modInt32#` y#)
quotRem x@(I32# x#) y@(I32# y#)
| y == 0 = divZeroError
- | y == (-1) && x == minBound = overflowError
+ | y == (-1) && x == minBound = overflowError -- Note [Order of tests]
| otherwise = (I32# (x# `quotInt32#` y#),
I32# (x# `remInt32#` y#))
divMod x@(I32# x#) y@(I32# y#)
| y == 0 = divZeroError
- | y == (-1) && x == minBound = overflowError
+ | y == (-1) && x == minBound = overflowError -- Note [Order of tests]
| otherwise = (I32# (x# `divInt32#` y#),
I32# (x# `modInt32#` y#))
toInteger x@(I32# x#)
instance Integral Int32 where
quot x@(I32# x#) y@(I32# y#)
| y == 0 = divZeroError
- | y == (-1) && x == minBound = overflowError
+ | y == (-1) && x == minBound = overflowError -- Note [Order of tests]
| otherwise = I32# (narrow32Int# (x# `quotInt#` y#))
rem x@(I32# x#) y@(I32# y#)
| y == 0 = divZeroError
- | y == (-1) && x == minBound = overflowError
+ | y == (-1) && x == minBound = overflowError -- Note [Order of tests]
| otherwise = I32# (narrow32Int# (x# `remInt#` y#))
div x@(I32# x#) y@(I32# y#)
| y == 0 = divZeroError
- | y == (-1) && x == minBound = overflowError
+ | y == (-1) && x == minBound = overflowError -- Note [Order of tests]
| otherwise = I32# (narrow32Int# (x# `divInt#` y#))
mod x@(I32# x#) y@(I32# y#)
| y == 0 = divZeroError
- | y == (-1) && x == minBound = overflowError
+ | y == (-1) && x == minBound = overflowError -- Note [Order of tests]
| otherwise = I32# (narrow32Int# (x# `modInt#` y#))
quotRem x@(I32# x#) y@(I32# y#)
| y == 0 = divZeroError
- | y == (-1) && x == minBound = overflowError
+ | y == (-1) && x == minBound = overflowError -- Note [Order of tests]
| otherwise = (I32# (narrow32Int# (x# `quotInt#` y#)),
I32# (narrow32Int# (x# `remInt#` y#)))
divMod x@(I32# x#) y@(I32# y#)
| y == 0 = divZeroError
- | y == (-1) && x == minBound = overflowError
+ | y == (-1) && x == minBound = overflowError -- Note [Order of tests]
| otherwise = (I32# (narrow32Int# (x# `divInt#` y#)),
I32# (narrow32Int# (x# `modInt#` y#)))
toInteger (I32# x#) = smallInteger x#
instance Integral Int64 where
quot x@(I64# x#) y@(I64# y#)
| y == 0 = divZeroError
- | y == (-1) && x == minBound = overflowError
+ | y == (-1) && x == minBound = overflowError -- Note [Order of tests]
| otherwise = I64# (x# `quotInt64#` y#)
rem x@(I64# x#) y@(I64# y#)
| y == 0 = divZeroError
- | y == (-1) && x == minBound = overflowError
+ | y == (-1) && x == minBound = overflowError -- Note [Order of tests]
| otherwise = I64# (x# `remInt64#` y#)
div x@(I64# x#) y@(I64# y#)
| y == 0 = divZeroError
- | y == (-1) && x == minBound = overflowError
+ | y == (-1) && x == minBound = overflowError -- Note [Order of tests]
| otherwise = I64# (x# `divInt64#` y#)
mod x@(I64# x#) y@(I64# y#)
| y == 0 = divZeroError
- | y == (-1) && x == minBound = overflowError
+ | y == (-1) && x == minBound = overflowError -- Note [Order of tests]
| otherwise = I64# (x# `modInt64#` y#)
quotRem x@(I64# x#) y@(I64# y#)
| y == 0 = divZeroError
- | y == (-1) && x == minBound = overflowError
+ | y == (-1) && x == minBound = overflowError -- Note [Order of tests]
| otherwise = (I64# (x# `quotInt64#` y#),
I64# (x# `remInt64#` y#))
divMod x@(I64# x#) y@(I64# y#)
| y == 0 = divZeroError
- | y == (-1) && x == minBound = overflowError
+ | y == (-1) && x == minBound = overflowError -- Note [Order of tests]
| otherwise = (I64# (x# `divInt64#` y#),
I64# (x# `modInt64#` y#))
toInteger (I64# x) = int64ToInteger x
instance Integral Int64 where
quot x@(I64# x#) y@(I64# y#)
| y == 0 = divZeroError
- | y == (-1) && x == minBound = overflowError
+ | y == (-1) && x == minBound = overflowError -- Note [Order of tests]
| otherwise = I64# (x# `quotInt#` y#)
