crc32.js

/*
	Modified for Node.js
	By shaffer
*/
/*

https://github.com/esterTion/BiliBili_crc2mid

*/
var BiliBili_midcrc=function(){
	'use strict';
	const CRCPOLYNOMIAL = 0xEDB88320;
	var startTime=new Date().getTime(),
	crctable=new Array(256),
	create_table=function(){
		var crcreg,
		i,j;
		for (i = 0; i < 256; ++i)
		{
			crcreg = i;
			for (j = 0; j < 8; ++j)
			{
				if ((crcreg & 1) != 0)
				{
					crcreg = CRCPOLYNOMIAL ^ (crcreg >>> 1);
				}
				else
				{
					crcreg >>>= 1;
				}
			}
			crctable[i] = crcreg;
		}
	},
	crc32=function(input){
		if(typeof(input)!='string')
			input=input.toString();
		var crcstart = 0xFFFFFFFF, len = input.length, index;
		for(var i=0;i<len;++i){
			index = (crcstart ^ input.charCodeAt(i)) & 0xff;
			crcstart = (crcstart >>> 8) ^ crctable[index];
		}
		return crcstart;
	},
	crc32lastindex=function(input){
		if(typeof(input)!='string')
			input=input.toString();
		var crcstart = 0xFFFFFFFF, len = input.length, index;
		for(var i=0; i<len;++i){
			index = (crcstart ^ input.charCodeAt(i)) & 0xff;
			crcstart = (crcstart >>> 8) ^ crctable[index];
		}
		return index;
	},
	getcrcindex=function(t){
		//if(t>0)
			//t-=256;
		for(var i=0;i<256;i++){
			if(crctable[i] >>> 24 == t)
				return i;
		}
		return -1;
	},
	deepCheck=function(i, index){
		var tc=0x00,str='',
		hash=crc32(i);
		tc = hash & 0xff ^ index[2];
		if (!(tc <= 57 && tc >= 48))
			return [0];
		str+=tc-48;
		hash = crctable[index[2]] ^ (hash >>> 8);
		tc = hash & 0xff ^ index[1];
		if (!(tc <= 57 && tc >= 48))
			return [0];
		str+=tc-48;
		hash = crctable[index[1]] ^ (hash >>> 8);
		tc = hash & 0xff ^ index[0];
		if (!(tc <= 57 && tc >= 48))
			return [0];
		str+=tc-48;
		hash = crctable[index[0]] ^ (hash >>> 8);
		return [1,str];
	};
	create_table();
	var index=new Array(4);
	console.log('初始化耗时：'+(new Date().getTime()-startTime)+'ms');
	return function(input){
		var ht=parseInt('0x'+input)^0xffffffff,
		snum,i,lastindex,deepCheckData;
		for(i=3;i>=0;i--){
			index[3-i]=getcrcindex( ht >>> (i*8) );
			snum=crctable[index[3-i]];
			ht^=snum>>>((3-i)*8);
		}
		for(i=0;i<100000000; i++){
			lastindex = crc32lastindex(i);
			if(lastindex == index[3]){
				deepCheckData=deepCheck(i,index)
				if(deepCheckData[0])
					break;
			}
		}

		if(i==100000000)
			return -1;
		console.log('总耗时：'+(new Date().getTime()-startTime)+'ms');
		return i+''+deepCheckData[1];
	}
}