Data commit

Task/Variable-length-quantity/JavaScript/variable-length-quantity.js

@@ -0,0 +1,31 @@
+const RADIX = 7;
+const MASK = 2**RADIX - 1;
+
+const octetify = (n)=> {
+	if (n >= 2147483648) {
+		throw new RangeError("Variable Length Quantity not supported for numbers >= 2147483648");
+	}
+	const octets = [];
+	for (let i = n; i != 0; i >>>= RADIX) {
+		octets.push((((i & MASK) + (octets.empty ? 0 : (MASK + 1)))));
+	}
+	octets.reverse();
+	return octets;
+};
+
+const deoctetify = (octets)=>
+	octets.reduce((n, octet)=>
+		(n << RADIX) + (octet & MASK)
+	, 0);
+
+// Test (assuming Node.js)
+
+const assert = require("assert");
+const testNumbers = [ 0x200000, 0x1fffff, 1, 127, 128, 2147483647 /*, 589723405834*/ ]
+
+testNumbers.forEach((number)=> {
+	const octets = octetify(number)
+	console.log(octets);
+	const got_back_number = deoctetify(octets)
+	assert.strictEqual(got_back_number, number);
+});