1. MIPS Assembly Language Programming
CDA 3101 Discussion Section 06
MIPS Assembly Language Programming
Function Call and Recursive

2. Problem1 Write a function MinMax(&X, N) to find the minimum and
maximum of an array X of N integers. The address of the
array is passed in $a0, and the number of words in the array
is passed in $a1. The minimum and maximum are returned in
registers $v0 and $v1 respectively.
Also, write a short main program that
Prompts user to enter 10 integers one by one to fill a global integer array X of size 10
Calls the MinMax function to find and return the minimum and maximum of the array X.
Prints the minimum and the maximum value.

3. System Calls

4. Problem 2
Implement a recursive function that determines if a string is palindrome. The function should return 1 or 0 to the calling function to indicate if the given string is palindrome or not. You can assume that the string has only characters from the set {a-z, A-Z}. Note that:
palindrome(X) = true, if |X| < 2
palindrome(aXa) = palindrome(X), if |X| >= 2

5. Conventions for Registers
Following registers should be spilled to the stack
$ra ($31)
$a0-$a3 ($4-$7)
$t0-$t7 ($8-$15)
$s0-$s7 ($16-$23)
$fp ($30)
Saved by caller on stack before jal and restored after returning from jal; done only for registers used after jal
Saved by called procedure before rewriting and then restored back before returning

6. Conventions for Function Call
Before calling a function, the caller must
Save on stack
$ra
any $t registers that will be used after the jal instruction
Any $a registers that will be used after the jal instruction
Move arguments to $a0-$a3
Execute jal instruction to jump to the procedure

7. Conventions for Function Call
On entry, the called function must
Save on stack
any $s registers that it is going to overwrite
Before returning, the called function must
Save results in $v0-$v1
Restore all $s registers values from the stack if necessary
Adjust $sp to point to the address it was pointing to before this function was called
Return to calling function by using jr $ra

8. Conventions for Function Call
After the function returns, the caller must
Read the results returned by the function from $v0-$v1
Restore $ra register values from stack
Restore $t and $a register values from stack, if their values were saved on stack before function call

9. Key Points Dynamically allocate memory
li $v0, 9 # Memory allocation service
li $a0, <int> # Allocate <int> bytes of mem.
syscall
move $t0, $v0 # Move address of array to safety.
Recursion
self: …
addi $sp, $sp, -4 # Allocate stack space
sw $ra, 0($sp) # Save old return address
jal self # Jump to self
lw $ra, 0($sp) # Load old return address
addi $sp, $sp, 4 # Restore stack to old state