DMIndexSetDivide

void DMIndexSetDivide(NSArray **slices, NSIndexSet *inIndexSet, NSUInteger parts) {
  if (parts == 0 || parts == 1) {
		*slices = [NSArray arrayWithObject:inIndexSet];
		return;
	}
	NSMutableArray *indexSets = [NSMutableArray arrayWithCapacity:parts];
	for (int i = 0; i < parts; i++) {
		indexSets[i] = [NSMutableIndexSet indexSet];
	}
	
	NSUInteger divisor = roundtol(inIndexSet.count / parts);
	__block NSUInteger idx = 0;
	__block NSUInteger indexSetIdx = 0;
	__block NSMutableIndexSet *currentIndexSet = nil;
	[inIndexSet enumerateIndexesUsingBlock:^(NSUInteger index, BOOL *stop) {
		if (idx % divisor == 0) {
			currentIndexSet = indexSets[indexSetIdx];
			if (indexSetIdx + 1 < indexSets.count)
				indexSetIdx++;
		}
		[currentIndexSet addIndex:index];
		idx++;
	}];
	
	*slices = indexSets;
}