/*
 * -- we're using some code from the MIT sources
 */
#include "copyright.h"

#define lowbit( x ) ( ( x ) & ( ~( x ) + 1 ) )

/* GetNextBitsOrBreak(bits, mask, base)  -- 
 * (Suggestion: First read the macro, then read this explanation.
 *
 * Either generate the next value to OR in to a pixel or break out of this
 * while loop 
 *
 * This macro is used when we're trying to generate all 2^n combinations of
 * bits in mask.  What we're doing here is counting in binary, except that
 * the bits we use to count may not be contiguous.  This macro will be
 * called 2^n times, returning a different value in bits each time. Then
 * it will cause us to break out of a surrounding loop. (It will always be
 * called from within a while loop.)
 * On call: mask is the value we want to find all the combinations for
 * base has 1 bit set where the least significant bit of mask is set
 *
 * For example,if mask is 01010, base should be 0010 and we count like this:
 * 00010 (see this isn't so hard), 
 *     then we add base to bits and get 0100. (bits & ~mask) is (0100 & 0100) so
 *      we add that to bits getting (0100 + 0100) =
 * 01000 for our next value.
 *      then we add 0010 to get 
 * 01010 and we're done (easy as 1, 2, 3)
 */

#define GetNextBitsOrBreak(bits, mask, base)	\
	    if((bits) == (mask)) 		\
		break;		 		\
	    (bits) += (base);		 	\
	    while((bits) & ~(mask))		\
		(bits) += ((bits) & ~(mask));