bitpack.rs

#![allow(unused_macros)]
#![allow(clippy::inconsistent_digit_grouping)]

macro_rules! bitpack_internal {
    ($type:ty; []; ) => {
        (0 as $type, 0)
    };
    ($type:ty; [$num:literal]; $arg:expr) => {{
        let (mut val, mut width) = bitpack_internal!($type; []; );
        val |= $arg & (1 as $type).checked_shl($num).unwrap_or(0).wrapping_sub(1);
        width += $num;
        (val, width)
    }};
    ($type:ty; [$num:literal, $($nums:literal),+]; $arg:expr, $($args:expr),+) => {{
        let (mut val, mut width) = bitpack_internal!($type; [$($nums),+]; $($args),+);
        val |= ($arg & ((1 << $num) - 1)) << width;
        width += $num;
        (val, width)
    }};
}
macro_rules! bitpack {
    ($type:ty; [$($nums:literal),*]; $($args:expr),*) => {
        bitpack_internal!($type; [$($nums),*]; $($args),*).0
    };
}

#[cfg(test)]
mod tests {
    #[test]
    fn test_u8_pack() {
        let x = 4;
        let y = 2;
        let v = bitpack!(u8; [3, 3, 2]; x, 0, y);
        assert_eq!(v, 0b100_000_10);
        // 本当はこんな感じに書きたい
        // bitpack!(u8; "{3}000{2}", 4, 2);

        assert_eq!(bitpack!(u8; []; ), 0b00000000);
        assert_eq!(bitpack!(u8; [2]; 3), 0b00000011);
        assert_eq!(bitpack!(u8; [2]; 4), 0b00000000);
        assert_eq!(bitpack!(u8; [2]; 5), 0b00000001);
        assert_eq!(bitpack!(u8; [1, 2]; 1, 2), 0b00000110);
        assert_eq!(bitpack!(u8; [2, 2]; 3, 0), 0b00001100);
        assert_eq!(bitpack!(u8; [3, 2]; 7, 0), 0b00011100);
        assert_eq!(bitpack!(u8; [3, 3, 2]; 4, 7, 0), 0b10011100);
        assert_eq!(bitpack!(u8; [2, 4, 2]; 3, 0, 3), 0b11000011);
        assert_eq!(bitpack!(u8; [1,1,1,1,1,1,1,1]; 1,1,1,1,1,1,1,1), 0b11111111);
        assert_eq!(bitpack!(u8; [1,1,1,1,1,1,1,1]; 1,1,1,0,1,1,0,1), 0b11101101);
        assert_eq!(bitpack!(u8; [8]; 0xFF), 0xFF);
        let v: u32 = bitpack!(u32; [10, 10, 2]; 0b1000000000, 0b1000000000, 0b10);
        assert_eq!(v, 0b1000000000100000000010);
    }
}