CMSC313, Computer Organization & Assembly Language Programming, Fall 2012

Project 4: External Records

Due: Thursday October 11, 2012, 11:59pm

Objective

Assignment

struct {
char realname[32] ;
char nickname[16] ;
char alignment[20] ;
char role[20] ;
int points ;
int level ;

} records[10] ;

int num_records = 10 ;

Your assembly language program must search through the array and find the record with the least number of points and the record with the highest level. It must then print out the realname field of these two records. E.g.,

Lowest Points: James Pressman
Highest Level: Gabriel Lee

Implementation Notes

• The sample data in records.c contains 10 records, but your program should work with any number of records. The number of records is stored in the int variable num_records.

• In order to access the externally defined array and integer variable, you must have the following declaration in your assembly language program:

  extern records, num_records

  This will allow you to use records and num_records as labels for the memory location of the array of records and of the int variable, respectively.

• You must also make your own test cases. The example in records.c does not fully exercise your program. Your program will be graded based upon other test cases.

• You will need to link your assembly language program with the data defined in the C program. Use the following Unix commands:

  gcc -c records.c
  nasm -f elf report.asm
  ld records.o report.o

• An important part of this project is deciding how to use indexed addressing to access the data in the records. Think this through carefully. A clean and logical approach to this problem will yield clean and logical code that is easier to construct and, more importantly, easier to debug.

• Your program should be reasonably robust and report errors encountered (e.g., empty array) rather than crashing.

• To access each field of the record, you should use an offset from the address of the record. You should use %define constants instead of magic numbers. E.g.,

  %define RealnameOffset 0
  %define NickOffset 32
  %define AlignOffset 48
  %define RoleOffset 68
  %define PointsOffset 88
  %define LevelOffset 92
  %define RecSize 96

• When your print out the real names at the end, remember that the strings in each record are C-style null-terminated arrays of characters. Before you make a system call asking to print out the realname field, you must compute the length of the string.

Extra Credit

Nicknames should be compared using dictionary ordering. For example, any string starting with the letter 'a' comes before any string that starts with 'b' (regardless of length). In the case that one string is a prefix of another, the shorter string come first. E.g., "egg" comes before "egghead".

Turning in your program

Use the UNIX submit command on the GL system to turn in your project. You should submit at least 4 files: your assembly language program, at least 2 of your own test cases and a typescript file of sample runs of your program.

The UNIX command to do this should look something like:

submit cs313 proj4 report.asm myrec1.c myrec2.c typescript