neobit

A zero-dependency, bitflags macro for systems programming. Designed for no_std environments.

Why neobit?

Bit operations are simple. The library should be too.

neobit provides union, intersection, difference, complement, and membership testing. Nothing more, nothing less.

Quick Start

use neobit::neobit;

neobit! {
    pub struct Permissions: u8 {
        const READ    = 0b001;
        const WRITE   = 0b010;
        const EXECUTE = 0b100;
    }
}

fn main() {
    let perms = Permissions::READ | Permissions::WRITE;

    assert!(perms.contains(Permissions::READ));
    assert!(!perms.contains(Permissions::EXECUTE));

    println!("{:?}", perms);  // Permissions(READ | WRITE)
    
    // All defined flags
    let all = Permissions::all();
    
    // Bit validation
    let valid = Permissions::from_bits(0b011);    // Some(...)
    let invalid = Permissions::from_bits(0b1000); // None
}

Features

• Zero dependencies - Pure Rust, nothing else
• no_std compatible - Works in embedded environments
• All integer types - u8-u128 and i8-i128
• Readable debug output - Flags(READ | WRITE) instead of Flags { bits: 3 }
• const fn operations - Use in const contexts
• Pure bitwise complement - !flags inverts all bits, not just known flags

Use Cases

• Hardware register manipulation
• Network protocol flags
• System call flags (C FFI)
• Embedded systems (no_std)
• Security-sensitive projects requiring easy code audit

Limitations

Composite Constants in Macro

Composite constants can be defined in the macro, but require using .union().bits() syntax:

neobit! {
    pub struct Flags: u8 {
        const A = 0b001;     // ✅ Single bit
        const B = 0b010;     // ✅ Single bit
        const AB = Self::A.union(Self::B).bits();  // ✅ Composite constant - requires .bits()
    }
}

Alternatively, define composite constants outside the macro for cleaner syntax:

impl Flags {
    pub const AB: Self = Self::A.union(Self::B);  // ✅ Cleaner approach
}

API Overview

Construction

Flags::empty()              // No flags set
Flags::all()                // All defined flags
Flags::from_bits(bits)      // Validated, returns Option<Self>
Flags::from_bits_truncate(bits)  // Truncate unknown bits
Flags::from_bits_retain(bits)    // Keep all bits (for FFI)

Operations

flags.contains(other)       // All bits in other are in flags
flags.intersects(other)     // Any bits in other are in flags
flags.is_empty()            // No bits set
flags.is_all()              // All defined flags set
flags.bits()                // Raw bit value

Mutation

flags.insert(other)         // Add flags
flags.remove(other)         // Remove flags
flags.toggle(other)         // Flip flags
flags.set(other, condition) // Set or remove based on bool

Operators

| Operator | Meaning | const fn equivalent | | |----------|---------|---------------------| | | \| | Union | union() | | & | Intersection | intersection() | | ^ | Symmetric difference | symmetric_difference() | | ! | Complement | complement() | | - | Difference | difference() |

All operators have *Assign variants (|=, &=, etc.).

Const Context

const MASK: Flags = Flags::A.union(Flags::B);
const ALL: Flags = Flags::all();

Type Conversion

// From/Into (uses from_bits_retain)
let flags: Flags = 0b11.into();
let bits: u8 = flags.into();

// Explicit
let flags = Flags::from_bits_retain(0b11);
let bits = flags.bits();

Complement Behavior

neobit and bitflags implement complement() differently:

neobit! {
    pub struct Flags: u8 {
        const A = 0b01;
        const B = 0b10;
    }
}

let flags = Flags::A;  // 0b00000001

// neobit: Pure bitwise NOT
let comp = !flags;     // 0b11111110

// bitflags: Masked to known flags
// !flags             -> 0b00000010

neobit preserves all bit information, which is essential for hardware registers and protocol handling.

Signed Types

Signed integers are supported for C FFI compatibility, but be careful with ! (complement):

neobit! {
    pub struct SignedFlags: i8 {
        const A = 0b0001;
    }
}

let complement = !SignedFlags::A;
// i8: !0b0001 = -2 (two's complement)
// u8: !0b0001 = 254

// Prefer difference() for removing flags:
let all = SignedFlags::all();
let without_a = all.difference(SignedFlags::A);

C FFI Example

use neobit::neobit;

// Define flags matching a C header
neobit! {
    #[repr(transparent)]
    pub struct RegisterFlags: u32 {
        const READY   = 0x01;
        const ERROR   = 0x02;
        const BUSY    = 0x04;
        const DATA_RDY = 0x08;
    }
}

// Safe Rust wrapper around C functions
fn read_status() -> RegisterFlags {
    let raw = read_register();
    RegisterFlags::from_bits_retain(raw)  // Preserves all bits!
}

fn set_ready_flag() {
    let current = read_status();
    let updated = current | RegisterFlags::READY;
    write_register(updated.bits());
}

// See examples/c_ffi_simple.rs for a complete runnable example

Debug Output

Single-bit flags are shown by name. Composite constants are expanded:

println!("{:?}", Flags::READ);                    // Flags(READ)
println!("{:?}", Flags::READ | Flags::WRITE);     // Flags(READ | WRITE)
println!("{:?}", Flags::all());                    // Flags(READ | WRITE | EXECUTE)
println!("{:?}", Flags::empty());                  // Flags(empty)
println!("{:?}", Flags::from_bits_retain(0x80));   // Flags(0x80)

Examples

Check out the examples/ directory for comprehensive demonstrations:

• quick_start.rs - Basic usage with file permissions
• all_method.rs - Using the built-in all() method
• bit_validation.rs - Safe vs unchecked bit operations
• complement_difference.rs - How neobit differs from bitflags
• operators_and_methods.rs - All available operations
• type_conversion.rs - Converting between integers and flags
• c_ffi_simple.rs - C FFI and hardware register example
• limitations.rs - Macro limitations and workarounds

Run them with:

cargo run --example <example_name>

Minimum Rust Version

Rust 1.56 or later.

License

Licensed under either of:

• Apache License, Version 2.0 (LICENSE-APACHE)
• MIT license (LICENSE-MIT)

at your option.