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COMP-200: Intro to Computer Systems

Assignment 3

mo khan - 3431709

Choose ONE exercise each from Chapters 6, 7, and 8

Chapter 6:

  1. Write a complete assembly language program (including all necessary pseudo-ops) that reads in a series of integers, one at a time, and outputs the largest and smallest values. The input will consist of a list of integer values
!include assignments/3/max_min.s

Chapter 7:

  1. Given the following diagram, where the numbers represent the time delays across a link:

a. How many simple paths (those that do not repeat a node) are there from node A to G?

  A<->B: 5
  A<->D: 6
  A<->F: 3
  B<->C: 4
  B<->E: 2
  C<->D: 3
  C<->E: 1
  C<->G: 2
  D<->E: 1
  F<->G: 8

There are 7 simple paths

| Path        |
| ----        |
| a,b,c,g     |
| a,b,e,c,g   |
| a,b,e,d,c,g |
| a,d,c,g     |
| a,d,e,b,c,g |
| a,d,e,c,g   |
| a,f,g       |

b. What is the shortest path from node A to node G? What is the overall delay?

The shortest path has a distance of 10. The overall delay is 11 (((11 + 10 + 13 + 11 + 15 + 10 + 11)/7) = 11).

| Path        | Total Distance |
| ----        | -------------- |
| a,b,c,g     | 5+4+2 = 11     |
| a,b,e,c,g   | 5+2+1+2 = 10   |
| a,b,e,d,c,g | 5+2+1+3+2 = 13 |
| a,d,c,g     | 6+3+2 = 11     |
| a,d,e,b,c,g | 6+1+2+4+2 = 15 |
| a,d,e,c,g   | 6+1+1+2 = 10   |
| a,f,g       | 3+8 = 11       |

c. If node E fails, does that change the shortest path? If so, what is the new shortest path?

Yes, if node E fails then there are 3 simple paths remaining with the shortest path having a distance of 11.

  A<->B: 5
  A<->D: 6
  A<->F: 3
  B<->C: 4
  C<->D: 3
  C<->G: 2
  F<->G: 8

| Path        | Total Distance |
| ----        | -------------- |
| a,b,c,g     | 5+4+2 = 11     |
| a,d,c,g     | 6+3+2 = 11     |
| a,f,g       | 3+8 = 11       |

The following code can be used to prove these results:

!include assignments/3/graph.rb

Chapter 8:

  1. Using a Caesar cipher with s = 5, decode the received message RTAJ TZY FY IF

The following code can be used to decipher the Caesar cipher.

!include assignments/3/caesar.rb

The plaintext is MOVE OUT AT DAWN.

$ ruby caesar.rb
# Caesar Cipher

| --------------- | --------------------------------------------------- |
| Plain Alphabet  | A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z |
| Cipher Alphabet | F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,A,B,C,D,E |
| --------------- | --------------------------------------------------- |
| Key             | 5                                                   |
| Ciphertext      | RTAJ TZY FY IFBS                                    |
| Plaintext       | MOVE OUT AT DAWN                                    |

References: