File-Format.md

W8 Bytecode Format (.wb)

This document describes the binary format used to store W8 bytecode for execution by the W8 virtual machine.

Contents

• Byte Order
• W8 Bytecode File Structure
• Magic Signature
• W8 Version
• Bytecode

Byte Order

All multi-byte integer values in the W8 Bytecode format are stored in Little-Endian byte order.

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W8 Bytecode File Structure

Offset	Size	Section
0	5 bytes	Magic
5	6 bytes	W8 Version
11	—	Bytecode

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Magic Signature

The first 5 bytes of the file must be:

4E 56 4D 42 43

(NVMBC)

This signature identifies the file as an W8 Bytecode file.

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W8 Version

Immediately following the magic signature are 6 bytes specifying the version of the W8 with which the file was compiled.

The version is stored as three consecutive u16 values.

<u16><u16><u16>

W8 versions are incompatible with each other: the version stored in the file must exactly match the version of the virtual machine. Otherwise loading the file must fail with a version compatibility error.

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Bytecode

The file header is immediately followed by a stream of instructions.

Instruction Encoding

[opcode: u8]                 — OperationCode (see opcode.rs)
[operand_count: u8]          — number of operands, 0–3
[operand₁]                   — if count ≥ 1
[operand₂]                   — if count ≥ 2
[operand₃]                   — if count ≥ 3

Operand Encoding

Each operand starts with a 1-byte tag followed by its data:

Tag	Type	Data
0x00	Register	1 byte — register number (u8)
0x01	Immediate	8 bytes — value (u64 Little-Endian)