利用进制转换压缩数字

/*进制转换函数，用于压缩数字，比如Date.now()这样的长数字，用62进制表示，就更短*/
function zipNum(num, radix){
	if(!zipNum.zip){
		zipNum.zip = function(inputNum){
			if(inputNum > 35){//用大写字母表示36-61
				return String.fromCharCode('A'.charCodeAt(0) + inputNum % 36);
			} else if(inputNum > 9){//用小写字母表示10-35
				return String.fromCharCode('a'.charCodeAt(0) + inputNum % 10);
			} else {
				return inputNum;
			}
		}
	}
	var quotient = num, remainder, result;
	if(radix > 36 && radix < 63){
		result = [];
		do {
			remainder = quotient % radix;
			quotient = parseInt(quotient / radix);
			result.push(zipNum.zip(remainder));
		}while(quotient > radix);
		remainder = quotient % radix;
		if(remainder !== 0){
			result.push(zipNum.zip(remainder));
		}
		result = result.reverse().join('');
	} else if(radix > 1 && radix < 36){
		result = num.toString(radix);
	} else {
		result = num;
		window.console && console.warn('radix argument must be between 2 and 62')
	}
	return result;
}

function testSortNum(){
	assertEquals(zipNum(61, 62), 'Z');
	assertEquals(zipNum(62 * 2 - 1, 62), '1Z');
	assertEquals(zipNum(62 * 3 - 1, 62), '2Z');
	assertEquals(zipNum(1361182624991, 62), 'dXN5fJB');
}
testSortNum();