In Booth's multiplication algorithm, the multiplier Q is scanned from right to left (LSB to MSB) along with an appended bit Q−1=0.
The operations performed for each pair of adjacent bits (Qi,Qi−1) are:
01: Addition (+M)
10: Subtraction (−M)
00 or 11: No addition or subtraction (only shift)
Given the 16-bit multiplier Q and Q−1=0:
Q=q15q14…q0=1010 0100 1010 1010,Q−1=0 Let us evaluate each bit pair (qi,qi−1) starting from i=0 to 15:
(q0,Q−1)=(0,0)→ No operation
(q1,q0)=(1,0)→ Subtraction
(q2,q1)=(0,1)→ Addition
(q3,q2)=(1,0)→ Subtraction
(q4,q3)=(0,1)→ Addition
(q5,q4)=(1,0)→ Subtraction
(q6,q5)=(0,1)→ Addition
(q7,q6)=(1,0)→ Subtraction
(q8,q7)=(0,1)→ Addition
(q9,q8)=(0,0)→ No operation
(q10,q9)=(1,0)→ Subtraction
(q11,q10)=(0,1)→ Addition
(q12,q11)=(0,0)→ No operation
(q13,q12)=(1,0)→ Subtraction
(q14,q13)=(0,1)→ Addition
(q15,q14)=(1,0)→ Subtraction
Counting all addition and subtraction operations:
Number of subtractions (10 transitions) = 7
Number of additions (01 transitions) = 6
Total number of operations=7+6=13