You can take Implement factorial using MIPS a look before doing this. This was my college's computer organization assignment. I implemented a Fibonacci using the following algorithm:
In MIPS, I use $a0 as the parameter n of F(n). For example, letting $a0 equal to 10 and jumping to the fib label means F(10), and at the end of the recursion, the result will be stored in $v0.
main:
addi $a0, $zero, 10 # let the parameter n be 10
jal fib # jump to fib label, i.e. calling F(10)
j exit
fib:
addi $sp, $sp, -8 # allocate 8 bytes to this stack
sw $ra, 0($sp) # save the address of the instruction that calls fib label (instruction address)
sw $a0, 4($sp) # save the value of n
slti $t0, $a0, 2 # $t0 is used for conditions. If n < 2 then $t0 = 1, else $t0 = 0
beq $t0, $zero, L1 # if $t0 == 0 then jump to branch L1
add $v0, $v0, $a0 # let $v0 add n
addi $sp, $sp, 8 # let $sp point to upper stack
jr $ra # jump to the next line of the line calling fib
L1:
addi $a0, $a0, -1 # n = n - 1
jal fib # jump to fib label again, like as calling F(n - 1)
addi $a0, $a0, -1 # n = n - 1
jal fib # jump to fib label again, like as calling F(n - 2)
lw $a0, 4($sp) # recover the value of n
lw $ra, 0($sp) # recover instruction address
addi, $sp, $sp, 8 # let $sp point to upper stack
jr $ra # jump to the next line of the line calling L1
exit:
The execution result of the MARS simulator looks like this:
You can see that the value of $v0 is 0x37, 55 in decimal, which is the result of F(10).
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