proc-bitfield

A Rust crate to expressively declare bitfield-like structs, automatically ensuring their correctness at compile time and declaring accessors.

Typical usage

bitfield! {
    #[derive(Clone, Copy, PartialEq, Eq)]
    pub struct Example(pub u16): Debug {
        // A single field spanning the entire bitfield, using an unbounded range
        pub raw: u16 @ ..,

        // Single-bit flags
        pub vblank: bool @ 0,
        pub hblank: bool @ 1,
        pub vcount_match: bool @ 2,

        // Multi-bit field, specified using an inclusive range
        pub irq_mask: u8 @ 3..=5,

        // Bit 6 is ignored

        // Single-bit field, specified using an exclusive range
        pub vcount_compare_high: u8 @ 7..8,

        // 8-bit field specified using its start bit and length
        pub vcount_compare_low: u8 @ 8; 8,
    }
}

Automatic Debug implementation

A fmt::Debug implementation can be implemented automatically for a given bitfield struct by adding : Debug after the tuple struct-like storage type declaration; the generated fmt function will output the type's raw value as well as all of its fields' values.

nightly feature

Optionally, the nightly feature can be enabled to use const Trait functionality: this makes the BitRange and Bit traits be implemented using const fns for all integer types, and enables the option to use const fns for field accessors.

With the feature enabled, const fn accessors can be enabled globally for a struct by replacing struct with const struct (i.e. const struct Example(pub u16)), or on a field-by-field basis by prepending const to its type (i.e. raw: const u16 @ ..).