js byte字节流和数字，字符串之间的转换，包含无符和有符之间的转换

var numberutil={
	//byte数组转换为int整数
	bytestoint2:function(bytes, off) {
		var b3 = bytes[off] & 0xff;
		var b2 = bytes[off + 1] & 0xff;
		var b1 = bytes[off + 2] & 0xff;
		var b0 = bytes[off + 3] & 0xff;
		return (b0 << 24) | (b1 << 16) | (b2 << 8) | b3;
	},
	//byte数组转换为无符号short整数
	byte2tounsignedshort:function(bytes, off) {
		var high = bytes[off + 1];
		var low = bytes[off];
		return (high << 8 & 0xff00) | (low & 0xff);
	},
	//byte数组转字符串
	bytetostring:function(arr) {
		if (typeof arr === 'string') {
			return arr;
		}
		var str = '',
			_arr = arr;
		for (var i = 0; i < _arr.length; i++) {
			var one = _arr[i].tostring(2),
				v = one.match(/^1+?(?=0)/);
			if (v && one.length == 8) {
				var byteslength = v[0].length;
				var store = _arr[i].tostring(2).slice(7 - byteslength);
				for (var st = 1; st < byteslength; st++) {
					store += _arr[st + i].tostring(2).slice(2);
				}
				str += string.fromcharcode(parseint(store, 2));
				i += byteslength - 1;
			} else {
				str += string.fromcharcode(_arr[i]);
			}
		}
		return str;
	},		
	//int整数转换为4字节的byte数组
	inttobyte4:function(i) {
		var targets =[];
		targets[0] = (i & 0xff);
		targets[1] = (i >> 8 & 0xff);
		targets[2] = (i >> 16 & 0xff);
		targets[3] = (i >> 24 & 0xff);
		return targets;
	},
	//无符号short转换为2字节的byte数组
	unsignedshorttobyte2:function(s){
		var targets = [];
		targets[1] = (s >> 8 & 0xff);
		targets[0] = (s & 0xff);
		return targets;
	},
	//字符串转byte数组
	stringtobyte:function(str) {
		var bytes = new array();
		var len, c;
		len = str.length;
		for(var i = 0; i < len; i++) {
			c = str.charcodeat(i);
			if(c >= 0x010000 && c <= 0x10ffff) {
				bytes.push(((c >> 18) & 0x07) | 0xf0);
				bytes.push(((c >> 12) & 0x3f) | 0x80);
				bytes.push(((c >> 6) & 0x3f) | 0x80);
				bytes.push((c & 0x3f) | 0x80);
			} else if(c >= 0x000800 && c <= 0x00ffff) {
				bytes.push(((c >> 12) & 0x0f) | 0xe0);
				bytes.push(((c >> 6) & 0x3f) | 0x80);
				bytes.push((c & 0x3f) | 0x80);
			} else if(c >= 0x000080 && c <= 0x0007ff) {
				bytes.push(((c >> 6) & 0x1f) | 0xc0);
				bytes.push((c & 0x3f) | 0x80);
			} else {
				bytes.push(c & 0xff);
			}
		}
		return bytes;
	},
	//有符int转无符int
	int2uint:function(i) {
	    if (i >= 0)
	        return i;
	    else
	        4294967296 + i;
	},
	//无符int转有符int
	uint2int:function(i) {
	    if (i <= 2147483647)
	        return i;
	    else
	        return i - 4294967296
	},
	//有符char转无符char
	char2uchar:function(i) {
	    if (i >= 0)
	        return i;
	    else
	        65535 + i;
	},
	//无符char转有符char
	uchar2char:function(i) {
	    if (i <= 32767)
	        return i;
	    else
	        return i - 65535
	},
	//有符byte转无符byte
	bytes2ubytes:function(i) {
	    if (i >= 0)
	        return i;
	    else
	        255 + i;
	},
	//无符byte转有符byte
	ubytes2bytes:function(i) {
	    if (i <= 127)
	        return i;
	    else
	        return i - 255
	}
}