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Arizona State UniversityCSE 420CSE420-Module 1- Soultions

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CSE 420: Computer Architecture 1 Module 1 Sample Questions Question 1 (15 points) (10 mins) [MIPS Assembly Language Programming] Write MIPS assembly language program for the AddOddElement routine s ... hown below. This routine sums only the odd elements of an array. You should write a recursive function, similar to the one below. Stick to MIPS calling and register conventions as much as possible. Hint: You can check your solution by trying it out on MARS. int AddOddElement( int arr[], int size ) { if ( size == 0 ) return 0 ; else if ( arr[ size - 1 ] % 2 == 1 ) return AddOddElement( arr, size - 1 ) + arr[ size - 1 ] ; else return AddOddElement( arr, size - 1 ) ; } Answer: Usually, the hard part is to decide what registers to save. arr is stored in $a0, and that this value really doesn't change throughout. size may need to be saved, though size - 1 appears to be more useful. Since we make calls to AddOddElement, we need to save $ra. So, let's save size - 1 and $ra to the stack. It turns out we also need to save arr[ size - 1 ] to the stack too. AddOddElement: addi $sp, $sp, -12 # Adjust sp addi $t0, $a0, -1 # Compute size - 1 sw $t0, 0($sp) # Save size - 1 to stack sw $ra, 4($sp) # Save return address bne $a0, $zero, CASE1 # branch !( size == 0 ) li $v0, 0 # Set return value to 0 addi $sp, $sp, 12 # Adjust sp jr $ra # Return CASE1: li $t7, 4 # t7 = 4 multi $t0, t7 # Multiple size - 1 by 4 mflo $t1 # Put result in t1 add $t1, $t1, $a0 # Compute & arr[ size - 1 ] lw $t2, 0($t1) # t2 = arr[ size - 1 ] andi $t3, $t2, 1 # is arr[ size - 1 ] odd beq $t3, $zero, CASE2 # branch if even sw $t2, 8($sp) # save arr[ size - 1 ] on stack move $a1, $t0 # update second arg jal AddOddElement lw $t2, 8($sp) # restore arr[ size - 1 ] from stack add $v0, $v0, $t2 # update return valuelw $ra, 4($sp) # restore return address from stack addi $sp, $sp, 12 # Adjust sp jr $ra # Return [Show More]

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