Question

Question 1. Assume the following C program and You are writing code using SPIM to implement this program.

int a [4], b[4], dot-prod, i; .............. dot_prod = 0; for (i=0; i<4; i++) dot_prod += a[i]*b[i];

Write the results of each of the following in MIPS instructions. Use registers $t0 - $t7 as needed, Note: int requires 8 bytes

1. Load the contents of dot_prod and i into registers
2. Load the contents of a[i] and b[i] into registers
3. Calculate dot_prod + a[i]*b[i] and save the result into dot_prod

please answer each point from (1,2,3) in separated like this :
1.
2.
3.
to help me to understand

Answer 1

Please up vote ,comment if any query i will answer , Thanks.

Note : check attached image for output ,Code compiled and tested in MARS simulator MIPS.

Note : in Answer label i answered all your 1,2,3 questions.

Program Plan :

1. load address of dot_prod and i variable in register and from register get its value.
2. load address of array A and B into registers
3. run a loop in loop label using branch instruction where till i less than 4
4. multiply a[i] and b[i] and multiply add into dot_prod value
5. after loop store dot_prod value into its RAM location and print value.

Program ;

.data
   a: .word 5,6,7,8 #array A
   b: .word 4,3,2,1 #array B
   dot_prod : .word 0 #int variable dot_prod
   i: .word 0 #int variable i
.text
   .globl main
   main:
       la $t0,dot_prod #load address of dot_prod in $t0
       lw $t7,($t0) #load value at address stored in $t0
       la $t1,i #load address of i in $t1
       lw $t1,($t1) #load value at address stored in $t1 and store value in $t1(to reduce register usage)
       la $t2,a #load address of Array A in $t2
       la $t3,b #load address of Array B in $t3
  
   loop:
       #branch to exit if $t1 equal to 4
       beq $t1,4,exit   
       lw $t4,($t2) #load int value (word) from location store in $t2 iton $t4
       lw $t5,($t3) #load int value (word) from location store in $t3 into $t5
      
       mul $t6,$t4,$t5 #$t6= a[i]*b[i]
       add $t7,$t7,$t6 #$t7=$t7+$t6
      
       addi $t2,$t2,4 #go to next location array A
       addi $t3,$t3,4 #go to next location array B
       addi $t1,$t1,1 #increment i i=i+1
       #jump to loop label
       j loop
   exit:
       #store dot_prod at its location stored in $t0
       sw $t7,($t0)
      
       #again load address of dot_prod in $t1
       la $t1,dot_prod
       #load value from address of dot_prod store in $t1
       lw $t2,($t1)
      
       #print value of dot_prod
      
       li $v0,1
       #move $t2 value into $a0 to print dot_prod value
       move $a0,$t2
       syscall
       #terminate program
       li $v0,10
       syscall
      
Answer :

1. Load the content of dot_prod and i into registers

la $t0,dot_prod #load address of dot_prod in $t0
       lw $t7,($t0) #load value from  address stored in $t0
       la $t1,i #load address of i in $t1
       lw $t1,($t1) #load value from  address stored in $t1 and store value in $t1(to reduce register usage)

2.  Load the contents of a[i] and b[i] into registers

loop:

#$t2 have location of Array A

#$t4 have content of a[i] $t4=a[i]

#$t3 have location of Array B

#$t5 have content of $t5=b[i]

       lw $t4,($t2) #load int value (word) from location store in $t2 into $t4
       lw $t5,($t3) #load int value (word) from location store in $t3 into $t5
      
#go to next index value by adding 4 to its address

#word in MIPS takes 4 bytes so add 4

  
           addi $t2,$t2,4 #go to next location array A
       addi $t3,$t3,4 #go to next location array B

3. Calculate dot_prod + a[i]*b[i] and save the result into dot_prod

#mul multiply a[i]*b[i ] and store into $t6

#add instruction add $t7 and $t6 and store it into $t7

#$t7 have value of dot_prod variable

mul $t6,$t4,$t5 #$t6= a[i]*b[i]
       add $t7,$t7,$t6 #$t7=$t7+$t6
      
#now store value into dot_prod variable RAM location

#$t0 have address of dot_prod and sw store $t7 value into location at store in $t0

#store dot_prod at its location stored in $t0
       sw $t7,($t0)

Output :

Mars Messages Run 110 Clear |-- program is finished running --

Please up vote .comment if any query . Thanks.