mirror of
https://github.com/kkapsner/CanvasBlocker
synced 2024-06-20 18:42:45 +02:00
79 lines
2.3 KiB
JavaScript
79 lines
2.3 KiB
JavaScript
/* jslint moz: true, bitwise: true */
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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(function(){
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"use strict";
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const persistentRnd = Object.create(null);
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exports.persistent = {
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getRng: function(length, window){
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var domain = window.document.location.host;
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if (!persistentRnd[domain]){
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// create the (sub-)domains random numbers if not existing
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persistentRnd[domain] = new Uint8Array(128);
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window.crypto.getRandomValues(persistentRnd[domain]);
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}
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var bitSet = persistentRnd[domain];
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return function(value, i){
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// use the last 7 bits from the value for the index of the
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// random number
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var index = value & 0x7F;
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// use the last 3 bits from the position and the first bit from
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// from the value to get bit to use from the random number
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var bitIndex = ((i & 0x03) << 1) | (value >>> 7);
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// extract the bit
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var bit = (bitSet[index] >>> bitIndex) & 0x01;
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// XOR the bit the the value to alter the last bit of it... or not
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return value ^ bit;
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};
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}
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};
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exports.nonPersistent = {
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getRng: function(length, window){
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// Initialize the random number batch creation
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var randomI = 65536;
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var randomNumbers = new Uint8Array(Math.min(65536, length));
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return function(value, i){
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if (randomI >= randomNumbers.length){
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// refill the random number bucket if empty
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randomI = 0;
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if (length - i < 65536){
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randomNumbers = new Uint8Array(length - i);
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}
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window.crypto.getRandomValues(randomNumbers);
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}
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var rnd = randomNumbers[randomI];
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randomI += 1;
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// do not alter the most significant bit that is set and
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// the bit after it, to not disturb the image too much.
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if (value >= 0x80){
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value = value ^ (rnd & 0x1F);
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}
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else if (value >= 0x40){
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value = value ^ (rnd & 0x0F);
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}
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else if (value >= 0x20){
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value = value ^ (rnd & 0x07);
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}
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else if (value >= 0x10){
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value = value ^ (rnd & 0x03);
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}
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else if (value >= 0x08){
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value = value ^ (rnd & 0x01);
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}
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// else if (value >= 0x04){
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// value = value ^ (rnd * 0x00);
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// }
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return value;
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};
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}
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};
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}());
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