mvbitfield

A bitfield library for Rust.

mvbitfield generates types to work with bit-aligned fields.

Bitfield structs serve roughly the same use cases as C/C++ structs with bit-field members and are:

• Endian-insensitive, packing fields within an integer rather than across bytes or array elements.
• Flexible and type-safe with optional user-defined field accessor types.
• Suitable for FFI and memory-mapped I/O with care, as always.

Bitfield enums are unit-only Rust enums with a declared bit width that provide safe zero-cost conversions to and from an integer type and can be used as accessors in a bitfield struct.

Demo

```rust // Recommended, but not required. The mvbitfield prelude includes // the bitint prelude. use mvbitfield::prelude::*;

bitfield! { #[lsbfirst] // Field packing order. #[derive(PartialOrd, Ord)] // Other attributes pass through. pub struct MyBitfieldStruct: 32 { // The lowest three bits with public bitint::U3 accessors. pub somenumber: 3,

    // The next eight bits with public bitint::U8 accessors.
    pub another_number: 8,

    // No accessors for field names starting with _.
    _padding: 2,

    // Private bitint::U11 accessors.
    internal_number: 11,

    // Skip unused bits, in this case five bits.
    ..,

    // The two next-to-most significant bits with public
    // MyBitfieldEnum accessors.
    pub an_enum: 2 as MyBitfieldEnum,

    // Private bool accessors.
    high_bit_flag: 1 as bool,
}

pub enum MyBitfieldEnum: 2 {
    // Declare up to 2^width unit variants with optional
    // explicit discriminants.
    Three = 3,
    Zero = 0,
    One,

    // Generates `Unused2` to complete the enum.
    ..
}

}

[bitint_literals]

fn main() { // Use generated with* methods to build bitfield structs. let x = MyBitfieldStruct::zero() .withsomenumber(6U3) .withanothernumber(0xa5U8) .withinternalnumber(1025U11) .withanenum(MyBitfieldEnum::One) .withhighbit_flag(true);

// Default accessors return bitints.
assert_eq!(x.some_number(), 6_U3);
assert_eq!(x.some_number().to_primitive(), 6);
assert_eq!(x.another_number(), 0xa5_U8);
assert_eq!(x.another_number().to_primitive(), 0xa5);
assert_eq!(x.internal_number(), 1025_U11);
assert_eq!(x.internal_number().to_primitive(), 1025);

// Custom accessors return the chosen type, which must have Into
// conversions to and from the default accessor bitint.
assert_eq!(x.an_enum(), MyBitfieldEnum::One);
assert_eq!(x.high_bit_flag(), true);

// Zero-cost conversions to and from bitints and to primitive.
// For bitfield structs:
assert_eq!(
    x.to_bitint(),
    0b1_01_00000_10000000001_00_10100101_110_U32,
);
assert_eq!(
    x.to_primitive(),
    0b1_01_00000_10000000001_00_10100101_110,
);
assert_eq!(x, MyBitfieldStruct::from_bitint(0xa080252e_U32));
// For bitfield enums:
assert_eq!(MyBitfieldEnum::One.to_bitint(), 1_U2);
assert_eq!(MyBitfieldEnum::One.to_primitive(), 1);
assert_eq!(
    MyBitfieldEnum::One,
    MyBitfieldEnum::from_bitint(1_U2),
);

// Zero-cost conversion from primitive, only for primitive-sized
// bitfield structs and enums.
assert_eq!(x, MyBitfieldStruct::from_primitive(0xa080252e));
bitfield! { enum MyU8Enum: 8 { X = 192, .. } }
assert_eq!(MyU8Enum::X, MyU8Enum::from_primitive(192));

// Bitfield enums optionally generate placeholder variants for
// unused discriminants with `..`. The name is always "Unused"
// followed by the discriminant value in base 10.
assert_eq!(MyBitfieldEnum::Unused2.to_bitint(), 2_U2);
assert_eq!(
    MyBitfieldEnum::Unused2,
    MyBitfieldEnum::from_bitint(2_U2),
);

} ```