GATE CSE 2000 | Question: 1.10

Question

The most appropriate matching for the following pairs$$\begin{array}{ll} \text{X: Indirect addressing} & \text{1: Loops } \\  \text{Y: Immediate addressing } & \text{2: Pointers} \\   \text{Z: Auto decrement addressing } & \text{3: Constants } \\  \end{array}$$ is

• A. $X - 3,  Y - 2,  Z - 1$
• B. $X - 1,  Y - 3,  Z - 2$
• C. $X - 2,  Y - 3,  Z - 1$
• D. $X - 3,  Y - 1,  Z - 2$

Comments

Register add mode :  access the local variables

Immediate add mode : access the  constant

Direct/Absolute add mode : access the static variables

Indirect add mode : implement pointer

indexed/ Base index : access the random array

Auto index: access the linear array

relative add mode and base register add mode : relocation at run time

base register add mode : best suit to write positions independent code

---

base register add mode : best suit to write positions independent code

@mohan123

Why not PC relative add mode is best suit ?

---

@Satbir

positions independent code means we can transfer control of statement  multiple segment  using diff diff base address 

but pc relative control will be transfer  within the  segment  

---

indirect addressing mode  ---  pointer

immididate mode            ----- constant access     

 auto incremented addressing in form of loops

 

Answer 1

(C) is the most appropriate one.

General instruction format: |opcode|Mode|Address Field|
Pointer dereference $\rightarrow $ Indirect addressing, $E.A = M$ [Value stored in address field]
Operating with a constant $\rightarrow $ Immediate addressing, $E.A =$ Address field of the instruction.
Loop iteration counter check $\rightarrow $ Auto decrement addressing $R1=R1-1$; $E.A = R1$

E.A = Effective address, where the required operand will be found.

Comments

Pointer dereference-> indirect addressing
Operating with a constant -> immediate addressing
Loop iteration counter check -> auto decrement addressing

---

Please explain autodecrement addressing and loops

---

@barney ross

for(i=n; i<1000; )        // loop

{   i=i-1

}

Answer 2

Indirect addressing:
Indirect addressing means that the address of the data is held in an intermediate location so that the address is first 'looked up' and then used to locate the data itself.

Immediate addressing:
Immediate Addressing. An immediate operand has a constant value or an expression. When an instruction with two operands uses immediate addressing, the first operand may be a register or memory location, and the second operand is an immediate constant.

 Auto increment or decrements: can be one by using loops.

Answer 3

Indirect Addressing Mode is used in case of Pointers (to hold address of operands).

Immediate Addressing Mode is used to initialize registers with constant value.

Auto-decrement Addressing Mode implements Loops to automatically decrement the contents of the register specified in the instruction, which is used as the effective address of the operand.

Therefore, Option C is correct.

Answer 4

• X → 2 (Pointers)
  Indirect addressing  Effective address=M[A]
• Y → 3 (Constants)
  Immediate addressing the address field of the instruction contains the operand 
• Z → 1 (Loops)
  Auto-decrement  -(R)  is useful in loops  $1$. Decrement R by operand size   $2.$ E[A] = [R] = Content of R