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diff --git a/compiler/codeGen/Bitmap.hs b/compiler/codeGen/Bitmap.hs
new file mode 100644
index 0000000000..c0b490978c
--- /dev/null
+++ b/compiler/codeGen/Bitmap.hs
@@ -0,0 +1,79 @@
+--
+-- (c) The University of Glasgow 2003
+-- 
+
+-- Functions for constructing bitmaps, which are used in various
+-- places in generated code (stack frame liveness masks, function
+-- argument liveness masks, SRT bitmaps).
+
+module Bitmap ( 
+	Bitmap, mkBitmap,
+	intsToBitmap, intsToReverseBitmap,
+	mAX_SMALL_BITMAP_SIZE
+  ) where
+
+#include "HsVersions.h"
+#include "../includes/MachDeps.h"
+
+import SMRep
+import Constants
+import DATA_BITS
+
+{-|
+A bitmap represented by a sequence of 'StgWord's on the /target/
+architecture.  These are used for bitmaps in info tables and other
+generated code which need to be emitted as sequences of StgWords.
+-}
+type Bitmap = [StgWord]
+
+-- | Make a bitmap from a sequence of bits
+mkBitmap :: [Bool] -> Bitmap
+mkBitmap [] = []
+mkBitmap stuff = chunkToBitmap chunk : mkBitmap rest
+  where (chunk, rest) = splitAt wORD_SIZE_IN_BITS stuff
+
+chunkToBitmap :: [Bool] -> StgWord
+chunkToBitmap chunk = 
+  foldr (.|.) 0 [ 1 `shiftL` n | (True,n) <- zip chunk [0..] ]
+
+-- | Make a bitmap where the slots specified are the /ones/ in the bitmap.
+-- eg. @[1,2,4], size 4 ==> 0xb@.
+--
+-- The list of @Int@s /must/ be already sorted.
+intsToBitmap :: Int -> [Int] -> Bitmap
+intsToBitmap size slots{- must be sorted -}
+  | size <= 0 = []
+  | otherwise = 
+    (foldr (.|.) 0 (map (1 `shiftL`) these)) : 
+	intsToBitmap (size - wORD_SIZE_IN_BITS) 
+	     (map (\x -> x - wORD_SIZE_IN_BITS) rest)
+   where (these,rest) = span (<wORD_SIZE_IN_BITS) slots
+
+-- | Make a bitmap where the slots specified are the /zeros/ in the bitmap.
+-- eg. @[1,2,4], size 4 ==> 0x8@  (we leave any bits outside the size as zero,
+-- just to make the bitmap easier to read).
+--
+-- The list of @Int@s /must/ be already sorted.
+intsToReverseBitmap :: Int -> [Int] -> Bitmap
+intsToReverseBitmap size slots{- must be sorted -}
+  | size <= 0 = []
+  | otherwise = 
+    (foldr xor init (map (1 `shiftL`) these)) : 
+	intsToReverseBitmap (size - wORD_SIZE_IN_BITS) 
+	     (map (\x -> x - wORD_SIZE_IN_BITS) rest)
+   where (these,rest) = span (<wORD_SIZE_IN_BITS) slots
+	 init
+	   | size >= wORD_SIZE_IN_BITS = complement 0
+	   | otherwise                 = (1 `shiftL` size) - 1
+
+{- |
+Magic number, must agree with @BITMAP_BITS_SHIFT@ in InfoTables.h.
+Some kinds of bitmap pack a size\/bitmap into a single word if
+possible, or fall back to an external pointer when the bitmap is too
+large.  This value represents the largest size of bitmap that can be
+packed into a single word.
+-}
+mAX_SMALL_BITMAP_SIZE :: Int
+mAX_SMALL_BITMAP_SIZE  | wORD_SIZE == 4 = 27
+		       | otherwise      = 58
+