Assembler

A simple two-pass assembler for the Nand2Tetris Hack computer.
This tool translates Hack assembly (.asm) files into binary machine code (.hack), including support for labels, variables, and all standard C‑instructions.

Features

• Full support for the Hack instruction set:
  • A‑instructions: @value (literal or symbol)
  • C‑instructions: dest=comp;jump
• Two-pass (double parsing) symbol resolution:
  • Pass 1: Collects label definitions and ROM addresses
  • Pass 2: Resolves symbols (labels + variables) and emits binary code
• Built‑in predefined symbols (R0–R15, SCREEN, KBD)
• Automatic variable allocation starting at RAM address 16
• Ignores comments (// ...) and whitespace
• Outputs 16‑bit binary .hack files ready to run on the Nand2Tetris CPU emulator

How double parsing works

The assembler uses a classic two‑pass algorithm:

1. First pass (symbol table construction)

   • Reads the assembly file line by line.
   • Strips comments and whitespace.
   • For each label declaration (LABEL):
     • Adds LABEL to the symbol table with the current ROM address.
   • For each actual instruction (A or C):
     • Increments the ROM address counter.

2. Second pass (code generation)

   • Re-reads the assembly file.
   • For A‑instructions:
     • If the symbol is a number, use it directly.
     • If the symbol is not in the table, allocate a new RAM address (starting at 16).
     • Emit a 16‑bit A‑instruction: 0vvvvvvvvvvvvvvv.
   • For C‑instructions:
     • Parse dest, comp, and jump.
     • Map each field to its corresponding bit pattern.
     • Emit a 16‑bit C‑instruction: 111accccccdddjjj.

This double parsing keeps the implementation simple while correctly handling forward references and labels defined later in the file.

Installation

Clone the repository:

git clone https://github.com/nipunattri1/Assembler

Build

cd src
g++ *.cpp -o assembler

Run

./assembler in.asm