[Git][ghc/ghc][master] Use static array in zeroCount

[Marge Bot]

 Marge Bot pushed to branch master at Glasgow Haskell Compiler / GHC


Commits:
4af6126d by Sylvain Henry at 2020-12-11T22:44:11-05:00
Use static array in zeroCount

- - - - -


1 changed file:

- libraries/base/GHC/Float/ConversionUtils.hs


Changes:

=====================================
libraries/base/GHC/Float/ConversionUtils.hs
=====================================
@@ -33,13 +33,10 @@ default ()
 
 #define TO64    integerToInt64#
 
-toByte64# :: Int64# -> Int#
-toByte64# i = word2Int# (and# 255## (int2Word# (int64ToInt# i)))
-
 -- Double mantissae have 53 bits, too much for Int#
 elim64# :: Int64# -> Int# -> (# Integer, Int# #)
 elim64# n e =
-    case zeroCount (toByte64# n) of
+    case zeroCount (int64ToInt# n) of
       t | isTrue# (e <=# t) -> (# integerFromInt64# (uncheckedIShiftRA64# n e), 0# #)
         | isTrue# (t <# 8#) -> (# integerFromInt64# (uncheckedIShiftRA64# n t), e -# t #)
         | otherwise         -> elim64# (uncheckedIShiftRA64# n 8#) (e -# 8#)
@@ -60,41 +57,13 @@ elimZerosInteger m e = elim64# (TO64 m) e
 
 elimZerosInt# :: Int# -> Int# -> (# Integer, Int# #)
 elimZerosInt# n e =
-    case zeroCount (toByte# n) of
+    case zeroCount n of
       t | isTrue# (e <=# t) -> (# IS (uncheckedIShiftRA# n e), 0# #)
         | isTrue# (t <# 8#) -> (# IS (uncheckedIShiftRA# n t), e -# t #)
         | otherwise         -> elimZerosInt# (uncheckedIShiftRA# n 8#) (e -# 8#)
 
-{-# INLINE zeroCount #-}
+-- | Number of trailing zero bits in a byte
 zeroCount :: Int# -> Int#
-zeroCount i =
-    case zeroCountArr of
-      BA ba -> indexInt8Array# ba i
-
-toByte# :: Int# -> Int#
-toByte# i = word2Int# (and# 255## (int2Word# i))
-
-
-data BA = BA ByteArray#
-
--- Number of trailing zero bits in a byte
-zeroCountArr :: BA
-zeroCountArr =
-    let mkArr s =
-          case newByteArray# 256# s of
-            (# s1, mba #) ->
-              case writeInt8Array# mba 0# 8# s1 of
-                s2 ->
-                  let fillA step val idx st
-                        | isTrue# (idx <# 256#) =
-                                        case writeInt8Array# mba idx val st of
-                                          nx -> fillA step val (idx +# step) nx
-                        | isTrue# (step <# 256#) =
-                                        fillA (2# *# step) (val +# 1#) step  st
-                        | otherwise   = st
-                  in case fillA 2# 0# 1# s2 of
-                       s3 -> case unsafeFreezeByteArray# mba s3 of
-                                (# _, ba #) -> ba
-    in case mkArr realWorld# of
-        b -> BA b
-
+zeroCount i = indexInt8OffAddr# arr (word2Int# (narrow8Word# (int2Word# i))) -- index must be in [0,255]
+  where
+    arr = "\8\0\1\0\2\0\1\0\3\0\1\0\2\0\1\0\4\0\1\0\2\0\1\0\3\0\1\0\2\0\1\0\5\0\1\0\2\0\1\0\3\0\1\0\2\0\1\0\4\0\1\0\2\0\1\0\3\0\1\0\2\0\1\0\6\0\1\0\2\0\1\0\3\0\1\0\2\0\1\0\4\0\1\0\2\0\1\0\3\0\1\0\2\0\1\0\5\0\1\0\2\0\1\0\3\0\1\0\2\0\1\0\4\0\1\0\2\0\1\0\3\0\1\0\2\0\1\0\7\0\1\0\2\0\1\0\3\0\1\0\2\0\1\0\4\0\1\0\2\0\1\0\3\0\1\0\2\0\1\0\5\0\1\0\2\0\1\0\3\0\1\0\2\0\1\0\4\0\1\0\2\0\1\0\3\0\1\0\2\0\1\0\6\0\1\0\2\0\1\0\3\0\1\0\2\0\1\0\4\0\1\0\2\0\1\0\3\0\1\0\2\0\1\0\5\0\1\0\2\0\1\0\3\0\1\0\2\0\1\0\4\0\1\0\2\0\1\0\3\0\1\0\2\0\1\0"#



View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/4af6126d1758d5e365cadf032e34c99489f13dee

-- 
View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/4af6126d1758d5e365cadf032e34c99489f13dee
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