Question

Consider the following assembly language program for a hypothetical processor. A, B and C are 8 bit registers. The meanings of various instructions are shown as comments.

MOV B, #0 ; B $\leftarrow$ 0

MOV C, #8 ; C $\leftarrow$ 8

Z : CMP C, #0 ; Compare C with 0

JZ X ; Jump to X if 0 flag is set

SUB C, #1 ; C $\leftarrow$ C - 1

RRC A, #1 ; Rotate right A through carry by one bit

JC Y ; Jump to Y if any carry flag is set

JMP Z ; Jump to Z

Y : ADD B, #1 ; B $\leftarrow$ B + 1

JMP Z ; Jump to Z

X :

If the initial value of register A is $A_0$ the value of register B after the program execution will be

• A. $A_0$
• B. the number of 0 bits in $A_0$
• C. 8
• D. the number of 1 bits in $A_0$

Answer 1

The correct option is D the number of 1 bits in $A_0$

$A\leftarrow A_0$

The value of B after execution of the program is number of 1 bits in $A_0$