lunify 1.1.0

A crate for converting Lua byte code to different versions and formats
Documentation 
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#[cfg(feature = "serde")]
use serde::{Deserialize, Serialize};

use crate::LunifyError;

#[derive(Clone, Copy, Debug, Default, PartialEq, Eq, PartialOrd, Ord, Hash)]
#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
pub(crate) struct OperandLayout {
    pub(crate) size: u64,
    pub(crate) position: u64,
    pub(crate) bit_mask: u64,
}

impl OperandLayout {
    pub(crate) fn new(size: u64, position: u64) -> Self {
        let bit_mask = !0 >> (64 - size);
        Self { size, position, bit_mask }
    }

    pub(crate) fn get(&self, value: u64) -> u64 {
        (value >> self.position) & self.bit_mask
    }

    pub(crate) fn put(&self, value: u64) -> Result<u64, LunifyError> {
        let maximum_value = (1 << self.size) - 1;

        if value > maximum_value {
            return Err(LunifyError::ValueTooBigForOperand);
        }

        Ok((value & self.bit_mask) << self.position)
    }
}

/// All possible operands of an instruction.
#[derive(Clone, Copy, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]
#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
pub enum OperandType {
    /// Size of the Opcode (`SIZE_O`P).
    Opcode(u64),
    /// Size of the A operand (`SIZE_A`).
    A(u64),
    /// Size of the B operand (`SIZE_B`).
    B(u64),
    /// Size of the C operand (`SIZE_C`).
    C(u64),
}

/// Memory layout of instructions inside the Lua byte code (`SIZE_*`, `POS_*`).
#[derive(Clone, Copy, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]
#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
pub struct InstructionLayout {
    pub(crate) opcode: OperandLayout,
    pub(crate) a: OperandLayout,
    pub(crate) b: OperandLayout,
    pub(crate) c: OperandLayout,
    pub(crate) bx: OperandLayout,
    pub(crate) signed_offset: i64,
}

impl InstructionLayout {
    /// Create a memory layout from a list of [`OperandType`]s.
    ///# Example
    ///
    ///```rust
    /// use lunify::{InstructionLayout, OperandType};
    ///
    /// // This is how the Lua 5.0 InstructionLayout is created.
    /// let layout = InstructionLayout::from_specification([
    ///     OperandType::Opcode(6),
    ///     OperandType::C(9),
    ///     OperandType::B(9),
    ///     OperandType::A(8)
    /// ]);
    /// ```
    pub fn from_specification(specification: [OperandType; 4]) -> Result<Self, LunifyError> {
        let mut opcode = None;
        let mut a = None;
        let mut b = None;
        let mut c = None;
        let mut offset = 0;

        for operand in specification {
            match operand {
                OperandType::Opcode(size) => {
                    // The minimum is 6 because there are 38 instructions in Lua 5.1, so we need a
                    // minimum of `ceil(log2(38))` bits to represent them all.
                    if !(6..32).contains(&size) || opcode.is_some() {
                        return Err(LunifyError::InvalidInstructionLayout);
                    }

                    opcode = Some(OperandLayout::new(size, offset));
                    offset += size;
                }
                OperandType::A(size) => {
                    // The minimum is 7 because A needs to be able to hold values up to
                    // Lua 5.1 `MAXSTACK`.
                    if !(7..32).contains(&size) || a.is_some() {
                        return Err(LunifyError::InvalidInstructionLayout);
                    }

                    a = Some(OperandLayout::new(size, offset));
                    offset += size;
                }
                OperandType::B(size) => {
                    // The minimum is 8 because B needs to be able to hold values up to
                    // Lua 5.1 `MAXSTACK`, plus an additional bit for constant values.
                    if !(8..32).contains(&size) || b.is_some() {
                        return Err(LunifyError::InvalidInstructionLayout);
                    }

                    b = Some(OperandLayout::new(size, offset));
                    offset += size;
                }
                OperandType::C(size) => {
                    // The minimum is 8 because C needs to be able to hold values up to
                    // Lua 5.1 `MAXSTACK`, plus an additional bit for constant values.
                    if !(8..32).contains(&size) || c.is_some() {
                        return Err(LunifyError::InvalidInstructionLayout);
                    }

                    c = Some(OperandLayout::new(size, offset));
                    offset += size;
                }
            }
        }

        let opcode = opcode.unwrap();
        let a = a.unwrap();
        let b = b.unwrap();
        let c = c.unwrap();

