🛠️ Two-Pass Assembler — Systems Programming Lab

Welcome to the Two-Pass Assembler Project!
This repository contains a lightweight assembler written in C, developed as part of the Systems Programming Lab course at The Open University of Israel.

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🚀 Overview

This assembler translates a simplified assembly language into 14-bit machine code using a two-pass approach. It supports macro expansion, symbol tables, and generates .ob, .ent, and .ext files.

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✨ Features

✅ Two-pass parsing (symbol resolution + machine code generation)
✅ Supports .data, .string, .entry, .extern, and macro definitions
✅ Symbol table + label management
✅ Outputs .ob, .ent, .ext files per input
✅ Clear error messages with source line tracking

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📁 Project Structure

two-pass-assembler/
├── src/                # Core source and header files
├── test_inputs/        # Sample `.as` input files
├── test_output/        # Output files (.ob, .ent, .ext, .am)
├── makefile            # Build automation
├── README.md           # Project documentation

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⚙️ How to Build & Run

🔧 Build

make

This compiles the assembler into an executable named assembler.

▶️ Run

./assembler test_inputs/input1.as

Generated output will be placed in the test_output/ folder:

• input1.ob – Machine code
• input1.ent – Entries table
• input1.ext – External references

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📝 Example Input (Assembly)

MAIN:   mov     S1.1, W
        add     r2, STR
        stop
STR:    .string "abcdef"
LENGTH: .data   6,-9,15
K:      .data   22
.extern W
.entry  MAIN
.entry  K

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🧠 Machine Code Format (14-bit Encoding)

Each instruction is encoded into a 14-bit word using this structure:

Bits	Field	Description
13–10	Opcode (4 bits)	Operation (mov, add, etc.)
9–7	Source Addressing (3)	Register/addressing mode of source operand
6–4	Dest Addressing (3)	Register/addressing mode of destination
1–0	ARE (2 bits)	A = Absolute, R = Relocatable, E = External

🧾 Example Encoding

Instruction: mov R3, R1
→ Opcode: 0000, Src: 011, Dest: 001, ARE: 00
Result: 00000110010000

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👨‍💻 Authors

👤 Amir Kot (AmirKot
📘 B.Sc. Computer Science, The Open University of Israel
🧑‍🤝‍🧑 Collaborated with GitShiraz11

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📄 License

This project is released under the MIT License.
Free to use, learn from, and improve.

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🙌 Thank You

Thanks for checking out the project!
Feel free to fork, star ⭐ the repo, or open an issue if you'd like to contribute or ask questions.

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🔗 Connect

• 🔗 LinkedIn