jvm/src/stackframe.rs

use crate::classfile::{ JavaClassFile, AttributeData };

#[derive(Copy, Clone, Debug)]
pub enum Value {
    Boolean(bool),
    Byte(u8),
    Char(u16),
    Short(u16),
    Int(u32),
    Float(u32),
    Reference(u32),
    ReturnAddress(u32),
    Double0(u32),
    Double1(u32),
    Long0(u32),
    Long1(u32),
    Empty(),
}

#[derive(Debug)]
pub struct OperandStack {
    stack: Box<[Value]>,
    depth: u16,
}

impl OperandStack {
    fn new(size: u16) -> Self {
        return OperandStack {
            stack: vec![Value::Empty(); size.into()].into_boxed_slice(),
            depth: 0,
        }
    }
}

#[derive(Debug)]
pub struct StackFrame {
    pub locals: Box<[Value]>,
    pub operand_stack: OperandStack,
    pub class_index: usize,
    pub method_index: u16,
    pub instruction_pointer: u32,
}

impl StackFrame {
    pub fn new(classfile: &JavaClassFile, class_index: usize, method_index: u16, arguments: &[Value]) -> Self {
        let method_info = &classfile.methods[method_index as usize];
        let code_data = match &method_info.attributes[method_info.code_attribute_index].data {
            AttributeData::Code(data) => data,
            _ => unreachable!(),
        };
        let mut locals = vec![Value::Empty(); code_data.max_locals.into()].into_boxed_slice();

        assert!(locals.len() >= arguments.len());

        for (index, v) in arguments.iter().enumerate() {
            locals[index] = *v;
        }

        StackFrame {
            locals,
            operand_stack: OperandStack::new(code_data.max_stack),
            class_index,
            method_index,
            instruction_pointer: 0,
        }
    }
}