| BitHelper |
ABOUT: Helps with operations that rely on bit marking to indicate whether an item in the collection should be added, removed, visited already, etc. BitHelper doesn't allocate the array; you must pass in an array or ints allocated on the stack or heap. ToIntArrayLength() tells you the int array size you must allocate. USAGE: Suppose you need to represent a bit array of length (i.e. logical bit array length) BIT_ARRAY_LENGTH. Then this is the suggested way to instantiate BitHelper: *************************************************************************** int intArrayLength = BitHelper.ToIntArrayLength(BIT_ARRAY_LENGTH); BitHelper bitHelper; if (intArrayLength less than stack alloc threshold) int* m_arrayPtr = stackalloc int[intArrayLength]; bitHelper = new BitHelper(m_arrayPtr, intArrayLength); else int[] m_arrayPtr = new int[intArrayLength]; bitHelper = new BitHelper(m_arrayPtr, intArrayLength); *************************************************************************** IMPORTANT: The second ctor args, length, should be specified as the length of the int array, not the logical bit array. Because length is used for bounds checking into the int array, it's especially important to get this correct for the stackalloc version. See the code samples above; this is the value gotten from ToIntArrayLength(). The length ctor argument is the only exception; for other methods -- MarkBit and IsMarked -- pass in values as indices into the logical bit array, and it will be mapped to the position within the array of ints. FUTURE OPTIMIZATIONS: A method such as FindFirstMarked/Unmarked Bit would be useful for callers that operate on a bit array and then need to loop over it. In particular, if it avoided visiting every bit, it would allow good perf improvements when the bit array is sparse. |