macro_rules! instructions {
    {
        $($variant:ident = $value:expr),* $(,)?
    } => {

        $(
            pub const $variant: InstOp = $value;
        )*

        pub fn inst_name(op: InstOp) -> Option<&'static str> {
            match op {
                $(
                    $value => Some(stringify!($variant)),
                )*
                _ => None,
            }
        }
    };
}
pub type InstOp = u16;

instructions! {
    ADD        = 0x0000,
    MUL        = 0x0001,
    DIV        = 0x0002,
    MOD        = 0x0003,
    INEG       = 0x0004,
    AND        = 0x0005,
    OR         = 0x0006,
    INV        = 0x0007,
    NOT        = 0x0008,
    XOR        = 0x0009,
    SHL        = 0x000a,
    SHR        = 0x000b,
    CMPEQ      = 0x1000,
    CMPLT      = 0x1001,
    JMP        = 0x1100,
    JZ         = 0x1101,
    JNZ        = 0x1102,
    LOAD       = 0x2000,
    REGCOPY    = 0x2001,
    STOREIMM64 = 0x2100,
    STOREIMM32 = 0x2101,
    MEMCOPY    = 0x2200,
    STORE      = 0x2201,
    HALT       = 0xF000,
    NOP        = 0xF001,
}

pub fn inst_len(op: InstOp) -> usize {
    match op {
        // 2 bytes
        HALT | NOP => 2,
        // 4 bytes
        ADD | MUL | DIV | INEG | INV | NOT | MOD | AND | OR | XOR | SHL | SHR | CMPEQ | CMPLT
        | JMP | JZ | JNZ | LOAD | REGCOPY | MEMCOPY | STORE => 4,
        // Immediates - 4+ bytes
        STOREIMM64 => 16,
        STOREIMM32 => 8,
        _ => panic!("unknown instruction op 0x{:04x}", op),
    }
}