An integer arithmetic unit that can perform addition and multiplication of 16-bit un- signed numbers is to be used to multiply two 32-bit unsigned numbers. All operands, intermediate results, and final results are held in 16-bit registers labeled Ro through R15. The hardware multiplier multiplies the contents of R; (multiplicand) by R; (multiplier) and stores the double-length 32-bit product in registers R; and R;+1, with the low-order half in R. When ji-1, the product overwrites both operands. The hardware adder adds the contents of R; and R; and puts the result in Rj. The input carry to an Add operation is 0, and the input carry to an Add-with-carry operation is the contents of a carry flag C. The output carry from the adder is always stored in C. Specify the steps of a procedure for multiplying two 32-bit operands in registers R, Ro, and R3, R2, high-order halves first, leaving the 64-bit product in registers R15, R14, R13, and R12. Any of the registers R through R4 may be used for intermediate values, if necessary. Each step in the procedure can be a multiplication, or an addition, or a register transfer operation.

LO1