README.md

Homework 1

Assignment: Simple C-to-Assembly Compiler

Deadline soft: 6 aprilie 2025, 11:55PM

Deadline hard: 11 aprilie 2025, 11:55PM

Authors

• Robert Grancsa
• Adelina Alexe

Introduction

In a neon-lit room filled with vintage circuit boards and digital memes, Alex—a modern TikTok brain rot specialist—devised a daring plan to escape Instagram’s endless scroll. Determined to reclaim his mind, he crafted a groundbreaking compiler that transformed addictive algorithms into streams of artful data. With every line of code, toxic noise became immersive stories, intricate music, and thought-provoking visuals, forging a digital sanctuary where creativity reigned. As the algorithmic chains broke, Alex emerged as a quiet revolutionary—a cyber alchemist turning the toxic into transcendent.

Objective

Develop a small compiler or translator that converts simple C-like code snippets into basic assembly instructions. The primary goal is to familiarize yourself with assembly language mnemonics and to understand how high-level constructs map to low-level operations. This assignment is intentionally minimalistic to ease you into both assembly language and compiler design. If we actually want to be pedantic, this is actually a transpiler implementation.

Theme

Simple C Statements → Real Assembly The translation should be as simple as possible while covering basic arithmetic operations, register usage, data movement, and control flow constructs. On an lower level, this is what happens in the background when compiling a C program, but it is simplified for easier implementations. If you are really intersted about how a compiler works in reality, we recommend you the 4th year course of Compilers

Conventions and Guidelines

Because we want to prevent you from having to juggle with registers, we'll use some simple conventions.

• Basic Register Mapping:
  • A → eax
  • B → ebx
  • C → ecx
  • D → edx
• Data types
  • We'll assume all of the data types are 4 bytes
  • When you see a number, we will treat it as a int (4 bytes)
  • When handling pointers, those will also be stored as 4 bytes

Instructions

MOV

The mov instructions is the simplest of all, and as the name says, it moves the data from one place to another. More details here

Usage

MOV destination, source

C - ASM translation

C Code	ASM Code
a = 1;	MOV eax, 1
b = a;	MOV ebx, eax

Note: There will be no MOV 2, eax as that is an invalid operation

Logical operations

Usage

AND destination, source OR destination, source XOR destination, source

C - ASM translation

C Code	ASM Code
a = a & 0xFF;	AND eax, 0xFF
b = b | a	OR ebx, eax
c = a ^ c;	XOR ecx, eax

Arithmetic operations

There are 4 aritmetic operations, but we will take them 2 by two, as there are differences between them. The first two, add and sub, are for + and - operations. These work the same way as the MOV instructions.

Usage - add, sub

SUB destination, source

C - ASM translation

C Code	ASM Code
a = a + 5;	ADD eax, 5
b = b - a;	SUB ebx, eax

Usage - mul, div

MUL source2 DIV divisor

You might be wondering, why only one operand? Here we have a special rule, and goes something like this:

When multiplying with MUL, the multiplication will actually take EAX and source2 as the multiplication values, and set them in 2 registers -> EDX and EAX. EDX will store the higher values, and EAX the lower one, acting as a big 8 byte register, because after multiplying two 32 bit number, we might have an overflow. Looking at the table will make it a bit clearer.

Similar to MUL, DIV works with EAX as the primary operand, but it also considers EDX as part of the dividend. This means the division is performed using a 64-bit value (EDX:EAX) divided by the given divisor. The result is stored in EAX, while the remainder is placed in EDX.

C Code	ASM Code
a = a * 3;	MUL 3
b = b * c;	MOV eax, ebx
	MUL ecx
	MOV ebx, eax
a = a / 3;	MOV eax, a
	DIV 3
	MOV a, eax
b = b / c;	MOV eax, ebx
	DIV ecx
	MOV ebx, eax

Note: For simplicity, we will never use eax as source2, and we will never never use the value from EDX.

If you use the DIV instruction with a divisor of 0, the processor will generate a "Divide Error" exception, and the program will stop if it is not handled.

