mirror of
https://github.com/danbulant/pngjs
synced 2026-05-27 22:02:22 +00:00
79 lines
2.1 KiB
JavaScript
Executable file
79 lines
2.1 KiB
JavaScript
Executable file
// Copyright (c) 2012 Kuba Niegowski
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//
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// Permission is hereby granted, free of charge, to any person obtaining a copy
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// of this software and associated documentation files (the "Software"), to deal
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// in the Software without restriction, including without limitation the rights
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// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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// copies of the Software, and to permit persons to whom the Software is
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// furnished to do so, subject to the following conditions:
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//
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// The above copyright notice and this permission notice shall be included in
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// all copies or substantial portions of the Software.
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//
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// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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// THE SOFTWARE.
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'use strict';
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var util = require('util'),
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Stream = require('stream');
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var CrcStream = module.exports = function() {
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Stream.call(this);
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this._crc = -1;
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this.writable = true;
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};
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util.inherits(CrcStream, Stream);
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CrcStream.prototype.write = function(data) {
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for (var i = 0; i < data.length; i++) {
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this._crc = crcTable[(this._crc ^ data[i]) & 0xff] ^ (this._crc >>> 8);
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}
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return true;
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};
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CrcStream.prototype.end = function(data) {
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if (data) this.write(data);
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this.emit('crc', this.crc32());
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};
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CrcStream.prototype.crc32 = function() {
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return this._crc ^ -1;
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};
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CrcStream.crc32 = function(buf) {
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var crc = -1;
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for (var i = 0; i < buf.length; i++) {
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crc = crcTable[(crc ^ buf[i]) & 0xff] ^ (crc >>> 8);
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}
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return crc ^ -1;
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};
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var crcTable = [];
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for (var i = 0; i < 256; i++) {
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var c = i;
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for (var j = 0; j < 8; j++) {
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if (c & 1) {
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c = 0xedb88320 ^ (c >>> 1);
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} else {
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c = c >>> 1;
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}
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}
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crcTable[i] = c;
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}
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