CSC231 Homework 7 Fall 2012

--D. Thiebaut 13:47, 24 October 2012 (EDT)

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This assignment is due the evening of Oct. 31st, at midnight (booo!). You can work on this assignment in pairs.

Problem #1 (0.5 point doc, 1.5 points program)

Write a program that displays the contents of a double-word in hexadecimal. Your program should store the value 0x1234ABCD in a variable called x and should display this information:

  x = 305441741 = 0x1234ABCD

where 305441741 is printed by a call to print_int, and 0x1234ABCD is printed by your program.

Submission

Submit your program (called hw7a.asm) as follows:

 rsubmit hw7 hw7a.asm

Hints

HexChars        db          "0123456789ABCDEF"

Problem #2 (0.5 point doc, 1.5 points program)

Take a look at the section of the ASCII table below:

Concentrate on the hexadecimal code for each letter. You will notice that 'A' through 'O' have the same upper nybble. 'A' is 0x41 and 'O' is 0x4F. So, if I wanted to squeeze a string made of upper-case letters between 'A' and 'O', I would only need to store the lower nybble, and I'd save some memory.

The purpose of this problem is for you to take a string created using this method, decode it, and print it on the screen.

Let's look at an example. Look at the 2 variables below. xLen is a double word, and contains 18. That represents the number of bytes containing the characters of the original string. Since each byte of x contains 2 nybbles that are the lower parts of two different characters, then xLen is the number of pairs of nybbles.

Let's take a look at x now. The first byte of x is 0xd1, which means that the first two characters of the original string are 0x4d and 0x41, or 'M' and 'A'. So your program will output 'M' then 'A' when it decodes the string.

xLen     dd     18
x        db     0xd1, 0x41, 0xd5, 0x03, 0x81, 0xee, 0x5c, 0x0d
         db     0x55, 0x40, 0x21, 0x40, 0xd1, 0xe0, 0x9e, 0x0c, 0x9d, 0x10

Your program must decode the two strings listed below and print them on the screen. Your program should replace the character '@' with a space when it prints it.

yLen     dd     18
y        db     0xd5, 0x54, 0x00, 0x31, 0xe4, 0x94, 0x0f, 0x21, 0xd1
         db     0x01, 0xe4, 0x02, 0xfe, 0x90, 0xf6, 0x07, 0x1e, 0x10

zLen     dd     22
z        db     0xef, 0x07, 0xff, 0x40, 0xd1, 0x41, 0xd5, 0x03, 0x81
         db     0xee, 0x5c, 0x0d, 0x55, 0x40, 0x21, 0x40, 0xd1, 0xe0
         db     0x9e, 0x0c, 0x9d, 0x10

Note: You do not need to use functions to solve this problem, but they will make your life easier. Suggestion if you are starting on this on Wednesday 10/24 or Thursday 10/25: write the code for decoding 1 string, and wait until Friday's lecture to put this code in a function that will decode any string you pass to it.

Submission

rsubmit hw7 hw7b.asm

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