= Solution
A useful additional mode is \b[base plus <scaled register indexing>], with effective address $B+(I\ll s)$. For an <array> of four-byte elements choose $s=2$, use its base address on the unshifted <ALU> input and its index <processor register> on the <barrel shifter> input, then add. This forms an indexed <machine word> address in one <datapath> pass. An eight-byte element uses $s=3$.
With parallel <ALU> and <barrel shifter> outputs, shifting and adding require either separate instructions/cycles or another route from the <barrel shifter> to the <ALU>. The new serial connection supplies that route. This is an <addressing mode> capability, not a claim that the old instruction encoding already contains the new mode.
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