// useBitmap.cpp : Implimentation of the CUseBitmap class
//
/////////////////////////////////////////////////////////////////////////////

#include "std.h"
#include "UseBitmap.h"

/////////////////////////////////////////////////////////////////////////
// Find a free bit
//
// Parameters;
// set - true = Free Bit is automatically set if found
//		 false = Bit is not automatically set if found
//
// Returns:
// Number of a free bit (1 to NumOfBits()). A value of
// zero is returned if no free bit can be found
//
UINT32 CUseBitmapGeneral::FindFreeBitGen(const bool set)
{
	// Returned bit number
	UINT32 bit_number = 0;

	// Loop control
	bool stop = false;

	// Word being searched
	UINT32 word = 0;

	// Calculate how many words are defined in bitmap and then search
	// a word at a time
	UINT32 max_word = WordsRequired(length) - 1;

	// Search for a non-full word
	while (!stop && (count < length))
	{
		if (bitmap[word] != ~0)
		{
			// Free bit found. This could be bogus if the last word is padded
			// with blank bits

			// Find free bit in word
			UINT32* p_word = &bitmap[word];	// Pointer to word with free bit

			// Max number of bit defined in this word. This is somewhat less than
			// 32 bits if the free bit resides in the last word and the number of
			// bits defined in the entire bitmask does not reside on a 32 bit
			// boundry
			UINT32 max_bit = (word < max_word) ? 31 : (length-1) % 32;

			UINT32 bit = 0;					// Bit number being examined
			UINT32 bit_mask = 1;			// Mask for examining bit

			do
			{
				if (!((*p_word) & bit_mask))
				{
					// Free bit found
					stop = true;

					// If required, set bit (and keep 'used' count up
					// to date
					if (set)
					{
						*p_word |= bit_mask;
						used++;
					}

					// Calculate true bit number to be returned
					// (Based to 1)
					bit_number = bit + (word << 5) + 1;
				}
				else
				{
					// Check next bit
					if (bit >= max_bit)
					{
						// Free bit was bogus
						stop = true;
					}
					else
					{
						// Step on to next bit
						bit++;
						bit_mask <<= 1;
					}
				}
			} while (!stop);
		}
		else
		{
			if (++word > max_word)
				stop = true;
		}
	}

	return bit_number;
}

// EOF