78 lines
1.9 KiB
JavaScript
78 lines
1.9 KiB
JavaScript
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"use strict";
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var utils = require("./utils");
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/**
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* The following functions come from pako, from pako/lib/zlib/crc32.js
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* released under the MIT license, see pako https://github.com/nodeca/pako/
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*/
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// Use ordinary array, since untyped makes no boost here
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function makeTable() {
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var c, table = [];
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for(var n =0; n < 256; n++){
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c = n;
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for(var k =0; k < 8; k++){
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c = ((c&1) ? (0xEDB88320 ^ (c >>> 1)) : (c >>> 1));
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}
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table[n] = c;
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}
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return table;
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}
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// Create table on load. Just 255 signed longs. Not a problem.
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var crcTable = makeTable();
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function crc32(crc, buf, len, pos) {
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var t = crcTable, end = pos + len;
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crc = crc ^ (-1);
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for (var i = pos; i < end; i++ ) {
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crc = (crc >>> 8) ^ t[(crc ^ buf[i]) & 0xFF];
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}
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return (crc ^ (-1)); // >>> 0;
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}
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// That's all for the pako functions.
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/**
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* Compute the crc32 of a string.
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* This is almost the same as the function crc32, but for strings. Using the
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* same function for the two use cases leads to horrible performances.
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* @param {Number} crc the starting value of the crc.
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* @param {String} str the string to use.
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* @param {Number} len the length of the string.
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* @param {Number} pos the starting position for the crc32 computation.
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* @return {Number} the computed crc32.
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*/
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function crc32str(crc, str, len, pos) {
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var t = crcTable, end = pos + len;
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crc = crc ^ (-1);
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for (var i = pos; i < end; i++ ) {
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crc = (crc >>> 8) ^ t[(crc ^ str.charCodeAt(i)) & 0xFF];
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}
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return (crc ^ (-1)); // >>> 0;
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}
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module.exports = function crc32wrapper(input, crc) {
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if (typeof input === "undefined" || !input.length) {
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return 0;
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}
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var isArray = utils.getTypeOf(input) !== "string";
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if(isArray) {
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return crc32(crc|0, input, input.length, 0);
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} else {
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return crc32str(crc|0, input, input.length, 0);
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}
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};
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