\begin{code}
-{-# OPTIONS -fno-implicit-prelude #-}
+{-# LANGUAGE NoImplicitPrelude, BangPatterns, MagicHash #-}
+{-# OPTIONS_HADDOCK hide #-}
-----------------------------------------------------------------------------
-- |
-- Module : GHC.Enum
--
-----------------------------------------------------------------------------
+-- #hide
module GHC.Enum(
- Bounded(..), Enum(..),
- boundedEnumFrom, boundedEnumFromThen,
+ Bounded(..), Enum(..),
+ boundedEnumFrom, boundedEnumFromThen,
- -- Instances for Bounded and Enum: (), Char, Int
+ -- Instances for Bounded and Enum: (), Char, Int
) where
-import {-# SOURCE #-} GHC.Err ( error )
import GHC.Base
-import Data.Tuple () -- for dependencies
-default () -- Double isn't available yet
+import Data.Tuple () -- for dependencies
+default () -- Double isn't available yet
\end{code}
%*********************************************************
-%* *
+%* *
\subsection{Class declarations}
-%* *
+%* *
%*********************************************************
\begin{code}
-- * 'enumFrom' and 'enumFromThen' should be defined with an implicit bound,
-- thus:
--
--- > enumFrom x = enumFromTo x maxBound
--- > enumFromThen x y = enumFromThenTo x y bound
--- > where
--- > bound | fromEnum y >= fromEnum x = maxBound
--- > | otherwise = minBound
+-- > enumFrom x = enumFromTo x maxBound
+-- > enumFromThen x y = enumFromThenTo x y bound
+-- > where
+-- > bound | fromEnum y >= fromEnum x = maxBound
+-- > | otherwise = minBound
--
-class Enum a where
+class Enum a where
-- | the successor of a value. For numeric types, 'succ' adds 1.
- succ :: a -> a
+ succ :: a -> a
-- | the predecessor of a value. For numeric types, 'pred' subtracts 1.
- pred :: a -> a
+ pred :: a -> a
-- | Convert from an 'Int'.
toEnum :: Int -> a
-- | Convert to an 'Int'.
fromEnum :: a -> Int
-- | Used in Haskell's translation of @[n..]@.
- enumFrom :: a -> [a]
+ enumFrom :: a -> [a]
-- | Used in Haskell's translation of @[n,n'..]@.
- enumFromThen :: a -> a -> [a]
+ enumFromThen :: a -> a -> [a]
-- | Used in Haskell's translation of @[n..m]@.
- enumFromTo :: a -> a -> [a]
+ enumFromTo :: a -> a -> [a]
-- | Used in Haskell's translation of @[n,n'..m]@.
- enumFromThenTo :: a -> a -> a -> [a]
+ enumFromThenTo :: a -> a -> a -> [a]
- succ = toEnum . (`plusInt` oneInt) . fromEnum
- pred = toEnum . (`minusInt` oneInt) . fromEnum
- enumFrom x = map toEnum [fromEnum x ..]
- enumFromThen x y = map toEnum [fromEnum x, fromEnum y ..]
+ succ = toEnum . (`plusInt` oneInt) . fromEnum
+ pred = toEnum . (`minusInt` oneInt) . fromEnum
+ enumFrom x = map toEnum [fromEnum x ..]
+ enumFromThen x y = map toEnum [fromEnum x, fromEnum y ..]
