Assignment Overview

This assignment develops familiarity with arrays in assembly language. You will develop a set of ARM assembly language functions which implement common string operations.

It is worth 30 points (3% of course grade) and must be completed no later than 11:59 PM on Thursday, 11/21.

Assignment Deliverables

The deliverables for this assignment are the following files:

proj10.makefile the makefile which produces proj10 proj10.support.s the source code for your support module proj10.driver.c the source code for your driver module

Be sure to use the specified file names and to submit them for grading via the CSE handin system.

Assignment Specifications

A low-level character string is defined as a sequence of zero or more characters in an array of type char, with a null byte to mark the end of the string.

1. You will develop the ARM assembly language functions listed below:

unsigned int length( const char* source );

void copy( char* dest, const char* source );

void append( char* dest, const char* source );

char* duplicate( const char* source );

int compare( const char* source1, const char* source2 );

Those five functions (and any helper functions which you develop) will constitute a module named

proj10.support.s. The functions in that module will not call any C library functions except function malloc.

Function length will return the number of characters in string source; the count will not include the terminating null byte.

Function copy will copy the contents of string source into string dest.

Function append will append the contents of string source to the end of string dest.

Function duplicate will return the address of a duplicate of string source; it will use function malloc to allocation additional memory and will copy string source into that memory.

Function compare will return the results of comparing string source1 and string source2. If source1 and source2 are equal, it will return 0. If source1 is less than source2, it will return a negative integer. If source1 is greater than source2, it will return a positive integer.

2. You will develop a driver module to test your implementation of the support module. The driver module will consist of function main and any additional helper functions which you choose to implement. All output will be appropriately labeled.

Your driver module may not be written as an interactive program, where the user supplies input in response to prompts. Instead, your test cases will be included in the source code as literal constants.

Assignment Notes

1. The functions in your support module must be hand-written ARM assembly language functions (you may not submit compiler-generated assembly language functions).

2. Your program will be translated and linked using gcc. For example, the following commands could be used to translate and link your program, then load and execute it:

<prompt> gcc -c proj10.support.s

<prompt> gcc Wall c proj10.driver.c

<prompt> gcc proj10.support.o proj10.driver.o o proj10 <prompt> proj10

3. In order to interface ARM assembly language functions with C functions, you must follow certain conventions about register usage.

The calling function will place up to four parameters in registers R0 through R3 (with the first argument in register R0).

The called function must save and restore registers R4 through R11 if it uses any of those registers (the calling function assumes that registers R4 through R11 are not altered by calling another function).

The called function place its return value in register R0 before returning to the calling function.

Registers R12, R13, R14 and R15 are used by the system and their contents must not be modified by your functions.