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Hack Assembler (Java)

A Java implementation of the Hack Assembler from the Nand2Tetris course.
This project translates Hack assembly language (.asm) programs into 16-bit binary machine code (.hack), supporting symbols, labels, and variables.

📌 Features

  • Two-pass assembly:
    • First pass: Builds the symbol table and resolves labels.
    • Second pass: Translates A- and C-instructions into binary.
  • Predefined symbols (R0–R15, SP, LCL, ARG, THIS, THAT, SCREEN, KBD).
  • Custom variables starting at RAM address 16.
  • Parser that strips comments and whitespace.
  • Code module that maps mnemonics to binary codes.
  • Symbol table for managing predefined and user-defined symbols.

📂 Project Structure

├── Main.java # Entry point, assembles given .asm files
├── Assembler.java # Core assembler logic
├── Parser.java # Cleans input, parses commands
├── Instruction_Category.java # Enum for A, C, and LABEL instructions
├── Code.java # Converts mnemonics to binary codes
├── SymbolTable.java # Handles predefined + user-defined symbols
├── *.asm # Example Hack assembly programs
└── *.hack # Generated binary machine code

⚙️ How It Works

  1. Cleaning the Code
    • Cleans the input file from any whitespaces or comments.
  2. First Pass
    • Reads the assembly file and records all labels (LABEL) with their corresponding ROM addresses in the symbol table.
  3. Second Pass
    • Translates instructions line by line:
      • @value → A-instruction (direct address or symbol lookup).
      • dest=comp;jump → C-instruction (binary translation of comp, dest, and jump).
  4. Output
    • Writes a .hack file containing the 16-bit binary machine code.

📝 Example

Input (Add.asm):

@2
D=A
@3
D=D+A
@0
M=D

Output (Add.Hack):

0000000000000010
1110110000010000
0000000000000011
1110000010010000
0000000000000000
1110001100001000

📖 References

  • Nand2Tetris Course
  • The Elements of Computing Systems (Noam Nisan & Shimon Schocken)