x86 Assembly Coursework

Solutions to two university assignments written in 32-bit x86 assembly (NASM syntax), with the functions called from C. Each homework lives in its own directory and has a README explaining, task by task, how the implementation works, register layout, auxiliary variables, and the role of every label.

Contents

Homework 2

Task	Problem	Key idea
1	Filter an array, keeping even numbers that are not powers of two	test for parity, x & (x - 1) for the power-of-two check
2	Validate and sort a list of dated events	struc / istruc for nested structures, BubbleSort with a cascade of criteria
3	Base64 encoding	packing 3 × 8 bits into a 24-bit group, then splitting it into 4 × 6 bits with shifts and masks
4	Sudoku validation	range and duplicate checks on rows, columns and 3 × 3 boxes

Homework 3

Task	Problem	Key idea
1	Link array nodes into a sorted linked list	building the list in place while tracking head and tail
2	Split a text into words and sort them	custom comparator passed to libc qsort
3	Recursive k-Fibonacci	recursion with the registers preserved across each call
4	Longest composite palindrome	bitmask enumeration of every subset, with malloc / free for the candidates

Techniques covered

• cdecl calling convention: arguments pushed in reverse order, return value in eax, caller-side stack cleanup
• stack frames with enter / leave, register preservation with pusha / popa and explicit push / pop
• recursion in assembly
• calling libc from assembly: qsort, malloc, free, strlen, strcpy, strcat, strcmp
• bit manipulation: shifts, masks, subset enumeration with bitmasks
• data structures: linked lists, nested structures via struc / istruc, arrays of strings

Building

The sources are assembled for 32-bit x86 and linked against a C driver:

nasm -f elf32 task-1/sortari.asm -o sortari.o
gcc -m32 main.c sortari.o -o task1

All nine sources assemble cleanly on their own. The C drivers and test suites were provided by the course and are not part of this repository, so the functions here are meant to be linked against your own main.