Create a simple assembler

sketches/assembler_sketch.js

@@ -0,0 +1,91 @@
+// Usage: `node assembler_sketch.js assembly.asm`
+
+// Syntax:
+// ADD $01   ; comments follow a `;`
+// ADD $FF   ; this is direct addressing
+// ADD ($CC) ; this is indirect addressing
+// END       ; END, CFC, and CHP don't require arguments
+//           ; (a default value of 0 will be used as their operand)
+
+const fs = require('fs');
+const filename = process.argv[2];
+
+const mnemonicsWithOptionalArgs = ['end', 'cfc', 'chp'];
+const mnemonics2opcodes = {
+  end: { direct: 0, indirect: 0 },
+  sto: { direct: 1, indirect: 2 },
+  lda: { direct: 3, indirect: 4 },
+  add: { direct: 5, indirect: 6 },
+  sub: { direct: 7, indirect: 8 },
+  hop: { direct: 9, indirect: 10 },
+  jmp: { direct: 11, indirect: 12 },
+  cfc: { direct: 13, indirect: 13 },
+  chp: { direct: 14, indirect: 14 },
+};
+
+function decodeMultipleInstructions(str) {
+  let lines = str.split(/\n/); // returns an array of lines
+  let output = [];
+  lines.forEach( (l) => {
+    let stripped = stripWhitespaceFromEnds(stripComments(l));
+    let decoded = decodeInstruction(stripped);
+    output.push(decoded.op);
+    output.push(decoded.arg);
+  });
+  return output;
+}
+
+function decodeInstruction(line) {
+  let addressingMode = "direct"; // Must be "direct" or "indirect"
+  op_arg_array = line.split(" ");
+  let opName = op_arg_array[0].toLowerCase();
+
+  // Handle mnemonics without arguments (eg END)
+  if (op_arg_array.length < 2) { // No argument
+    if (mnemonicsWithOptionalArgs.indexOf(opName) < 0) {
+      throw error("Missing opcode");
+    }
+    let machineOp = mnemonics2opcodes[opName][addressingMode];
+    return { op: machineOp, arg: 0 };
+  }
+  // Handle mnemonics with arguments (eg ADD $FF)
+  let arg_str = op_arg_array[1];
+  if (arg_str.startsWith("(")) {
+    addressingMode = "indirect";
+    arg_str = arg_str.replace("(", "");
+    arg_str = arg_str.replace(")", "");
+  }
+  if (arg_str.startsWith("$")) {
+    arg_str = arg_str.replace("$", "");
+    arg_num = hex2num(arg_str);
+  } else {
+    arg_num = parseInt(arg_str);
+  }
+  let machineOp = mnemonics2opcodes[opName][addressingMode];
+  return { op: machineOp, arg: arg_num };
+}
+
+function stripComments(line) {
+  return line.replace(/;.+/,"");
+}
+
+function stripWhitespaceFromEnds(line) {
+  line = line.replace(/^\s+/,"");
+  line = line.replace(/\s+$/,"");
+  return line;
+}
+
+function hex2num(hex) { return parseInt(hex, 16) };
+
+
+
+
+// RUN IT
+
+try {
+  // console.log(`Reading ${filename}`);
+  const inputFile_str = fs.readFileSync(filename, 'utf8');
+  console.log(decodeMultipleInstructions(inputFile_str));
+} catch (err) {
+  console.error(err);
+}