Assignment 2, due Jan 30

On every assignment, write your name legibly as it appears on your University ID card! Homework is due on paper at the start of class on the day indicated (usually Friday). Exceptions will be made only by advance arrangement (excepting "acts of God"). Late work must be turned in to the TA's mailbox (ask the CS receptionist in 14 MLH for help). Never push homework under someone's door!

1. A problem: Convert the following decimal numbers to unsigned 8-bit binary numbers: (0.1 points each)

   a) 100 = 01100100
   b) 120 = 01111000
   c) 140 = 10001100
   d) 160 = 10100000
   e) 170 = 10101010

2. A problem: Consider the following 8-bit 2's complement binary numbers. Convert each of them to conventional signed decimal form: (0.1 points each)

   a) 01100100 = 100
   b) 01111000 = 120
   c) 10001100 = -116 *
   d) 10100000 = -96 *
   e) 10101010 = -86 *

3. A problem: Consider the following decimal numbers. Convert each of them to 8-bit 1's complement binary form: (0.1 points each)

   a) 100 = 01100100
   b) 120 = 01111000
   c) -115 = 10001100 *
   d) -95 = 10100000 *
   e) -85 = 10101010 *

   * Note added Feb. 20: In the above two problems, the originally posted answers were in error in the least significant bit.

4. A problem: Consider the following 8-bit binary numbers. Express each in hexidecimal: (0.1 points each)

   a) 01100100 = 64
   b) 01111000 = 78
   c) 10001100 = 8C
   d) 10100000 = A0
   e) 10101010 = AA

5. Background: Here is a quotation from machine problem 1, with line numbers added for reference:

   14  ITEM1:  W       TEXT1           ; pointer to text
   15          H       5               ; X = 5
   16          H       1               ; Y = 1
   17  
   18  ITEM2:  W       TEXT2
   19          H       2, 1            ; an alternative compacted form
   20  
   21  ITEM3:W SOMETEXT
   22  H 2,2; don't write code like this, it works but it's hard to read
   23  SOMETEXT:ASCII"world",0
   24  
   25  TEXT1:  ASCII   "lo", 0
   26  TEXT2:  ASCII   "Hel", 0
   

   Lines 18-19 are in a style different from that of lines 14-16. Lines 21-23 are a deliberate example of horrible abuse of programming style.

   A problem: Rewrite lines 18-26 so that the style is consistent with the style used in lines 14-17. Your code need not put data into memory in the same order as the original, but it should mean the same thing in the context of machine problem 1. Legible and neat handwritten work is acceptable on this assignment. (1 point)

   In the following solution, I retained the line numbers from the original, where, for every line I changed, I added a suffix to the line number (A for the first line, B for the second, etc.)

   14  ITEM1:  W       TEXT1           ; pointer to text
   15          H       5               ; X = 5
   16          H       1               ; Y = 1
   17  
   18  ITEM2:  W       TEXT2           ; pointer to text
   19A         H       2               ; X = 2
   19B         H       1               ; Y = 1
   20  
   21A ITEM3:  W       TEXT3           ; pointer to text
   22A         H       2               ; X = 2
   22A         H       2               ; Y = 2
   24  
   25  TEXT1:  ASCII   "lo", 0
   26  TEXT2:  ASCII   "Hel", 0
   23A TEXT3:  ASCII   "world",0