Question

1) Provide the type and assembly language instruction for the following binary value: 0000 0010 0001 0000 1000 0000 0010 0000 (two)

2) Provide the type, assembly language instruction, and binary representation of instruction described by the following MIPS fields: op=0, rs=3, rt=2, rd=3, shamt=0, funct=34

3)For the following C statement, write a minimal sequence of MIPS assembly instructions that does the identical operation. Assume $t1 = A, $t2 = B, and $s1 is the base address of C. A = C[0] << 4;

4) Consider the following MIPS loop:

LOOP: slt $t2, $0, $t1

beq $t2, $0, DONE

subi $t1, $t1, 1

addi $s2, $s2, 2

j LOOP

DONE:

4a) Assume that the register $t1 is initialized to the value 10. What is the value in register $s2 assuming $s2 is initially zero?

4b) For each of the loops above, write the equivalent C code routine. Assume that the registers $s1, $s2, $t1, and $t2 are integers A, B, i, and temp, respectively.

4c) For the loops written in MIPS assembly above, assume that the register $t1 is initialized to the value N. How many MIPS instructions are executed?

Answer 1

1) Provide the type and assembly language instruction for the following binary value:
0000 0010 0001 0000 1000 0000 0010 0000 (two)
Answer:----------

000000	10000	10000	10000	00000	100000
Op=0	rs = 16	rt = 16	rd = 16	shamt=0	funct =0x20
(add)	($s0)	($s0)	($s0)		(add)

Thus this is a R-type instruction: add $s0,$s0,$s0

2) Provide the type, assembly language instruction, and binary representation of instruction described by the following MIPS fields: op=0, rs=3, rt=2, rd=3, shamt=0, funct=34
Answer:----

000000	00011	00010	00011	00000	100010
Op=0	rs = 3	rt = 2	rd = 3	shamt=0	funct =34
	($v1)	($v0)	($v1)		(sub)

So,
Type of instruction:--------- R-type instruction
Assembly language instruction :----------- sub $v1, $v0 , $v1

3)For the following C statement, write a minimal sequence of MIPS assembly instructions that does the identical operation. Assume $t1 = A, $t2 = B, and $s1 is the base address of C. A = C[0] << 4;
Answer:----
Assume the base address of C is in $s1 and that A is in $s2. Use the minimum number of registers. Do not destroy   the contents of $s1 or $s2.  
A   =   C[0]   <<   4;  
lw $t1,   0($s1) ---------------------- # loads C[0] into A  
sll $t1 ,$t1, 4 --------------------------# shift left by 4 bits contents of $t1  
sw $t1,   0($s2) --------------------- #  store C[0] << 4 into A  

4) Consider the following MIPS loop:

LOOP: slt $t2, $0, $t1

beq $t2, $0, DONE

subi $t1, $t1, 1

addi $s2, $s2, 2

j LOOP

DONE:

4a) Assume that the register $t1 is initialized to the value 10. What is the value in register $s2 assuming $s2 is initially zero?
Answer:----
LOOP:
slt $t2, $0, $t1 ------------------------- # if $t1 > 0 then $t2 = 1 else $t2 = 0
beq $t2, $0, DONE ------------------- # if $t2 = 0 then go to DONE
subi $t1, $t1, 1-------------------------- # $t1 = $t1 -1
addi $s2, $s2, 2 ------------------------- # $s2 = $s2 + 2
j LOOP --------------------------- # Go to LOOP
DONE:

Number of loop executions:
$t1 at top = 10;
$t1 at bottom = 9
...............…
t1 at top = 1; $t1 at bocom = 0 => 10 executions => s2 = 2x10 = 20

4b) For each of the loops above, write the equivalent C code routine. Assume that the registers $s1, $s2, $t1, and $t2 are integers A, B, i, and temp, respectively.
Answer:----
while(i > 0){
i= i // Decrement i by one during each iteration of the loop (sub $t1, $t1, 1)
B = B + 2 // Increment B by 2 each time (addi $s2, $s2, 2)
} //exit loop

4c) For the loops written in MIPS assembly above, assume that the register $t1 is initialized to the value N. How many MIPS instructions are executed?
Answer:----
Base case: N= 0. If N=0, only 2 MIPS instructions are executed:

LOOP: slt $t2, $0, $t1 -------------------------- # 0 == 0; here, $t2 = 0 [#1]
beq $t2, $0, DONE ------------------------------ # 0 == 0; go to DONE [#2]
sub $t1, $t1, 1
addi $s2, $s2, 2
j LOOP
DONE:
For any value of N > 0, (N full loops + 2 lines) of MIPS instructions must be executed; each full loop contains 5 MIPS instructions. Therefore, if the register $t1 is initialized to the value N, a total of (5*N)+2 MIPS instructions are executed.