Rotate module converted to ESM

4 Ops:
- ROT-13
- ROT-47
- Rotate left
- Rotate right
+ module containing common functions

src/core/lib/Rotate.mjs

@@ -0,0 +1,112 @@
+/**
+ * Bit rotation functions.
+ *
+ * @author n1474335 [n1474335@gmail.com]
+ * @copyright Crown Copyright 2016
+ * @license Apache-2.0
+ *
+ * @todo Support for UTF16
+ */
+
+
+/**
+ * Default values for rotation operations
+ */
+export const ROTATE_AMOUNT = 1;
+export const ROTATE_CARRY = false;
+
+
+/**
+ * Runs rotation operations across the input data.
+ *
+ * @param {byteArray} data
+ * @param {number} amount
+ * @param {function} algo - The rotation operation to carry out
+ * @returns {byteArray}
+ */
+export function rot(data, amount, algo) {
+    const result = [];
+    for (let i = 0; i < data.length; i++) {
+        let b = data[i];
+        for (let j = 0; j < amount; j++) {
+            b = algo(b);
+        }
+        result.push(b);
+    }
+    return result;
+}
+
+
+/**
+ * Rotate right bitwise op.
+ *
+ * @param {byte} b
+ * @returns {byte}
+ */
+export function rotr(b) {
+    const bit = (b & 1) << 7;
+    return (b >> 1) | bit;
+}
+
+/**
+ * Rotate left bitwise op.
+ *
+ * @param {byte} b
+ * @returns {byte}
+ */
+export function rotl(b) {
+    const bit = (b >> 7) & 1;
+    return ((b << 1) | bit) & 0xFF;
+}
+
+
+/**
+ * Rotates a byte array to the right by a specific amount as a whole, so that bits are wrapped
+ * from the end of the array to the beginning.
+ *
+ * @private
+ * @param {byteArray} data
+ * @param {number} amount
+ * @returns {byteArray}
+ */
+export function rotrCarry(data, amount) {
+    const result = [];
+    let carryBits = 0,
+        newByte;
+
+    amount = amount % 8;
+    for (let i = 0; i < data.length; i++) {
+        const oldByte = data[i] >>> 0;
+        newByte = (oldByte >> amount) | carryBits;
+        carryBits = (oldByte & (Math.pow(2, amount)-1)) << (8-amount);
+        result.push(newByte);
+    }
+    result[0] |= carryBits;
+    return result;
+}
+
+
+/**
+ * Rotates a byte array to the left by a specific amount as a whole, so that bits are wrapped
+ * from the beginning of the array to the end.
+ *
+ * @private
+ * @param {byteArray} data
+ * @param {number} amount
+ * @returns {byteArray}
+ */
+export function rotlCarry(data, amount) {
+    const result = [];
+    let carryBits = 0,
+        newByte;
+
+    amount = amount % 8;
+    for (let i = data.length-1; i >= 0; i--) {
+        const oldByte = data[i];
+        newByte = ((oldByte << amount) | carryBits) & 0xFF;
+        carryBits = (oldByte >> (8-amount)) & (Math.pow(2, amount)-1);
+        result[i] = (newByte);
+    }
+    result[data.length-1] = result[data.length-1] | carryBits;
+    return result;
+}