enumFromTo x y = map toEnum [fromEnum x .. fromEnum y]
enumFromThenTo x1 x2 y = map toEnum [fromEnum x1, fromEnum x2 .. fromEnum y]
%*********************************************************
-%* *
+%* *
\subsection{Tuples}
-%* *
+%* *
%*********************************************************
\begin{code}
| otherwise = error "Prelude.Enum.().toEnum: bad argument"
fromEnum () = zeroInt
- enumFrom () = [()]
- enumFromThen () () = [()]
- enumFromTo () () = [()]
- enumFromThenTo () () () = [()]
+ enumFrom () = [()]
+ enumFromThen () () = let many = ():many in many
+ enumFromTo () () = [()]
+ enumFromThenTo () () () = let many = ():many in many
\end{code}
\begin{code}
+-- Report requires instances up to 15
instance (Bounded a, Bounded b) => Bounded (a,b) where
minBound = (minBound, minBound)
maxBound = (maxBound, maxBound)
instance (Bounded a, Bounded b, Bounded c, Bounded d) => Bounded (a,b,c,d) where
minBound = (minBound, minBound, minBound, minBound)
maxBound = (maxBound, maxBound, maxBound, maxBound)
+
+instance (Bounded a, Bounded b, Bounded c, Bounded d, Bounded e) => Bounded (a,b,c,d,e) where
+ minBound = (minBound, minBound, minBound, minBound, minBound)
+ maxBound = (maxBound, maxBound, maxBound, maxBound, maxBound)
+
+instance (Bounded a, Bounded b, Bounded c, Bounded d, Bounded e, Bounded f)
+ => Bounded (a,b,c,d,e,f) where
+ minBound = (minBound, minBound, minBound, minBound, minBound, minBound)
+ maxBound = (maxBound, maxBound, maxBound, maxBound, maxBound, maxBound)
+
+instance (Bounded a, Bounded b, Bounded c, Bounded d, Bounded e, Bounded f, Bounded g)
+ => Bounded (a,b,c,d,e,f,g) where
+ minBound = (minBound, minBound, minBound, minBound, minBound, minBound, minBound)
+ maxBound = (maxBound, maxBound, maxBound, maxBound, maxBound, maxBound, maxBound)
+
+instance (Bounded a, Bounded b, Bounded c, Bounded d, Bounded e, Bounded f, Bounded g,
+ Bounded h)
+ => Bounded (a,b,c,d,e,f,g,h) where
+ minBound = (minBound, minBound, minBound, minBound, minBound, minBound, minBound, minBound)
+ maxBound = (maxBound, maxBound, maxBound, maxBound, maxBound, maxBound, maxBound, maxBound)
+
+instance (Bounded a, Bounded b, Bounded c, Bounded d, Bounded e, Bounded f, Bounded g,
+ Bounded h, Bounded i)
+ => Bounded (a,b,c,d,e,f,g,h,i) where
+ minBound = (minBound, minBound, minBound, minBound, minBound, minBound, minBound, minBound,
+ minBound)
+ maxBound = (maxBound, maxBound, maxBound, maxBound, maxBound, maxBound, maxBound, maxBound,
+ maxBound)
+
+instance (Bounded a, Bounded b, Bounded c, Bounded d, Bounded e, Bounded f, Bounded g,
+ Bounded h, Bounded i, Bounded j)
+ => Bounded (a,b,c,d,e,f,g,h,i,j) where
+ minBound = (minBound, minBound, minBound, minBound, minBound, minBound, minBound, minBound,
+ minBound, minBound)
+ maxBound = (maxBound, maxBound, maxBound, maxBound, maxBound, maxBound, maxBound, maxBound,
+ maxBound, maxBound)
+
+instance (Bounded a, Bounded b, Bounded c, Bounded d, Bounded e, Bounded f, Bounded g,
+ Bounded h, Bounded i, Bounded j, Bounded k)
+ => Bounded (a,b,c,d,e,f,g,h,i,j,k) where
+ minBound = (minBound, minBound, minBound, minBound, minBound, minBound, minBound, minBound,
+ minBound, minBound, minBound)
+ maxBound = (maxBound, maxBound, maxBound, maxBound, maxBound, maxBound, maxBound, maxBound,
+ maxBound, maxBound, maxBound)
+
+instance (Bounded a, Bounded b, Bounded c, Bounded d, Bounded e, Bounded f, Bounded g,
+ Bounded h, Bounded i, Bounded j, Bounded k, Bounded l)
+ => Bounded (a,b,c,d,e,f,g,h,i,j,k,l) where
+ minBound = (minBound, minBound, minBound, minBound, minBound, minBound, minBound, minBound,
