Official PYQ · 2017Set 1 · Q49Machine Instructions and Addressing ModesNAT1 mark

GATE CS 2017 Set 1 Q49 — Machine Instructions and Addressing Modes

Consider a RISC machine where each instruction is exactly

4

bytes long. Conditional and unconditional branch instructions use PC-relative addressing mode with Offset specified in bytes to the target location of the branch instruction. Further the Offset is always with respect to the address of the next instruction in the program sequence. Consider the following instruction sequence

\begin{array}{ll} \text{Instr. No.} & \text{Instruction} \\ \hline \text{i:} & \text{add R2, R3, R4} \\ \text{i+1:} & \text{sub R5, R6, R7} \\ \text{i+2:} & \text{cmp R1, R9, R10} \\ \text{i+3:} & \text{beq R1, Offset} \\ \end{array}

If the target of the branch instruction is

i,

then the decimal value of the Offset is ____________ .

View worked solution

Answer: -16.0

Let the memory address of the first instruction $i$ be $A$ . Since each instruction is exactly $4$ bytes long, we can determine the addresses of the instructions as follows:

Instruction $i$ : $A$
Instruction $i+1$ : $A + 4$
Instruction $i+2$ : $A + 8$
Instruction $i+3$ (Branch instruction): $A + 12$
Next instruction (after the branch): $A + 16$

According to the problem statement, the branch offset is calculated with respect to the address of the next instruction in the program sequence:

\text{Target Address} = \text{Address of next instruction} + \text{Offset}

We are given that the target of the branch is instruction $i$ (address $A$ ):

A = (A + 16) + \text{Offset}

Solving for the offset:

\text{Offset} = A - (A + 16) = -16

Thus, the decimal value of the Offset is -16.

Free practice · Your answers on this page are not saved.

Published 10 Oct 2026

Report a correction

Browse this topic

More Machine Instructions and Addressing Modes questions

GATE CS 2017 Set 1 Q49 — Machine Instructions and Addressing Modes

Related questions