/**
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* Created by yang on 2015/8/25.
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*/
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'use strict';
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var Buffer = require('buffer').Buffer;
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var trimReg = /^\u0000+|\u0000+$/g;
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module.exports = {
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/**
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* 将unsigned number转换为Big-Endian buffer
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* @param number
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* @param bytes buffer的字节数
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*/
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number2Buffer: function(number, bytes) {
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if (number < 0) {
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throw new Error('"number" must greater than or equal to zero.');
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}
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bytes = bytes || 8;
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// 转换为16进制字符串
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var hex = number.toString(16);
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// ------- 将hex length补充成bytes x 2，不足则高位补0，超过则去掉高位
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var length = hex.length;
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var targetLength = bytes * 2;
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if (length < targetLength) {
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var i = targetLength - length;
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while (i > 0) {
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hex = '0' + hex;
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i--;
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}
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} else if (length > targetLength) {
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hex = hex.substring(length - targetLength);
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}
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// ------ 填充到buffer里，高位在前
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var buffer = new Buffer(bytes);
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var offset = 0;
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while (offset < bytes) {
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var bn = Number("0x" + hex.substring(offset * 2, (offset * 2) + 2));
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buffer.writeUInt8(bn, offset);
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offset++;
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}
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return buffer;
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},
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/**
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* 将buf转为数字
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* @param buf
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* @param offset
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* @returns {number}
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*/
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buffer2Number: function(buf, offset) {
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var str = buf.toString('hex', offset, offset + 8);
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var v = parseInt(str.substring(8), 16) - parseInt(str.substring(0, 8), 16);
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if (v < 0) {
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v--;
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}
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return v;
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},
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/**
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* 构造Object.defineProperty中指定的property属性，并达到const声明的效果，只读，不可写
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* @param value
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* @returns {{configurable: boolean, writable: boolean, value: *}}
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*/
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buildConstProp: function(value) {
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return {
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configurable: false,
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writable: false,
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value: value
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};
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},
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/**
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* 在String.prototype.trim的基础上再去掉\u0000
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* 默认trim的处理见下:
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* https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/String/trim
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* http://blog.stevenlevithan.com/archives/faster-trim-javascript
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* http://jsperf.com/mega-trim-test
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* @param str
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* @returns {string}
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*/
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trim: function(str) {
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return str.trim().replace(trimReg, '');
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},
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/**
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* file id conver to group and filename
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* @param fileId
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* @returns {{group: string, filename: string}}
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*/
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id2gf: function(fileId) {
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var pos = fileId.indexOf('/');
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return {
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group: fileId.substring(0, pos),
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filename: fileId.substring(pos + 1)
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};
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}
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};
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