Question

Find out what the following assembly code calculates AREA my code, CODE EXPORT main ALIGN ENTRY main PROC MOVS MOVS MOVS r0,#0 r1,#15 r2,#0 loop CMP BGT MLA ADDS r2,r1 stop re,r2,r2,ro r2,r2,#1 loop % The final result is saved in register r0 stop B stop ENDP END

Answer 1

Program calculates sum of squares of numbers from 0-15.

• __main: Deals with three registers, r0 to save total sum, r1 to act as loop counter, r2 to save numbers from 0-15
• Loop: loop compares r2 and r1 so that loop executes only till r2 value is less than equal to 15. BGT instruction is executed when this value is greater than 15 and it stops the loop. MLA instruction is used for Multiply-accumulate, its syntax is as below:

MLA         Rd, Rn, Rm, Ra

Rd is destination register

Rn, Rm registers holding the values to be multiplied.

Ra register holding the value to be added.

Thus its equivalent to Rd = (Rn*Rm) + Ra

Heere Rn and Rm both are r2 thus square of the value stored in r2 and adding this value to the sum stored in r0. After this it increments the value in r2 by one and loop executes again for next value calculating square and adding to the sum.

• Stop: End of the program

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