+ minBound, minBound, minBound, minBound)
+ maxBound = (maxBound, maxBound, maxBound, maxBound, maxBound, maxBound, maxBound, maxBound,
+ maxBound, maxBound, maxBound, maxBound)
+
+instance (Bounded a, Bounded b, Bounded c, Bounded d, Bounded e, Bounded f, Bounded g,
+ Bounded h, Bounded i, Bounded j, Bounded k, Bounded l, Bounded m)
+ => Bounded (a,b,c,d,e,f,g,h,i,j,k,l,m) where
+ minBound = (minBound, minBound, minBound, minBound, minBound, minBound, minBound, minBound,
+ minBound, minBound, minBound, minBound, minBound)
+ maxBound = (maxBound, maxBound, maxBound, maxBound, maxBound, maxBound, maxBound, maxBound,
+ maxBound, maxBound, maxBound, maxBound, maxBound)
+
+instance (Bounded a, Bounded b, Bounded c, Bounded d, Bounded e, Bounded f, Bounded g,
+ Bounded h, Bounded i, Bounded j, Bounded k, Bounded l, Bounded m, Bounded n)
+ => Bounded (a,b,c,d,e,f,g,h,i,j,k,l,m,n) where
+ minBound = (minBound, minBound, minBound, minBound, minBound, minBound, minBound, minBound,
+ minBound, minBound, minBound, minBound, minBound, minBound)
+ maxBound = (maxBound, maxBound, maxBound, maxBound, maxBound, maxBound, maxBound, maxBound,
+ maxBound, maxBound, maxBound, maxBound, maxBound, maxBound)
+
+instance (Bounded a, Bounded b, Bounded c, Bounded d, Bounded e, Bounded f, Bounded g,
+ Bounded h, Bounded i, Bounded j, Bounded k, Bounded l, Bounded m, Bounded n, Bounded o)
+ => Bounded (a,b,c,d,e,f,g,h,i,j,k,l,m,n,o) where
+ minBound = (minBound, minBound, minBound, minBound, minBound, minBound, minBound, minBound,
+ minBound, minBound, minBound, minBound, minBound, minBound, minBound)
+ maxBound = (maxBound, maxBound, maxBound, maxBound, maxBound, maxBound, maxBound, maxBound,
+ maxBound, maxBound, maxBound, maxBound, maxBound, maxBound, maxBound)
\end{code}
%*********************************************************
-%* *
+%* *
\subsection{Type @Bool@}
-%* *
+%* *
%*********************************************************
\begin{code}
pred False = error "Prelude.Enum.Bool.pred: bad argument"
toEnum n | n == zeroInt = False
- | n == oneInt = True
- | otherwise = error "Prelude.Enum.Bool.toEnum: bad argument"
+ | n == oneInt = True
+ | otherwise = error "Prelude.Enum.Bool.toEnum: bad argument"
fromEnum False = zeroInt
fromEnum True = oneInt
\end{code}
%*********************************************************
-%* *
+%* *
\subsection{Type @Ordering@}
-%* *
+%* *
%*********************************************************
\begin{code}
pred LT = error "Prelude.Enum.Ordering.pred: bad argument"
toEnum n | n == zeroInt = LT
- | n == oneInt = EQ
- | n == twoInt = GT
+ | n == oneInt = EQ
+ | n == twoInt = GT
toEnum _ = error "Prelude.Enum.Ordering.toEnum: bad argument"
fromEnum LT = zeroInt
\end{code}
%*********************************************************
-%* *
+%* *
\subsection{Type @Char@}
-%* *
+%* *
%*********************************************************
\begin{code}
instance Enum Char where
succ (C# c#)
| not (ord# c# ==# 0x10FFFF#) = C# (chr# (ord# c# +# 1#))
- | otherwise = error ("Prelude.Enum.Char.succ: bad argument")
+ | otherwise = error ("Prelude.Enum.Char.succ: bad argument")
pred (C# c#)
| not (ord# c# ==# 0#) = C# (chr# (ord# c# -# 1#))
- | otherwise = error ("Prelude.Enum.Char.pred: bad argument")
+ | otherwise = error ("Prelude.Enum.Char.pred: bad argument")
toEnum = chr
fromEnum = ord
{-# INLINE enumFrom #-}
enumFrom (C# x) = eftChar (ord# x) 0x10FFFF#
- -- Blarg: technically I guess enumFrom isn't strict!
+ -- Blarg: technically I guess enumFrom isn't strict!
