The following two signed 2’s complement numbers (multiplicand M and multiplier…

2025

The following two signed 2’s complement numbers (multiplicand M and multiplier Q) are being multiplied using Booth’s algorithm:

M: 1100 1101 1110 1101 and Q: 1010 0100 1010 1010

The total number of addition and subtraction operations to be performed is ___________. (Answer in integer)

Attempted by 93 students.

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Correct answer: 13

Final answer: 13 total operations (6 additions and 7 subtractions).

Reasoning:

  • Booth's algorithm examines pairs (q_i, q_{i-1}) for i = 0..15 after appending q_{-1} = 0. If the pair is 01, add the multiplicand; if 10, subtract the multiplicand; if 00 or 11, do nothing.

  • Write the multiplier bits from LSB to MSB and inspect each pair (q_i, q_{i-1}):

    1. i=0: (0, 0) -> no operation

    2. i=1: (1, 0) -> subtract

    3. i=2: (0, 1) -> add

    4. i=3: (1, 0) -> subtract

    5. i=4: (0, 1) -> add

    6. i=5: (1, 0) -> subtract

    7. i=6: (0, 1) -> add

    8. i=7: (1, 0) -> subtract

    9. i=8: (0, 1) -> add

    10. i=9: (0, 0) -> no operation

    11. i=10: (1, 0) -> subtract

    12. i=11: (0, 1) -> add

    13. i=12: (0, 0) -> no operation

    14. i=13: (1, 0) -> subtract

    15. i=14: (0, 1) -> add

    16. i=15: (1, 0) -> subtract

Count: additions = 6, subtractions = 7, total = 13.

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