Question

SumMain($a0: &X, $a1: N, $v0: Sum) Write a function to find the sum of the main diagonal elements in a two dimensional N by N array of 32-bit words. The address of the array and the size N are passed to the procedure in registers $a0 and $a1 respectively. The result is returned in $v0. The values in registers $a0 and $a1 should not be modified by this procedure. Calculate the number of clock cycles required to execute your algorithm, assuming N=4.

Answer 1

Solution

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code

       .text
summain:
       lw   $v0, 0($a0)   # first element is 0
       move   $t1, $a0
       addi   $t3, $a1, 1 # computing the offset
       sll   $t3, $t3, 2 # multiply the value by 4
       addi   $t0, $a1, -1 # initializing loop count
       blez   $t0, return
loop:   add   $t1, $t1, $t3   # calculating the next address
       lw   $t2, 0($t1) # t2 equal to Mem(t1)
       add   $v0, $v0, $t2   # adding the value to sum
       addi   $t0, $t0, -1 # decrementing the loop count
       bgtz   $t0, loop
return:   jr   $ra
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