        // Make sure that B and C are next to each other.
        if c.position + c.size != b.position && b.position + b.size != c.position {
            return Err(LunifyError::InvalidInstructionLayout);
        }

        let bx_size = b.size + c.size;
        let bx_position = u64::min(b.position, c.position);
        let bx = OperandLayout::new(bx_size, bx_position);
        let signed_offset = (!0u64 >> (64 - bx_size + 1)) as i64;

        Ok(Self {
            opcode,
            a,
            b,
            c,
            bx,
            signed_offset,
        })
    }
}

#[cfg(test)]
mod tests {
    use crate::function::instruction::operand::OperandLayout;
    use crate::{InstructionLayout, LunifyError, OperandType};

    #[test]
    fn layout_new() {
        let layout = OperandLayout::new(8, 6);
        let expected = OperandLayout {
            size: 8,
            position: 6,
            bit_mask: 0b11111111,
        };

        assert_eq!(layout, expected);
    }

    #[test]
    fn layout_get() {
        let layout = OperandLayout::new(2, 2);
        assert_eq!(layout.get(0b11100), 0b11);
    }

    #[test]
    fn layout_put() {
        let layout = OperandLayout::new(2, 2);
        assert_eq!(layout.put(0b11), Ok(0b1100));
    }

    #[test]
    fn layout_put_out_of_bounds() {
        let layout = OperandLayout::new(2, 2);
        assert_eq!(layout.put(0b111), Err(LunifyError::ValueTooBigForOperand));
    }

    #[test]
    fn from_specification() -> Result<(), LunifyError> {
        let layout =
            InstructionLayout::from_specification([OperandType::Opcode(6), OperandType::C(9), OperandType::B(9), OperandType::A(8)])?;

        assert_eq!(layout.opcode.position, 0);
        assert_eq!(layout.a.position, 24);
        assert_eq!(layout.b.position, 15);
        assert_eq!(layout.c.position, 6);
        assert_eq!(layout.bx.position, 6);
        assert_eq!(layout.bx.size, layout.b.size + layout.c.size);
        assert_eq!(layout.signed_offset, 131071);
        Ok(())
    }

    #[test]
    fn from_specification_opcode_twice() {
        let result =
            InstructionLayout::from_specification([OperandType::Opcode(6), OperandType::Opcode(6), OperandType::B(9), OperandType::A(8)]);
        assert_eq!(result, Err(LunifyError::InvalidInstructionLayout));
    }

    #[test]
    fn from_specification_a_twice() {
        let result =
            InstructionLayout::from_specification([OperandType::Opcode(6), OperandType::A(8), OperandType::B(9), OperandType::A(8)]);
        assert_eq!(result, Err(LunifyError::InvalidInstructionLayout));
    }

    #[test]
    fn from_specification_b_twice() {
        let result =
            InstructionLayout::from_specification([OperandType::Opcode(6), OperandType::B(9), OperandType::B(9), OperandType::A(8)]);
        assert_eq!(result, Err(LunifyError::InvalidInstructionLayout));
    }

    #[test]
    fn from_specification_c_twice() {
        let result =
            InstructionLayout::from_specification([OperandType::Opcode(6), OperandType::C(9), OperandType::C(9), OperandType::A(8)]);
        assert_eq!(result, Err(LunifyError::InvalidInstructionLayout));
    }

    #[test]
    fn from_specification_b_and_c_seperated() {
        let result =
            InstructionLayout::from_specification([OperandType::Opcode(6), OperandType::C(9), OperandType::A(9), OperandType::B(8)]);
        assert_eq!(result, Err(LunifyError::InvalidInstructionLayout));
    }
}