chapa 0.9.0

Bitfield structs, batteries included!
Documentation 
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use chapa::{bitfield, extract_bits};

#[bitfield(u32, order = lsb0)]
struct RuntimeReg {
    #[bits(0..=31)]
    value: u32,
}

// --- MSB0 tests (bit 0 = MSB of u32) ---

#[test]
fn msb0_single_bit() {
    // Keep only bit 0 (MSB): 1 << 31 = 0x8000_0000
    let masked = extract_bits!(msb0 u32; 0xFFFF_FFFFu32; 0);
    assert_eq!(masked, 0x8000_0000);
}

#[test]
fn msb0_range() {
    // Keep bits 5..=9: 0x07C0_0000
    let masked = extract_bits!(msb0 u32; 0xFFFF_FFFFu32; 5..=9);
    assert_eq!(masked, 0x07C0_0000);
}

#[test]
fn msb0_mixed_single_and_range() {
    // SRR1 <- MSR mapping: keep bits 0, 5-9, 16-31; clear bits 1-4 and 10-15
    let masked = extract_bits!(msb0 u32; 0xFFFF_FFFFu32; 0, 5..=9, 16..=31);
    assert_eq!(masked, !0x783F_0000u32);
}

#[test]
fn msb0_trailing_comma() {
    let a = extract_bits!(msb0 u32; 0xFFFF_FFFFu32; 0, 5..=9, 16..=31,);
    let b = extract_bits!(msb0 u32; 0xFFFF_FFFFu32; 0, 5..=9, 16..=31);
    assert_eq!(a, b);
}

#[test]
fn msb0_zeroes_cleared_bits() {
    // All-ones input: bits 1-4 and 10-15 should be zero
    let masked = extract_bits!(msb0 u32; 0xFFFF_FFFFu32; 0, 5..=9, 16..=31);
    assert_eq!(masked & 0x7800_0000, 0); // bits 1-4 cleared
    assert_eq!(masked & 0x003F_0000, 0); // bits 10-15 cleared
}

#[test]
fn msb0_u8() {
    // u8 is 8 bits wide; bit 0 = 0x80, bit 7 = 0x01
    let masked = extract_bits!(msb0 u8; 0xFFu8; 0, 7);
    assert_eq!(masked, 0x81);
}

#[test]
fn msb0_preserves_zero() {
    let masked = extract_bits!(msb0 u32; 0u32; 0, 5..=9, 16..=31);
    assert_eq!(masked, 0);
}

// --- LSB0 tests (bit 0 = LSB) ---

#[test]
fn lsb0_range() {
    // Keep bits 0..=3 (low nibble)
    let masked = extract_bits!(lsb0 u16; 0xABCDu16; 0..=3);
    assert_eq!(masked, 0x000D);
}

#[test]
fn lsb0_mixed() {
    // Keep bits 0..=3 and 12..=15
    let masked = extract_bits!(lsb0 u16; 0xFFFFu16; 0..=3, 12..=15);
    assert_eq!(masked, 0xF00F);
}

#[test]
fn lsb0_single_bit() {
    let masked = extract_bits!(lsb0 u8; 0xFFu8; 3);
    assert_eq!(masked, 1 << 3);
}

// --- Half-open ranges (`N..M` == `N..=(M-1)`, same as `#[bits(...)]`) ---

#[test]
fn half_open_matches_inclusive() {
    assert_eq!(
        extract_bits!(lsb0 u16; 0xFFFFu16; 0..4, 12..16),
        extract_bits!(lsb0 u16; 0xFFFFu16; 0..=3, 12..=15),
    );
    assert_eq!(
        extract_bits!(msb0 u32; 0xFFFF_FFFFu32; 5..10),
        extract_bits!(msb0 u32; 0xFFFF_FFFFu32; 5..=9),
    );
}

#[test]
fn runtime_bits_and_ranges() {
    let offset = 8u8;
    let high = 24u8;
    let bit = 3u8;

    assert_eq!(
        extract_bits!(lsb0 u32; 0xFFFF_FFFFu32; offset..offset + 8),
        0x0000_FF00,
    );
    assert_eq!(
        extract_bits!(lsb0 u32; 0xFFFF_FFFFu32; bit, high..high + 8),
        0xFF00_0008,
    );

    let reg = RuntimeReg::from_raw(0x1234_5678);
    let masked = extract_bits!(reg; offset..offset + 8);
    assert_eq!(masked.raw(), 0x0000_5600);
}

#[test]
fn empty_half_open_range_selects_nothing() {
    let offset = 0u8;
    assert_eq!(extract_bits!(lsb0 u32; u32::MAX; 0..0), 0);
    assert_eq!(
        extract_bits!(RuntimeReg::from_raw(u32::MAX); offset..offset).raw(),
        0,
    );
}

#[test]
fn literal_forms_remain_const() {
    const MASKED: u32 = extract_bits!(lsb0 u32; u32::MAX; 8..16);
    const EMPTY: u32 = extract_bits!(lsb0 u32; u32::MAX; 0..0);
    assert_eq!(MASKED, 0x0000_FF00);
    assert_eq!(EMPTY, 0);
}