cmm/Bitmap.hs

    --
    -- (c) The University of Glasgow 2003-2006
    --

    -- 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,
            seqBitmap,
      ) where

    #include "HsVersions.h"
    #include "../includes/MachDeps.h"

    import SMRep
    import DynFlags
    import Util

    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 :: DynFlags -> [Bool] -> Bitmap
    mkBitmap _ [] = []
    mkBitmap dflags stuff = chunkToBitmap dflags chunk : mkBitmap dflags rest
      where (chunk, rest) = splitAt (wORD_SIZE_IN_BITS dflags) stuff

    chunkToBitmap :: DynFlags -> [Bool] -> StgWord
    chunkToBitmap dflags chunk =
      foldr (.|.) (toStgWord dflags 0) [ toStgWord dflags 1 `shiftL` n | (True,n) <- zip chunk [0..] ]

    -- | Make a bitmap where the slots specified are the /ones/ in the bitmap.
    -- eg. @[0,1,3], size 4 ==> 0xb@.
    --
    -- The list of @Int@s /must/ be already sorted.
    intsToBitmap :: DynFlags -> Int -> [Int] -> Bitmap
    intsToBitmap dflags size slots{- must be sorted -}
      | size <= 0 = []
      | otherwise =
        (foldr (.|.) (toStgWord dflags 0) (map (toStgWord dflags 1 `shiftL`) these)) :
            intsToBitmap dflags (size - wORD_SIZE_IN_BITS dflags)
                 (map (\x -> x - wORD_SIZE_IN_BITS dflags) rest)
       where (these,rest) = span (< wORD_SIZE_IN_BITS dflags) slots

    -- | Make a bitmap where the slots specified are the /zeros/ in the bitmap.
    -- eg. @[0,1,3], size 4 ==> 0x4@  (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 and duplicate-free.
    intsToReverseBitmap :: DynFlags -> Int -> [Int] -> Bitmap
    intsToReverseBitmap dflags size slots{- must be sorted -}
      | size <= 0 = []
      | otherwise =
        (foldr xor (toStgWord dflags init) (map (toStgWord dflags 1 `shiftL`) these)) :
            intsToReverseBitmap dflags (size - wORD_SIZE_IN_BITS dflags)
                 (map (\x -> x - wORD_SIZE_IN_BITS dflags) rest)
       where (these,rest) = span (< wORD_SIZE_IN_BITS dflags) slots
             init
               | size >= wORD_SIZE_IN_BITS dflags = -1
               | 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 :: DynFlags -> Int
    mAX_SMALL_BITMAP_SIZE dflags
     | wORD_SIZE dflags == 4 = 27
     | otherwise             = 58

    seqBitmap :: Bitmap -> a -> a
    seqBitmap = seqList