[JS][6kyu] MIDI Files: Variable Length Quantity

codewars/6kyu/midi-files-variable-length-quantity/koronya.js

@@ -0,0 +1,97 @@
+// [JS][6kyu] MIDI Files: Variable Length Quantity
+// midi-files-variable-length-quantity
+// https://www.codewars.com/kata/6a020680357f9fb3614e6502/train/javascript
+
+const convertHexToBinary = (n) => n.toString(2).padStart(8, '0')
+const convertBinaryToDecimal = (binary) => parseInt(binary, 2)
+
+const encode = (n) => {
+  if (n === 0) {
+    return [0]
+  }
+  const resultArr = []
+
+  let num = n
+  while (num > 0) {
+    const remainder = num % 128
+    resultArr.push(remainder)
+    num = Math.floor(num / 128)
+  }
+
+  return resultArr.map((value, index) => (index === 0 ? value : value + 128)).reverse()
+}
+
+const decode = (data) => {
+  const resultArr = []
+  let resultStr = ''
+  const dataLength = data.length
+  for (let i = 0; i < dataLength; i += 1 || 0) {
+    const binary = convertHexToBinary(data[i])
+    const continuationBit = binary[0]
+    const valueBits = binary.slice(1)
+    resultArr.push(valueBits)
+    resultStr += valueBits
+    if (continuationBit === '0') {
+      break
+    }
+  }
+
+  return convertBinaryToDecimal(resultStr)
+}
+
+// assert.deepEqual = function (actual, expected) {
+//   if (JSON.stringify(actual) !== JSON.stringify(expected)) {
+//     throw new Error(`Expected ${JSON.stringify(expected)}, but got ${JSON.stringify(actual)}`)
+//   }
+// }
+
+// assert.strictEqual = function (actual, expected) {
+//   if (actual !== expected) {
+//     throw new Error(`Expected ${expected}, but got ${actual}`)
+//   }
+// }
+
+// assert.deepEqual(encode(0), [0x00])
+// assert.deepEqual(encode(127), [0x7f])
+// assert.deepEqual(encode(55), [0x37])
+// assert.deepEqual(encode(69), [0x45])
+
+// assert.strictEqual(decode([0x00]), 0)
+// assert.strictEqual(decode([0x7f]), 127)
+// assert.strictEqual(decode([0x37]), 55)
+// assert.strictEqual(decode([0x45]), 69)
+// // Extra data in input:
+// assert.strictEqual(decode([0x00, 0x7f, 0x7f]), 0)
+// assert.strictEqual(decode([0x7f, 0x81, 0x00]), 127)
+// assert.strictEqual(decode([0x45, 0x45, 0x45]), 69)
+// assert.strictEqual(decode([0x37, 0xff, 0xff, 0x7f]), 55)
+
+// assert.deepEqual(encode(128), [0x81, 0x00])
+// assert.deepEqual(encode(16383), [0xff, 0x7f])
+// assert.deepEqual(encode(8192), [0xc0, 0x00])
+// assert.deepEqual(encode(6969), [0xb6, 0x39])
+
+// assert.strictEqual(decode([0x81, 0x00]), 128)
+// assert.strictEqual(decode([0xff, 0x7f]), 16383)
+// assert.strictEqual(decode([0xc0, 0x00]), 8192)
+// assert.strictEqual(decode([0xb6, 0x39]), 6969)
+// // Extra data in input:
+// assert.strictEqual(decode([0x81, 0x00, 0xff]), 128)
+// assert.strictEqual(decode([0xff, 0x7f, 0x00]), 16383)
+// assert.strictEqual(decode([0xc0, 0x00, 0x81, 0x80, 0x00]), 8192)
+// assert.strictEqual(decode([0xb6, 0x39, 0xff, 0xff]), 6969)
+
+// assert.deepEqual(encode(2097152), [0x81, 0x80, 0x80, 0x00])
+// assert.deepEqual(encode(268435455), [0xff, 0xff, 0xff, 0x7f])
+// assert.deepEqual(encode(134217728), [0xc0, 0x80, 0x80, 0x00])
+// assert.deepEqual(encode(69696969), [0xa1, 0x9d, 0xfb, 0x49])
+
+// assert.strictEqual(decode([0x81, 0x80, 0x80, 0x00]), 2097152)
+// assert.strictEqual(decode([0xff, 0xff, 0xff, 0x7f]), 268435455)
+// assert.strictEqual(decode([0xc0, 0x80, 0x80, 0x00]), 134217728)
+// assert.strictEqual(decode([0xa1, 0x9d, 0xfb, 0x49]), 69696969)
+// // Extra data in input:
+// assert.strictEqual(decode([0x81, 0x80, 0x80, 0x00, 0x7f]), 2097152)
+// assert.strictEqual(decode([0xff, 0xff, 0xff, 0x7f, 0x81, 0x00]), 268435455)
+// assert.strictEqual(decode([0xc0, 0x80, 0x80, 0x00, 0xff, 0xff, 0x7f]), 134217728)
+// assert.strictEqual(decode([0xa1, 0x9d, 0xfb, 0x49, 0x00, 0x00]), 69696969)