code: func (idx *MemoryIndex) FindCRC32(h plumbing.Hash) (uint32, error) {
  	k := idx.FanoutMapping[h[0]]
  	i, ok := idx.findHashIndex(h)
  	if !ok {
  		return 0, plumbing.ErrObjectNotFound
  	}
  
  	return idx.getCRC32(k, i), nil
  }
docs: // FindCRC32 implements the Index interface.