81 lines
1.4 KiB
Go
81 lines
1.4 KiB
Go
package vm
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import (
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"fmt"
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"monkey/code"
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"monkey/compiler"
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"monkey/object"
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)
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const StackSize = 2048
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type VM struct {
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constants []object.Object
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instructions code.Instructions
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stack []object.Object
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sp int // Always points to the next value. Top of stack is stack[sp-1]
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}
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func New(bytecode *compiler.Bytecode) *VM {
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return &VM{
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constants: bytecode.Constants,
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instructions: bytecode.Instructions,
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stack: make([]object.Object, StackSize),
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sp: 0,
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}
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}
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func (vm *VM) StackTop() object.Object {
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if vm.sp == 0 {
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return nil
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}
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return vm.stack[vm.sp-1]
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}
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func (vm *VM) Run() error {
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for ip := 0; ip < len(vm.instructions); ip++ {
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op := code.Opcode(vm.instructions[ip])
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switch op {
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case code.OpConstant:
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constIndex := code.ReadUint16(vm.instructions[ip+1:])
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ip += 2
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err := vm.push(vm.constants[constIndex])
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if err != nil {
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return err
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}
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case code.OpAdd:
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right := vm.pop()
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left := vm.pop()
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leftValue := left.(*object.Integer).Value
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rightValue := right.(*object.Integer).Value
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result := leftValue + rightValue
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vm.push(&object.Integer{Value: result})
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}
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}
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return nil
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}
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func (vm *VM) push(o object.Object) error {
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if vm.sp >= StackSize {
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return fmt.Errorf("stack overflow")
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}
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vm.stack[vm.sp] = o
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vm.sp++
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return nil
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}
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func (vm *VM) pop() object.Object {
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o := vm.stack[vm.sp-1]
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vm.sp--
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return o
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}
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