gistfile1.txt

// iterate newResultsArray in ascending order
// if na[i] == oa[j] and na[i+1] == oa[j+1], assign them to the opposite index+1
// pass 4 is for ascending and 5 descending, block covers logic for both
void (^pass4And5Block)(BOOL, vector<IGListRecord>&, vector<IGListRecord>&) = ^(BOOL ascending, vector<IGListRecord> &newResults, vector<IGListRecord> &oldResults) {
    const NSInteger offset = ascending ? 1 : -1;
    for (NSInteger i = ascending ? 0 : newCount - 1;
         (ascending && i < newCount - 1) || (!ascending && i > 0);
         ascending ? i++ : i--) {

        // don't check block moves for new elements
        if (newResults[i].index == NSNotFound) {
            continue;
        }

        const NSInteger nj = newResults[i].index + offset;
        const NSInteger ni = i + offset;
        const IGListRecord next = newResults[ni];
        const IGListEntry *entry = next.entry;

        // if we are comparing the same entry, it hasn't been updated, and its identity count hasn't changed
        // we can mark the record as part of a block so it isn't counted as an insert/delete
        if (nj < oldCount
            && nj > 0
            && entry == oldResults[nj].entry
            && !entry->updated
            && entry->oldCounter == entry->newCounter) {
            oldResults[nj].index = ni;
            newResults[ni].index = nj;
        }
    }
};

// pass 4
pass4And5Block(YES, newResultsArray, oldResultsArray);

// pass 5
pass4And5Block(NO, newResultsArray, oldResultsArray);