整数转二进制

其中num 为整数，length为输出二进制位数

function intToBits(num, length) {

if(isNaN(num) || num === num+1)

return null;

if(typeof length !== "number" || isNaN(length) || length === length+1 || length < 1 || length === undefined)

length = 32;

var origNum = num;

var bits = [];

var importantBits = 1;

for(var i=0; i<32; i++) {

var curBit = num % 2 == 0 ? '0' : '1';

bits.unshift(curBit);

num = num >> 1;//右移一位相当于除2，右移n位相当于除以2的n次方。

if(num !== 0)

importantBits++;

}

return bits.reverse().splice(0,Math.max(importantBits, length)).reverse().join('');

}