NSIndexSet category to get the nth index in the index set. (0 based position)

gistfile1.txt

@interface NSIndexSet (NthPosition)
- (NSUInteger)indexAtIndex_ppb:(NSUInteger)position;
@end

@implementation NSIndexSet (NthPosition)
- (NSUInteger)indexAtIndex_ppb:(NSUInteger)position {
  __block NSUInteger index = NSNotFound;
  if (position < self.count) {
    __block NSUInteger count = 0;
    [self enumerateRangesUsingBlock:^(NSRange range, BOOL *stop) {
      if ((count + range.length) > position) {
        index = range.location + (position - count);
      }
      
      count += range.location;
      *stop = count > position;
    }];
  }
  return index;
}

@end

Any feedback is welcome :)