Write an Assembly language(For MASM): The assignment has two steps. Step1: Write

Question

Write an Assembly language(For MASM):

The assignment has two steps.

Step1: Write an assembly procedure which computes the following:

   int myfib(n)  /* n is a positive integer */

   if (n<=3) return 1;

  /* else */

  return myfib(n-1)+myfib(n-2)+myfib(n-3);

NOTE THAT THE ABOVE FUNCTION IS RECURSIVE. YOUR PROCEDURE NEEDS TO BE RECURSIVE AND COMPUTE EXACTLY AS DESRIBED IN MYFIB(). NO CREDIT WILL BE GIVEN IF YOUR PROCEDURE IS NOT RECURSIVE. NO CREDIT WILL BE GIVEN IF YOUR PROGRAM IS CROSS-ASSEMBLED FROM ANOTHER LANGUAGE.

YOU DECIDE ON WHICH REGISTERS TO USE (FOR PARAMETER PASSING AND RETURNED VALUES, ETC).

Step 2: After completing Step 1, write an assembly program that computes and displays in a separate line the following:

i    myfib(i)

for all integer i, from i=1 to 15.

The initial part of the output will look as the following:

1                     1

2                     1

3                     1

4                     3

5                     5

6                     9

7                     17

. . .

Explanation / Answer

## main--
## Registers used:
## $v0 - syscall parameter and return value.
## $a0 - syscall parameter-- the string to print.
.text
main:
subu $sp, $sp, 32 # Set up main’s stack frame:
sw $ra, 28($sp)
sw $fp, 24($sp)
addu $fp, $sp, 32

## Get n from the user, put into $a0.
li $v0, 5 # load syscall read_int into $v0.
syscall # make the syscall.
move $a0, $v0 # move the number read into $a0.
jal fib # call fib.

move $a0, $v0
li $v0, 1 # load syscall print_int into $v0.
syscall # make the syscall.

la $a0, newline
li $v0, 4
syscall # make the syscall.

li $v0, 10 # 10 is the exit syscall.
syscall # do the syscall.

## fib-- (hacked-up caller-save method)
## Registers used:
## $a0 - initially n.
## $t0 - parameter n.
## $t1 - fib (n - 1).
## $t2 - fib (n - 2).
## $t3-fib(n-3).
.text
fib:
bgt $a0, 1, fib_recurse # if n < 3, then just return a 1,
li $v0, 1 # don’t build a stack frame.
jr $ra
# otherwise, set things up to handle
fib_recurse: # the recursive case:
subu $sp, $sp, 32 # frame size = 32, just because...
sw $ra, 28($sp) # preserve the Return Address.
sw $fp, 24($sp) # preserve the Frame Pointer.
addu $fp, $sp, 32 # move Frame Pointer to new base.

move $t0, $a0 # get n from caller.

# compute fib (n - 1):
sw $t0, 20($sp) # preserve n.
sub $a0, $t0, 1 # compute fib (n - 1)
jal fib
move $t1, $v0 # t1 = fib (n - 1)
lw $t0, 20($sp) # restore n.

# compute fib (n - 2):
sw $t1, 16($sp) # preserve $t1.
sub $a0, $t0, 2 # compute fib (n - 2)
jal fib
move $t2, $v0 # t2 = fib (n - 2)
lw $t1, 16($sp) # restore $t1.
# compute fib (n - 3):
sw $t2, 12($sp) # preserve $t1.
sub $a0, $t0, 3 # compute fib (n - 3)
jal fib
move $t3, $v0 # t3 = fib (n - 3)
lw $t2, 12($sp) # restore $t2.

add $v0, $t1, $t2, $t3 # $v0 = fib (n - 1) + fib (n - 2)+fib(n-3)
lw $ra, 28($sp) # restore Return Address.
lw $fp, 24($sp) # restore Frame Pointer.
addu $sp, $sp, 32 # restore Stack Pointer.
jr $ra # return.

## data for fib-o.asm:
.data
newline: .asciiz " "

## end of fib-o.asm

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