# COMP-200: Intro to Computer Systems
## Assignment 3
### mo khan - 3431709

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

Chapter 6:

> 13. 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

```assembly
!include assignments/3/max_min.s
```

<!--
I wrote the following C code and then used the GNU C Compiler to convert the C
code into Assembly code for my machine. Below is the C code, compiler command,
and final assembly code.

main.c
```c
!include assignments/3/main.c
```

bash
```bash
$ gcc -S -fverbose-asm -02 main.c
```

main.s
```assembly
!include assignments/3/main.s
```
-->

Chapter 7:

> 16. 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?
  ```plaintext
    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

  ```plaintext
  | 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`).


  ```plaintext
  | 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.

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

  ```plaintext
  | 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:

```ruby
!include assignments/3/graph.rb
```

Chapter 8:

> 9. 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.

```ruby
!include assignments/3/caesar.rb
```

The plaintext is `MOVE OUT AT DAWN`.

```bash
$ 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:

* https://blog.rchapman.org/posts/Linux_System_Call_Table_for_x86_64/
* https://cs.lmu.edu/~ray/notes/gasexamples/
* https://ftp.gnu.org/old-gnu/Manuals/gas-2.9.1/html_chapter/as_7.html