Nested_Procedures

#### Stack Push
- Putting values ON the stack. Using FIFO data structure, thus can place onto the top of the stack.
- $sp register - ptr to memory address, FIFO
- Steps:
	- Reserve space on the stack by decrementing x (needed) bytes
		- store values on the stack using store word procedure ``sw`` into a register (i.e. ``$a#``) using the stack pointer ``$sp``

 2 ints = 4 bytes x 2 = 8 bytes needed, split accordingly (0 - 3, 4 - 7)
```
addiu $sp, $sp, -8 # -> reserve the top 8 bytes on stack
```
 Now, to actually store the 2 integers (in $a0 and $a1), use store word procedure
```
sw $a0, 0($sp) # store integer 1 @ bytes 0-3 , above stack ptr
sw $a1, 4($sp) # store integer 2 @ bytes 4-7, above stack ptr
```
#### Stack Pop
- Reverse of stack push 
- Steps:
	- Copy value from stack into register, i.e. ``$a#`` 
	- de-allocate the x bytes used on the stack using load word procedure ``lw`` 
Ex: Retrieve the 2 ints off the stack
```
lw $a0, 0($sp) # load the first int @ bytes 0 - 3
lw $a1, 4($sp) # load the second int @ bytes 4 - 7
```
Then, de-allocate the space
```
addiu $sp, $sp, 8 # de-allocate the 8 bytes on the stack ptr