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