{-# INLINE enumFromTo #-}
enumFromTo (C# x) (C# y) = eftChar (ord# x) (ord# y)
enumFromThenTo (C# x1) (C# x2) (C# y) = efdtChar (ord# x1) (ord# x2) (ord# y)
{-# RULES
-"eftChar" [~1] forall x y. eftChar x y = build (\c n -> eftCharFB c n x y)
-"efdChar" [~1] forall x1 x2. efdChar x1 x2 = build (\ c n -> efdCharFB c n x1 x2)
-"efdtChar" [~1] forall x1 x2 l. efdtChar x1 x2 l = build (\ c n -> efdtCharFB c n x1 x2 l)
-"eftCharList" [1] eftCharFB (:) [] = eftChar
-"efdCharList" [1] efdCharFB (:) [] = efdChar
-"efdtCharList" [1] efdtCharFB (:) [] = efdtChar
+"eftChar" [~1] forall x y. eftChar x y = build (\c n -> eftCharFB c n x y)
+"efdChar" [~1] forall x1 x2. efdChar x1 x2 = build (\ c n -> efdCharFB c n x1 x2)
+"efdtChar" [~1] forall x1 x2 l. efdtChar x1 x2 l = build (\ c n -> efdtCharFB c n x1 x2 l)
+"eftCharList" [1] eftCharFB (:) [] = eftChar
+"efdCharList" [1] efdCharFB (:) [] = efdChar
+"efdtCharList" [1] efdtCharFB (:) [] = efdtChar
#-}
-- We can do better than for Ints because we don't
-- have hassles about arithmetic overflow at maxBound
{-# INLINE [0] eftCharFB #-}
-eftCharFB c n x y = go x
- where
- go x | x ># y = n
- | otherwise = C# (chr# x) `c` go (x +# 1#)
+eftCharFB :: (Char -> a -> a) -> a -> Int# -> Int# -> a
+eftCharFB c n x0 y = go x0
+ where
+ go x | x ># y = n
+ | otherwise = C# (chr# x) `c` go (x +# 1#)
-eftChar x y | x ># y = []
- | otherwise = C# (chr# x) : eftChar (x +# 1#) y
+eftChar :: Int# -> Int# -> String
+eftChar x y | x ># y = []
+ | otherwise = C# (chr# x) : eftChar (x +# 1#) y
-- For enumFromThenTo we give up on inlining
{-# NOINLINE [0] efdCharFB #-}
+efdCharFB :: (Char -> a -> a) -> a -> Int# -> Int# -> a
efdCharFB c n x1 x2
| delta >=# 0# = go_up_char_fb c n x1 delta 0x10FFFF#
| otherwise = go_dn_char_fb c n x1 delta 0#
where
- delta = x2 -# x1
+ !delta = x2 -# x1
+efdChar :: Int# -> Int# -> String
efdChar x1 x2
| delta >=# 0# = go_up_char_list x1 delta 0x10FFFF#
| otherwise = go_dn_char_list x1 delta 0#
where
- delta = x2 -# x1
+ !delta = x2 -# x1
{-# NOINLINE [0] efdtCharFB #-}
+efdtCharFB :: (Char -> a -> a) -> a -> Int# -> Int# -> Int# -> a
efdtCharFB c n x1 x2 lim
| delta >=# 0# = go_up_char_fb c n x1 delta lim
| otherwise = go_dn_char_fb c n x1 delta lim
where
- delta = x2 -# x1
+ !delta = x2 -# x1
+efdtChar :: Int# -> Int# -> Int# -> String
efdtChar x1 x2 lim
| delta >=# 0# = go_up_char_list x1 delta lim
| otherwise = go_dn_char_list x1 delta lim
where
- delta = x2 -# x1
+ !delta = x2 -# x1
-go_up_char_fb c n x delta lim
- = go_up x
+go_up_char_fb :: (Char -> a -> a) -> a -> Int# -> Int# -> Int# -> a
+go_up_char_fb c n x0 delta lim
+ = go_up x0
where
go_up x | x ># lim = n
- | otherwise = C# (chr# x) `c` go_up (x +# delta)
+ | otherwise = C# (chr# x) `c` go_up (x +# delta)
-go_dn_char_fb c n x delta lim
- = go_dn x
+go_dn_char_fb :: (Char -> a -> a) -> a -> Int# -> Int# -> Int# -> a
+go_dn_char_fb c n x0 delta lim
+ = go_dn x0
where
go_dn x | x <# lim = n
- | otherwise = C# (chr# x) `c` go_dn (x +# delta)
+ | otherwise = C# (chr# x) `c` go_dn (x +# delta)
-go_up_char_list x delta lim
- = go_up x
+go_up_char_list :: Int# -> Int# -> Int# -> String
+go_up_char_list x0 delta lim
+ = go_up x0
where
go_up x | x ># lim = []
- | otherwise = C# (chr# x) : go_up (x +# delta)
+ | otherwise = C# (chr# x) : go_up (x +# delta)
-go_dn_char_list x delta lim
- = go_dn x
+go_dn_char_list :: Int# -> Int# -> Int# -> String
+go_dn_char_list x0 delta lim
+ = go_dn x0
where
go_dn x | x <# lim = []
- | otherwise = C# (chr# x) : go_dn (x +# delta)
+ | otherwise = C# (chr# x) : go_dn (x +# delta)
\end{code}
%*********************************************************
-%* *
+%* *
\subsection{Type @Int@}
-%* *
+%* *
%*********************************************************
Be careful about these instances.
