In `G1BlockOffsetTablePart::update_for_block_work`:

```
size_t end_index = _bot->index_for(blk_end - 1);

HeapWord* rem_st = _bot->address_for_index(index + 1);
HeapWord* rem_end = _bot->address_for_index(end_index) + BOTConstants::card_size_in_words();

...

// start == rem_st
// end == rem_end

size_t start_card = _bot->index_for(start);
size_t end_card = _bot->index_for(end-1);
```

It's essentially the following, because `address_for_index` and `index_for` are inverse functions of each other.

```
size_t start_card = index + 1;
size_t end_card = end_index;
```