lab17: init

lab17/vm.js

@@ -0,0 +1,68 @@
+'use strict';
+
+const fs = require('fs');
+const opcodes = require('./op-codes.js').opcodes;
+
+/**
+ * The VM is responsible for executing the bytecode format.
+ */
+class VirtualMachine {
+
+  /**
+   * Initializes the virtual machine with the specified amount of
+   * gas.  The stack and memory are both initially empty.
+   * 
+   * @param {Number} gas - Amount of gas the VM begins with.
+   */
+  constructor() {
+    this.stack = [];
+    this.memory = [];
+  }
+
+  /** 
+   * Loads a bytecode file and returns an array of strings,
+   * which are the commands within the file.
+   */
+  static loadBytecode(bytecodeFile) {
+    let contents = fs.readFileSync(bytecodeFile);
+    return Buffer.from(contents);
+  }
+
+  /**
+   * Evaluates the specified file.
+   */
+  evaluate(bytecodeFile) {
+    this.bytecode = this.constructor.loadBytecode(bytecodeFile);
+
+    // Initializing the program counter to keep track of our
+    // place within the program.
+    this.pc = 0;
+
+    while (this.pc < this.bytecode.length) {
+      let opcode = this.bytecode.readUInt8(this.pc);
+      //console.log(`Evaluating ${opcode.toString(16)}`);
+      let operation = opcodes[opcode];
+      if (operation === undefined) {
+        throw new Error(`Unable to find instruction for ${opcode.toString(16)}`);
+      }
+      operation.evaluate(this);
+
+      this.pc++;
+    }
+  }
+}
+
+// Handling command line arguments.
+if (process.argv0 === 'node') {
+  process.argv.shift();
+}
+if (process.argv.length !== 2) {
+  console.log("vm.js <bytecode file>");
+  process.exit(1);
+}
+
+let bytecodeFile = process.argv[1];
+
+console.log(`Executing ${bytecodeFile}...`);
+let vm = new VirtualMachine();
+vm.evaluate(bytecodeFile);