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mirror of https://github.com/kkapsner/CanvasBlocker synced 2024-12-23 05:10:27 +01:00
CanvasBlocker/lib/randomSupplies.js
2016-08-15 13:27:28 +02:00

79 lines
2.3 KiB
JavaScript

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