# File lib/grit/git-ruby/internal/pack.rb, line 121
        def init_pack
          with_idx do |idx|
            @offsets = [0]
            FanOutCount.times do |i|
              pos = idx[i * IdxOffsetSize,IdxOffsetSize].unpack('N')[0]
              if pos < @offsets[i]
                raise PackFormatError, "pack #@name has discontinuous index #{i}"
              end
              @offsets << pos
            end
            @size = @offsets[-1]
          end
        end