Question

just the subquestion iii will be fine

c) The barrel shifter can be used to manipulate signed and unsigned integers without using the multiplication instruction (MULS). Give one simple ARM instruction (not including multiplication) that, when executed, is equivalent to the following mathematical operations: i) Multiply a value in rl by 64 and leave the result in register r2, ii) Multiply a value in r0 by 512 and leave the result in register r4, iii) Multiply a value in r5 by -1 (minus one) and leave the result in r3 .

Answer 1

iii) Multiplying a number with -1 means we are just flipping the sign of that number. If the number is a positive one, the result would be a negative one and if the number is a negative one, the result would be a positive one. The ARM instruction to produce this result is

NEG r3, r5.

The value in the register r5 is reversed and stored in r3 register.

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