在javascript中将32位整数转换为4字节的数据

Question

I was asked to convert the integers to 32-bit binary numbers. So is used integer.toString(2) and got the required value in 32-bit binary format of 0'sand 1's. But actually what I was asked to do is convert the integer into 4 bytes of data. I am unable to get the output as suggested. I have used integer.toString(8) , integer.toString(16) . but of no use.

Example:

 num=1065489844 
 num.toString(2) //Output: 111111100000100001010110110100
 num.toString(8) //Output: 7740412664

Please let me know, where I am lacking.

Answer 1

Now you can use ArrayBuffer and DataView . They are native so the performance will be much better if you need to use it very often.

function toBytesInt32 (num) {
    arr = new ArrayBuffer(4); // an Int32 takes 4 bytes
    view = new DataView(arr);
    view.setUint32(0, num, false); // byteOffset = 0; litteEndian = false
    return arr;
}

equals to

function toBytesInt32 (num) {
    arr = new Uint8Array([
         (num & 0xff000000) >> 24,
         (num & 0x00ff0000) >> 16,
         (num & 0x0000ff00) >> 8,
         (num & 0x000000ff)
    ]);
    return arr.buffer;
}

which use javascript bitwise operators to achieve that.

Answer 2

SEIAROTg's answer does not output a string. I have theroughly tested with both positive and negative numbers and this code will give you a 4 byte string output representing the number in big endien format(2's compliment 0xFFFFFFFF = -1).

var toBytesInt32=function(num) {
    var ascii='';
    for (let i=3;i>=0;i--) {
        ascii+=String.fromCharCode((num>>(8*i))&255);
    }
    return ascii;
};

by the way if you want to go the other way around you can use

var fromBytesInt32=function(numString) {
    var result=0;
    for (let i=3;i>=0;i--) {
        result+=numString.charCodeAt(3-i)<<(8*i);
    }
    return result;
};

to convert a 4 byte string to an integer

Answer 3

if you need a hex format output, here is the code.

/* Convert value as 8-bit unsigned integer to 2 digit hexadecimal number. */

function hex8(val) {
    val &= 0xFF;
    var hex = val.toString(16).toUpperCase();
    return ("00" + hex).slice(-2);
}

/* Convert value as 16-bit unsigned integer to 4 digit hexadecimal number. */

function hex16(val) {
    val &= 0xFFFF;
    var hex = val.toString(16).toUpperCase();
    return ("0000" + hex).slice(-4);
}

/* Convert value as 32-bit unsigned integer to 8 digit hexadecimal number. */

function hex32(val) {
    val &= 0xFFFFFFFF;
    var hex = val.toString(16).toUpperCase();
    return ("00000000" + hex).slice(-8);
}


var num = 1065489844;
console.log("0x" + hex32(num)); // will output 0x3F8215B4