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BitMap.c
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2006-04-27
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code BitMap
-- Harry Porter -- September 18, 2004
behavior BitMap
method Init (numberOfBits: int)
-- Initialize the BitMap instance, including the allocation of
-- an array of words to hold the data. The computation of
-- numberOfWords is such that there will always be enough room
-- for one extra bit. This is so that there will always be at
-- least one clear ("0") bit just beyond the bits holding the
-- data. This is so the "FindAndSet" method can use a faster
-- algorithm.
--
-- NOTE: This routine calls "alloc".
--
var numWords: int = (numberOfBits / 32) + 1
if numberOfBits <= 0
FatalError ("In BitMap.Init, the numberOfBits is zero or less")
endIf
numBits = numberOfBits
arrayOfWords = alloc array of int { numWords of 0 }
endMethod
method Print ()
-- Print the bit vector showing (by number) which bits have
-- been set. For example:
-- BitMap with the following bits set: 0 1 2 7 9 13 99
--
var i: int
print ("BitMap with the following bits set:")
for i = 0 to numBits-1
if self.IsBitSet (i)
print (" ")
printInt (i)
endIf
endFor
nl ()
endMethod
method Print2 ()
-- Print the bit vector showing each bit as "0" or "1". Spaces are
-- inserted after every 8 bits for readability. For example:
-- BitMap: 11100101 00110110 11011
--
var i: int
print ("BitMap:")
for i = 0 to numBits-1
if i%8 == 0
print (" ")
endIf
if self.IsBitSet (i)
print ("1")
else
print ("0")
endIf
endFor
nl()
endMethod
method NumberOfClearBits () returns int
-- This method returns the number of bits that are clear (i.e., "0").
var i, count: int
count = 0
for i = 0 to numBits-1
if !self.IsBitSet (i)
count = count + 1
endIf
endFor
return count
endMethod
method SetBit (bitNum: int)
-- This method is passed the number of a bit; it sets the bit to "1".
-- Bits are indexed with numbers from 0 through numberOfBits-1.
var word: int
if (bitNum < 0) || (bitNum >= numBits)
FatalError ("Within BitMap.SetBit: invalid bitNum")
endIf
word = bitNum / 32
arrayOfWords [word] = (arrayOfWords [word]) | (0x00000001 << bitNum % 32)
endMethod
method ClearBit (bitNum: int)
-- This method is passed the number of a bit; it clears the bit to "0".
-- Bits are indexed with numbers from 0 through numberOfBits-1.
var word: int
if (bitNum < 0) || (bitNum >= numBits)
FatalError ("Within BitMap.ClearBit: invalid bitNum")
endIf
word = bitNum / 32
arrayOfWords [word] = (arrayOfWords [word]) & ! (0x00000001 << bitNum % 32)
endMethod
method IsBitSet (bitNum: int) returns bool
-- This method is passed the number of a bit; it returns TRUE iff that bit is
-- set to "1". Bits are indexed with numbers from 0 through numberOfBits-1.
var word: int
if (bitNum < 0) || (bitNum >= numBits)
FatalError ("Within BitMap.IsBitSet: invalid bitNum")
endIf
word = bitNum / 32
return (((arrayOfWords [word]) >> (bitNum % 32)) & 0x00000001) != 0
endMethod
method FindZeroAndSet () returns int
-- This method finds the first bit that is clear (i.e., "0"). The sets
-- it to "1" and returns index of the bit. If all bits are already set,
-- this method returns -1.
--
-- Note: The arrayOfWords was initialized so that there is always at least
-- one extra bit beyond the end, which will be zero. This allows the
-- search for a clear bit to use a faster algorithm, which finds the
-- first clear bit, then tests to see if it is a legal bit.
--
var i, word: int
-- Find the first word containing at least one clear bit.
while arrayOfWords [i] == 0xffffffff
i = i + 1
endWhile
-- Find the clear bit within that word.
word = arrayOfWords [i]
i = i * 32
while (word & 0x00000001) != 0
i = i + 1
word = word >> 1
endWhile
-- See if this is a legal bit; if so set the bit and return its index.
if i >= numBits
return -1
else
self.SetBit (i)
return i
endIf
endMethod
endBehavior
-- This function is used to test/debug the BitMap code.
function TestBitMap ()
var bm: BitMap = new BitMap
i, j: int
print ("Running test of 'BitMap' class....\n")
bm.Init (40)
bm.Print2 ()
for i = 0 to 40
print ("Calling FindZeroAndSet(") printInt (i) print (")...")
j = bm.FindZeroAndSet ()
print (" returns... ")
printInt (j)
nl ()
bm.Print2 ()
endFor
print ("Clear each of the bits...\n")
for i = 0 to 39
bm.ClearBit (i)
bm.Print2 ()
endFor
print ("number clear = ") printInt (bm.NumberOfClearBits ()) nl ()
print ("Set each of the bits...\n")
for i = 0 to 39
bm.SetBit (i)
bm.Print2 ()
print ("number clear = ") printInt (bm.NumberOfClearBits ()) nl ()
endFor
bm.ClearBit (3)
bm.ClearBit (4)
bm.ClearBit (5)
bm.ClearBit (6)
bm.ClearBit (32)
bm.Print2 ()
bm.Print ()
endFunction
endCode