92 lines
2.7 KiB
JavaScript
92 lines
2.7 KiB
JavaScript
// Syntax:
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// ADD $01 ; comments follow a `;`
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// ADD $FF ; this is direct addressing
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// ADD ($CC) ; this is indirect addressing
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// END ; END, CFC, and CHP don't require arguments
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// ; (a default value of 0 will be used as their operand)
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const mnemonicsWithOptionalArgs = ['end', 'cfc', 'chp'];
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const mnemonics2opcodes = {
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end: { direct: 0, indirect: 0 },
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sto: { direct: 1, indirect: 2 },
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lda: { direct: 3, indirect: 4 },
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add: { direct: 5, indirect: 6 },
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sub: { direct: 7, indirect: 8 },
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hop: { direct: 9, indirect: 10 },
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jmp: { direct: 11, indirect: 12 },
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cfc: { direct: 13, indirect: 13 },
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chp: { direct: 14, indirect: 14 },
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};
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function decodeMultipleInstructions(str) {
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let lines = str.split(/\n/); // returns an array of lines
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let output = [];
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lines.forEach( (l) => {
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let decoded = decodeInstruction(l);
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if (decoded) {
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output.push(decoded.op);
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output.push(decoded.arg);
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}
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});
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return new Uint8Array(output);
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}
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/**
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* @param {string} line - A line of assembly code
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* @returns {(object|false)} Either {op: machineOp, arg: 0}, or false if the line was blank
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*/
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function decodeInstruction(line) {
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line = stripWhitespaceFromEnds(stripComments(line));
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let op_arg_array = line.split(" "); // split line into an array of [op, arg]
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let opName = op_arg_array[0].toLowerCase();
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let addressingMode = 'direct'; // Must be "direct" or "indirect"
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// Handle blank lines and mnemonics without arguments (eg END)
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if (op_arg_array.length < 2) { // No argument
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// handle blank lines, or lines that just contain a comment:
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if (line.length === 0) { return false; }
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// handle mnemonics that aren't paired with an argument:
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if (mnemonicsWithOptionalArgs.indexOf(opName) < 0) {
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console.error(`Missing opcode: ${line}`);
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throw new Error("Missing opcode");
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}
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let machineOp = mnemonics2opcodes[opName][addressingMode];
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return { op: machineOp, arg: 0 };
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}
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// Handle mnemonics with arguments (eg ADD $FF)
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let arg_str = op_arg_array[1];
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if (arg_str.startsWith("(")) {
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addressingMode = "indirect";
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arg_str = arg_str.replace("(", "");
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arg_str = arg_str.replace(")", "");
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}
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if (arg_str.startsWith("$")) {
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arg_str = arg_str.replace("$", "");
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arg_num = hex2num(arg_str);
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} else {
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arg_num = parseInt(arg_str);
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}
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let machineOp = mnemonics2opcodes[opName][addressingMode];
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return { op: machineOp, arg: arg_num };
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}
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function stripComments(line) {
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return line.replace(/;.+/,"");
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}
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function stripWhitespaceFromEnds(line) {
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line = line.replace(/^\s+/,"");
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line = line.replace(/\s+$/,"");
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return line;
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}
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function hex2num(hex) { return parseInt(hex, 16) };
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// RUN IT
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exports.assemble = (str) => {
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return decodeMultipleInstructions(str);
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} |