- (a) remember that you have to count down as well as up e.g. [13,12..0]
- (b) be careful of Int overflow
- (c) remember that Int is bounded, so [1..] terminates at maxInt
+ (a) remember that you have to count down as well as up e.g. [13,12..0]
+ (b) be careful of Int overflow
+ (c) remember that Int is bounded, so [1..] terminates at maxInt
Also NB that the Num class isn't available in this module.
-
+
\begin{code}
instance Bounded Int where
minBound = minInt
{-# INLINE enumFrom #-}
enumFrom (I# x) = eftInt x maxInt#
- where I# maxInt# = maxInt
- -- Blarg: technically I guess enumFrom isn't strict!
+ where !(I# maxInt#) = maxInt
+ -- Blarg: technically I guess enumFrom isn't strict!
{-# INLINE enumFromTo #-}
enumFromTo (I# x) (I# y) = eftInt x y
-- In particular, we have rules for deforestation
{-# RULES
-"eftInt" [~1] forall x y. eftInt x y = build (\ c n -> eftIntFB c n x y)
-"eftIntList" [1] eftIntFB (:) [] = eftInt
+"eftInt" [~1] forall x y. eftInt x y = build (\ c n -> eftIntFB c n x y)
+"eftIntList" [1] eftIntFB (:) [] = eftInt
#-}
eftInt :: Int# -> Int# -> [Int]
-- [x1..x2]
-eftInt x y | x ># y = []
- | otherwise = go x
- where
- go x = I# x : if x ==# y then [] else go (x +# 1#)
+eftInt x0 y | x0 ># y = []
+ | otherwise = go x0
+ where
+ go x = I# x : if x ==# y then [] else go (x +# 1#)
{-# INLINE [0] eftIntFB #-}
eftIntFB :: (Int -> r -> r) -> r -> Int# -> Int# -> r
-eftIntFB c n x y | x ># y = n
- | otherwise = go x
- where
- go x = I# x `c` if x ==# y then n else go (x +# 1#)
- -- Watch out for y=maxBound; hence ==, not >
- -- Be very careful not to have more than one "c"
- -- so that when eftInfFB is inlined we can inline
- -- whatver is bound to "c"
+eftIntFB c n x0 y | x0 ># y = n
+ | otherwise = go x0
+ where
+ go x = I# x `c` if x ==# y then n else go (x +# 1#)
+ -- Watch out for y=maxBound; hence ==, not >
+ -- Be very careful not to have more than one "c"
+ -- so that when eftInfFB is inlined we can inline
+ -- whatever is bound to "c"
-----------------------------------------------------
--- efdInt and efdtInt deal with [a,b..] and [a,b..c], which are much less common
--- so we are less elaborate. The code is more complicated anyway, because
--- of worries about Int overflow, so we don't both with rules and deforestation
+-- efdInt and efdtInt deal with [a,b..] and [a,b..c].
+-- The code is more complicated because of worries about Int overflow.
+
+{-# RULES
+"efdtInt" [~1] forall x1 x2 y.
+ efdtInt x1 x2 y = build (\ c n -> efdtIntFB c n x1 x2 y)
+"efdtIntUpList" [1] efdtIntFB (:) [] = efdtInt
+ #-}
efdInt :: Int# -> Int# -> [Int]
-- [x1,x2..maxInt]
efdInt x1 x2
- | x2 >=# x1 = case maxInt of I# y -> efdtIntUp x1 x2 y
- | otherwise = case minInt of I# y -> efdtIntDn x1 x2 y
+ | x2 >=# x1 = case maxInt of I# y -> efdtIntUp x1 x2 y
+ | otherwise = case minInt of I# y -> efdtIntDn x1 x2 y
efdtInt :: Int# -> Int# -> Int# -> [Int]
-- [x1,x2..y]
efdtInt x1 x2 y
- | x2 >=# x1 = efdtIntUp x1 x2 y
- | otherwise = efdtIntDn x1 x2 y
+ | x2 >=# x1 = efdtIntUp x1 x2 y
+ | otherwise = efdtIntDn x1 x2 y
+
+{-# INLINE [0] efdtIntFB #-}
+efdtIntFB :: (Int -> r -> r) -> r -> Int# -> Int# -> Int# -> r
+efdtIntFB c n x1 x2 y
+ | x2 >=# x1 = efdtIntUpFB c n x1 x2 y
+ | otherwise = efdtIntDnFB c n x1 x2 y
+-- Requires x2 >= x1
efdtIntUp :: Int# -> Int# -> Int# -> [Int]
-efdtIntUp x1 x2 y -- Be careful about overflow!
