Question

When r0 = 24, r1 = 36 (decimal), how many instructions will the next program fetch? What is r0 when exit the loop?

L1 CMP r0, r1

SUBGT r0, r0, r1

SUBLT r1, r1, r0

BNE L1

Answer 1

Provide the number of instruction the next program will fetch:

Code:

L1: CMP r0, r1 ; Compare the register r0 and r1

SUBGT r0, r0, r1 ; Subtract on Greater than. if r0 > r1 then r0 = r0 - r1.

SUBLT r1, r1, r0   ; Subtract on Less than. if r0 < r1 then r1 = r1 - r0.

BNE L1 ; Branch on not equal to label L1.

• The number of instruction the next program will fetch: 8 instruction

• The value of register r0 on exiting the loop: r0 = 12

Description:

Provided r0 = 24 and r1 = 36

Fetch ⇒ L1: CMP r0, r1 (Compare 24 and 36)

Fetch ⇒ SUBGT r0, r0, r1 (not executed)

Fetch ⇒ SUBLT r1, r1, r0 (r1 = r1 - r0 = 36 - 24 = 12)

Fetch ⇒ BNE L1 (go to label L1)

Fetch ⇒ L1: CMP r0, r1   (Compare 24 and 12)

Fetch ⇒ SUBGT r0, r0, r1 (r0 = r0 - r1 = 24 - 12 = 12)

Fetch ⇒ SUBLT r1, r1, r0   (not executed)

Fetch ⇒ BNE L1 (exit)

• Total number of the fetched instruction: 8

• The value of register r0 after the execution: r0 = 12