shlomi1993/assemblyproject

This repo documents an implementation of P-String and realated functions in Assembly language as part of Computer Structure course I took at Bar-Ilan university.

AssemblyProject

This repo documents an implementation of P-String and realated functions in Assembly language as part of Computer Structure course I took at Bar-Ilan university.

Background

P-String is a way to save string as an array of chars where the first byte represents the length of the string:

typedef struct {
    char size;
    char string[255];
} Pstring;

In this repo I've implemented a P-String smilar to those in string.h library, but using assembly language.

P-String in the Stack

The pstring "hello" will be stored in the stack as:

Files

1. run_main.s -- program's entry.
2. pstring.s -- implementations of library functions.
3. func_select.s -- implementation of a function that call other functions.

Program's Structure

run_main() gets two strings and two lengths from the user, build two pstrings and send them to run_func() in func_select.s. run_func uses a jump-table (switch-case) to determine what function from pstring.s to use.

Jump-Table / Switch-Case Options:

• 50 / 60 -- pstrlen -- prints the length of the pstring (return the first byte).
• 52 -- replaceChar -- replace a specific char in the p-string.
• 53 -- pstrijcpy -- copy sub-string between index i to index j to another pstring.
• 54 -- swapCase -- change case of English characters.
• 55 -- pstrijcmp -- compare strings from index i to index j.

Notes

• The code is heavily commented.
• IDE: Visual Studio Code.
• Useful document in resources directory: CS107 Handy one-page of x64-86.