- | y <# x2 = if y <# x1 then [] else [I# x1]
- | otherwise
- = -- Common case: x1 < x2 <= y
- let
- delta = x2 -# x1
- y' = y -# delta
- -- NB: x1 <= y'; hence y' is representable
-
- -- Invariant: x <= y; and x+delta won't overflow
- go_up x | x ># y' = [I# x]
- | otherwise = I# x : go_up (x +# delta)
- in
- I# x1 : go_up x2
-
+efdtIntUp x1 x2 y -- Be careful about overflow!
+ | y <# x2 = if y <# x1 then [] else [I# x1]
+ | otherwise = -- Common case: x1 <= x2 <= y
+ let !delta = x2 -# x1 -- >= 0
+ !y' = y -# delta -- x1 <= y' <= y; hence y' is representable
+
+ -- Invariant: x <= y
+ -- Note that: z <= y' => z + delta won't overflow
+ -- so we are guaranteed not to overflow if/when we recurse
+ go_up x | x ># y' = [I# x]
+ | otherwise = I# x : go_up (x +# delta)
+ in I# x1 : go_up x2
+
+-- Requires x2 >= x1
+efdtIntUpFB :: (Int -> r -> r) -> r -> Int# -> Int# -> Int# -> r
+efdtIntUpFB c n x1 x2 y -- Be careful about overflow!
+ | y <# x2 = if y <# x1 then n else I# x1 `c` n
+ | otherwise = -- Common case: x1 <= x2 <= y
+ let !delta = x2 -# x1 -- >= 0
+ !y' = y -# delta -- x1 <= y' <= y; hence y' is representable
+
+ -- Invariant: x <= y
+ -- Note that: z <= y' => z + delta won't overflow
+ -- so we are guaranteed not to overflow if/when we recurse
+ go_up x | x ># y' = I# x `c` n
+ | otherwise = I# x `c` go_up (x +# delta)
+ in I# x1 `c` go_up x2
+
+-- Requires x2 <= x1
efdtIntDn :: Int# -> Int# -> Int# -> [Int]
-efdtIntDn x1 x2 y -- x2 < x1
- | y ># x2 = if y ># x1 then [] else [I# x1]
- | otherwise
- = -- Common case: x1 > x2 >= y
- let
- delta = x2 -# x1
- y' = y -# delta
- -- NB: x1 <= y'; hence y' is representable
-
- -- Invariant: x >= y; and x+delta won't overflow
- go_dn x | x <# y' = [I# x]
- | otherwise = I# x : go_dn (x +# delta)
- in
- I# x1 : go_dn x2
+efdtIntDn x1 x2 y -- Be careful about underflow!
+ | y ># x2 = if y ># x1 then [] else [I# x1]
+ | otherwise = -- Common case: x1 >= x2 >= y
+ let !delta = x2 -# x1 -- <= 0
+ !y' = y -# delta -- y <= y' <= x1; hence y' is representable
+
+ -- Invariant: x >= y
+ -- Note that: z >= y' => z + delta won't underflow
+ -- so we are guaranteed not to underflow if/when we recurse
+ go_dn x | x <# y' = [I# x]
+ | otherwise = I# x : go_dn (x +# delta)
+ in I# x1 : go_dn x2
+
+-- Requires x2 <= x1
+efdtIntDnFB :: (Int -> r -> r) -> r -> Int# -> Int# -> Int# -> r
+efdtIntDnFB c n x1 x2 y -- Be careful about underflow!
+ | y ># x2 = if y ># x1 then n else I# x1 `c` n
+ | otherwise = -- Common case: x1 >= x2 >= y
+ let !delta = x2 -# x1 -- <= 0
+ !y' = y -# delta -- y <= y' <= x1; hence y' is representable
+
+ -- Invariant: x >= y
+ -- Note that: z >= y' => z + delta won't underflow
+ -- so we are guaranteed not to underflow if/when we recurse
+ go_dn x | x <# y' = I# x `c` n
+ | otherwise = I# x `c` go_dn (x +# delta)
+ in I# x1 `c` go_dn x2
\end{code}
projects / ghc-base.git / blobdiff