rem x@(I64# x#) y@(I64# y#)
| y == 0 = divZeroError
- | y == (-1) && x == minBound = overflowError
+ | y == (-1) && x == minBound = overflowError -- Note [Order of tests]
| otherwise = I64# (x# `remInt#` y#)
div x@(I64# x#) y@(I64# y#)
| y == 0 = divZeroError
- | y == (-1) && x == minBound = overflowError
+ | y == (-1) && x == minBound = overflowError -- Note [Order of tests]
| otherwise = I64# (x# `divInt#` y#)
mod x@(I64# x#) y@(I64# y#)
| y == 0 = divZeroError
- | y == (-1) && x == minBound = overflowError
+ | y == (-1) && x == minBound = overflowError -- Note [Order of tests]
| otherwise = I64# (x# `modInt#` y#)
quotRem x@(I64# x#) y@(I64# y#)
| y == 0 = divZeroError
- | y == (-1) && x == minBound = overflowError
+ | y == (-1) && x == minBound = overflowError -- Note [Order of tests]
| otherwise = (I64# (x# `quotInt#` y#), I64# (x# `remInt#` y#))
divMod x@(I64# x#) y@(I64# y#)
| y == 0 = divZeroError
- | y == (-1) && x == minBound = overflowError
+ | y == (-1) && x == minBound = overflowError -- Note [Order of tests]
| otherwise = (I64# (x# `divInt#` y#), I64# (x# `modInt#` y#))
toInteger (I64# x#) = smallInteger x#
range (m,n) = [m..n]
unsafeIndex (m,_) i = fromIntegral i - fromIntegral m
inRange (m,n) i = m <= i && i <= n
+
+{-
+Note [Order of tests]
+
+Suppose we had a definition like:
+
+ quot x y
+ | y == 0 = divZeroError
+ | x == minBound && y == (-1) = overflowError
+ | otherwise = x `primQuot` y
+
+Note in particular that the
+ x == minBound
+test comes before the
+ y == (-1)
+test.
+
+this expands to something like:
+
+ case y of
+ 0 -> divZeroError
+ _ -> case x of
+ -9223372036854775808 ->
+ case y of
+ -1 -> overflowError
+ _ -> x `primQuot` y
+ _ -> x `primQuot` y
+
+Now if we have the call (x `quot` 2), and quot gets inlined, then we get:
+
+ case 2 of
+ 0 -> divZeroError
+ _ -> case x of
+ -9223372036854775808 ->
+ case 2 of
+ -1 -> overflowError
+ _ -> x `primQuot` 2
+ _ -> x `primQuot` 2
+
+which simplifies to:
+
+ case x of
+ -9223372036854775808 -> x `primQuot` 2
+ _ -> x `primQuot` 2
+
+Now we have a case with two identical branches, which would be
+eliminated (assuming it doesn't affect strictness, which it doesn't in
+this case), leaving the desired:
+
+ x `primQuot` 2
+
+except in the minBound branch we know what x is, and GHC cleverly does
+the division at compile time, giving:
+
+ case x of
+ -9223372036854775808 -> -4611686018427387904
+ _ -> x `primQuot` 2
+
+So instead we use a definition like:
+
+ quot x y
+ | y == 0 = divZeroError
+ | y == (-1) && x == minBound = overflowError
+ | otherwise = x `primQuot` y
+
+which gives us:
+
+ case y of
+ 0 -> divZeroError
+ -1 ->
+ case x of
+ -9223372036854775808 -> overflowError
+ _ -> x `primQuot` y
+ _ -> x `primQuot` y
+
+for which our call (x `quot` 2) expands to:
+
+ case 2 of
+ 0 -> divZeroError
+ -1 ->
+ case x of
+ -9223372036854775808 -> overflowError
+ _ -> x `primQuot` 2
+ _ -> x `primQuot` 2
+
+which simplifies to:
+
+ x `primQuot` 2
+
+as required.
+
+
+
+But we now have the same problem with a constant numerator: the call
+(2 `quot` y) expands to
+
+ case y of
+ 0 -> divZeroError
+ -1 ->
+ case 2 of
+ -9223372036854775808 -> overflowError
+ _ -> 2 `primQuot` y
+ _ -> 2 `primQuot` y
+
+which simplifies to:
+
+ case y of
+ 0 -> divZeroError
+ -1 -> 2 `primQuot` y
+ _ -> 2 `primQuot` y
+
+which simplifies to:
+
+ case y of
+ 0 -> divZeroError
+ -1 -> -2
+ _ -> 2 `primQuot` y
+
+
+However, constant denominators are more common than constant numerators,
+so the
+ y == (-1) && x == minBound
+order gives us better code in the common case.
+-}
+
projects / ghc-base.git / blobdiff