Goals for the Lab: We build up on prior labs and explore basics of functions and recursion.
Background:
- Calling a subroutine is between a caller, who makes the subroutine call, and the callee, which is the subroutine itself.
- The caller passes arguments to the callee by placing the values into the argument registers $a0-$a3.
- The caller calls jal followed by the label of the subroutine. This saves the return address in $ra. The return address is PC + 4, where PC is the address of the jal instruction. If the callee uses a frame pointer, then it usually sets it to the stack pointer. The old frame pointer must be saved on the stack before this happens.
- The callee usually starts by pushing any registers it needs to save on the stack. If the callee calls a helper subroutine, then it must push $ra on the stack. It may need to push temporary ($t0-$t7) or saved registers ($s0-$s7) as well.
- Once the subroutine is complete, the return value is placed in $v0-$v1.The callee then calls jr $ra to return back to the caller.
Exercise 1 – With Sample Code: Study the code given below.
Exercise 2: Write a function to count the number of vowels in a given string and also return the string after removing the vowels and print that string in main function. Call the function twice with two different strings.
Input : String (without space)
Output : Single integer
Exercise 3: Write a program that asks if the user wants a triangle or a square. It then asks the user for the size of the object (the number of lines it takes to draw the object). The program then writes a triangle or a square of stars “*” to the console.
*******
*******
*******
*******
*******
*******
or
*
**
***
****
***** ******
Write a subroutine for each figure. In them, use a subroutine print_star_line that writes a line of a given number of stars. (that number is passed as an argument to print_star_line function).
Take home assignment:
Print the pyramid as:
*
**
***
****
*****
******
*******
Exercise 4: Find Factorial of a given integer recursively. Take care of the base case.
Exercise 5: Disassemble the following hex instructions.
- 02002009
- 03e00008
- 0c100013
References: http://stackoverflow.com/questions/18991655/how–do–you–perform–a–recursive–operation–inmips–assembly
http://stackoverflow.com/questions/22317560/mips–assembly–removing–vowels–from–aninput–string