Since division requires EDX to be set up properly, we should always zero it before performing DIV if we are working with unsigned values.

Shift operations

SHL (Shift left) and SHR (Shift right) are bitwise shift instructions.

Usage - shl, shr

SHL destination, no_bits_shifted

SHR destination, no_bits_shifted

• SHL: Moves bits to the left, filling the rightmost bits with zeros. Each shift effectively multiplies the value by 2.

  • Example: 00001100 (12 in decimal) shifted left by 1 becomes 00011000 (24 in decimal).

• SHR: Moves bits to the right, filling the leftmost bits with zeros. Each shift effectively divides the value by 2.

  • Example: 00001100 (12 in decimal) shifted left by 1 becomes 00000110 (6 in decimal).

C Code	ASM Code
a = a << 1	SHL eax, 1
b = b >> 2	SHR ebx, 2

Conditional Statements

CMP Instrunction

CMP instruction compares two values by substracting the second operand from the first. It updates CPU flags, but does not store the result.

Usage - cmp

CMP operand1, operand2

• Example:

  MOV eax, 3

  CMP eax, 3 ; Compares eax with 3

  JE equal_label ; Jumps to label "equal_label" if eax == 3 (Zero flag is set)

Jumps

Here's a short description of each conditional jump:

• JMP (Jump): Jumps to the given label.
• JE (Jump if Equal): Jumps to the given label if the two compared values are equal (e.g.: CMP sets the Zero Flag).
• JNE (Jump if Not Equal): Jumps if the two values are not equal (Zero Flag is not set).
• JG (Jump if Greater): Jumps if the first value is greater than the second (Signed comparison).
• JGE (Jump if Greater or Equal): Jumps if the first value is greater than or equal to the second.
• JL (Jump if Less): Jumps if the first value is less than the second.
• JLE (Jump if Less or Equal): Jumps if the first value is less than or equal to the second.

Usage

JMP label

JE label

JNE label

JG label

JL label

C - ASM translation

C Code	ASM Code
if (a == b) {	CMP eax, ebx
	JNE else_label
// some code here	; some code here
	JMP end_if
} else {	else_label:
some other code here	; some other code here
}	end_if:

Loops - for, while

for loop

C Code	ASM Code
for (a = 0; a < 10; a++) {	MOV eax, 0
	start_loop:
	CMP eax, 10
	JGE end_loop
// some code here	; some code here
	ADD eax, 1
	JMP start_loop
}	end_loop:

while loop

C Code	ASM Code
while (b < 5) {	start_loop:
	CMP ebx, 5
	JGE end_loop
// some code here	; some code that makes b greater than or equal to 5
	JMP start_loop
}	end_loop:

Coding style

Coding style can be run directly in the checker, by pressing C, or by using the cs.sh executable from checker/cs. The points are the folowing:

• >= 10 of CHECK => -5 points
• >= 5 of WARNING => -5 points
• >= 1 of ERROR => -10 points

Notes

• The implementation can be done in any file, and the executable must be named transpiler, situated in the root of the folder, same as the initial makefile does
• For sending the homework, you can use the make pack rule, which automatically creates a zip file with the necesarry content already in it. Don't forget to change your name first

Checker

! Atention, the checker doesn't run valgrind by default, but you must pass all the test with valgrind in order to get the score. To activate valgrind on your checker, press v, making sure there is a red border which will show that it is on.

Instalation steps

You can use the ./install.sh to install all the dependencies and the checker. If you find any errors along this process, try to follow the steps below:

1. Download rustup using curl https://sh.rustup.rs -sSf | sh -s -- -y. If you get any errors after this step, add cargo to the PATH variable using source "$HOME/.cargo/env".

2. Run the following command to install the checker

$ cargo install hw_checker

After install, you can use the hw_checker command to run the checker.

Instructiuni checker

For a list of commands and guides for the checker, please read the README from the src/ directory. If you have any problems running the GUI, you can use the hw_checker --legacy command to run them in text only mode.