Homework Assignment #3 [50 pts]

You are expected to do your own work on all homework assignments. You may (and are encouraged to) engage in general discussions with your classmates regarding the assignments, but specific details of a solution, including the solution itself, must always be your own work. (See the statement of Academic Dishonesty on the Syllabus.

How to turn in?

Assignments need to be turned in via Laulima. Check the Syllabus for the late assignment policy for the course.

What to turn in?

You must turn in a zip archive named ics312_hw3_xxx.zip, where “xxx” is your UH user name (e.g., for me, it would be ics312_hw3_henric.zip). The archive must contain a single top-level directory called ics312_hw3_xxx, where “xxx” is your UH user name (e.g., for me, it would be ics312_hw3_henric). In that directory you must have all the files named exactly as specified in the questions below.

Expected contents of the ics312_hw3_xxx directory:

• hw3_ex1.asm: code for Exercise #1
• hw3_ex2.asm: code for Exercise #2
• asm_io.asm: I/O functions source code
• asm_io.inc: I/O include file
• driver.c: C driver
• Makefile: A makefile that compiles all your programs into executables (we must just be able to type “make” and generate all your executables). See this page for how to have a makefile compile multiple executables. We will only grade those executables that are generated by typing “make”.

Deviation from the above specs will lead to lost points:

• Archive is not a zip archive (-5 pts)
• Archive does not extract as a single directory (-5 pts)
• The name of the directory is incorrect (-5 pts)
• The asm_io.asm file is missing (-5 pts)
• The asm_io.inc file is missing (-5 pts)
• The driver.c file is missing (-5 pts)
• The .asm homework files are not named correctly (-5 pts)
• The Makefile does not compile all executables (-10 pts)
• The archive is empty, or doesn’t extract, or does not contain a makefile: no credits for the assignment

Exercise 1: Warm Up [20pts]

Write an assembly program called hw3_ex1, with source in file hw3_ex1.asm, that prompts the user for two signed 4-byte integers x and y and prints 3x - 2y + 12. We haven’t seen the multiplication instruction yet, but of course you don’t need it to compute this numerical expression.

Below are program invocation examples (‘%’ is the command-line prompt, and user input is shown as well), and your program should match that output format:

% ./hw3_ex1
Enter integer #1: 2
Enter integer #2: 1
The result is: 16
% ./hw3_ex1
Enter integer #1: -10
Enter integer #2: 13
The result is: -44

You can assume that the user only enters valid input!

Hints:

• Remember that when you print a string it should be null-terminated, meaning that it should have an extra byte with value zero at the end.

Exercise #2: String transformation [30pts]

Write an assembly program called hw3_ex2, with source in file hw3_ex2.asm, that prompts the user for a 3-character string of lower-case letters a to z, s1, and a signed 4-byte integer, x, between 1 and 26 (inclusive). The program then prints a 6-character string, s2. The s2 string is “encoded” as follows:

• s2[0] = upper(s1[0])
• s2[1] = ‘-‘
• s2[2] = s1[2]
• s2[3] = s1[1]
• s2[4] = the x-th letter of the alphabet in upper case
• s2[5] = s1[1]

For instance, if the user enters string “xyz” and integer 4 then the program should print ‘X-zyDy’, that is string s2 in between single quotes, followed by a carriage return.

Below are program invocation examples (‘%’ is the command-line prompt, and user input is shown as well). Your program should match that output format exactly:

./hw3_ex2
Enter a 3-character lower-case string: abc
Enter an integer between 1 and 26: 2
The encoded string is: 'A-cbBb'
% ./hw3_ex2
Enter a 3-character lower-case string: cat
Enter an integer between 1 and 26: 25
The encoded string is: 'C-taYa'

You may assume that the user will always type exactly 3 lower-case characters for the first string followed by a carriage return (linefeed) and then an integer between 1 and 26 (inclusive). That is, you don’t need to worry about invalid input.

Even with our very limited knowledge of assembly, there are quite a few ways to write this program.

Hints:

• Reading a character from the keyboard is done via the read_char macro (see page 17 of the textbook for a description). You’ll have to call this macro 4 times (three times to get the 3 characters in s1 and a fourth time to consume the linefeed).
• Remember that when you print a string it should be null-terminated, meaning that it should have an extra byte with value zero at the end.

EXTRA CREDIT:

• 4 points of extra credit if the program uses no more than 3 calls to print_string and no call to print_char