created 06/29/2003; revised 06/30/2015

Chapter 21 Programming Exercises

For these programming exercises, use only those instructions that have been discussed so far in these notes:

Basic Instructions
add div mflo slt, slti
addi divu mult sltu, sltiu
addiu j multu sra
addu lb nor srl
and lbu or sub
andi lh ori subu
beq lhu sb sw
bgez lui sh xor
bltz lw sll xori
bne mfhi    
la lw nop  
li move sw  

In the Settings menu of SPIM set Bare Machine OFF, Allow Pseudo Instructions ON, Load Trap File OFF, Delayed Branches ON, Delayed Loads ON, Mapped IO OFF, Quiet OFF.

In these programs do not set up a base register as has been done in previous chapters. Use the lw and sw instructions with symbolic addresses. Use mnemonic register names in your programs and use registers in their conventional ways.

*Exercise 1 — Horner's Method

(see Exercise 4 of chapter 15)

Evaluate the following polynomial using Horner's method:

ax3 + bx2 + cx + d

Now the values for the coefficients a, b, c, d as well as for x come from the .data section of memory:

x:      .word    7
a:      .word   -3
bb:     .word    3
c:      .word    9
d:      .word  -24
result: .word    0

Use the pseudoinstruction lw to get the coefficients from memory, and sw to write the result back to memory.

(Recall that the symbolic address b cannot be used in SPIM.)

Click here to go back to the main menu.

*Exercise 2 — Pair-wise Addition

Declare three arrays, each of the same size:

size     .word       7
array1:  .word     -30, -23, 56, -43, 72, -18, 71
array2:  .word      45,  23, 21, -23, -82,  0, 69
result:  .word       0,   0,  0,   0,   0,  0,  0

Initialize a base register for each array (use the la instruction.) Now implement a loop that adds corresponding elements in the first two arrays and stores the result in the corresponding element of the result array. Do this by moving each of the three base registers to its next array element after each addition.

Click here to go back to the main menu.

***Exercise 3 — String Comparison

Declare two null-terminated strings:

result:  .word     0
string1: .asciiz   "puffin"
string2: .asciiz   "puffins"

Initialize a base register for each string (use the la instruction.) Write a program that sets result to 1 if the two strings are equal and to 0 if the strings are not equal.

Two strings are equal if they are the same length and contain the same character in each location. Otherwise the strings are not equal.

Test your program for a variety of strings. You will have to edit the data section of your program for each pair of strings tested.

Extra: write the program so that it does case insensitive string comparison. Here, two strings are equal if they are the same length and have the same letter (disregarding case) in each location.

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End of Exercises