Converting IEEE 754 from bit stream into float in JavaScript

Question

I have serialized 32-bit floating number using GO language function (math.Float32bits) which returns the floating point number corresponding to the IEEE 754 binary representation. This number is then serialized as 32-bit integer and is read into java script as byte array.

For example, here is actual number:

float: 2.8088086
as byte array:  40 33 c3 85
as hex: 0x4033c385

There is a demo converter that displays the same numbers.

I need to get that same floating number back from byte array in JavaScript and I have no idea how to do that.

Answer 1

Given the data you've described:

var buffer = new ArrayBuffer(4);
var bytes = new Uint8Array(buffer);
bytes[0] = 0x40;
bytes[1] = 0x33;
bytes[2] = 0xc3;
bytes[3] = 0x85;    

We can retrieve the value as a floating-point number using a DataView:

var view = new DataView(buffer);
// If you only had a Uint8Array, you would use bytes.buffer instead of buffer.

console.log(view.getFloat32(0, false));

2.8088085651397705

var buffer = new ArrayBuffer(4);
var bytes = new Uint8Array(buffer);
bytes[0] = 0x40;
bytes[1] = 0x33;
bytes[2] = 0xc3;
bytes[3] = 0x85;    

var view = new DataView(buffer);

console.log(view.getFloat32(0, false));

Answer 2

a little bit different solution, if you cannot use DataView:

var bytes = [ 0x40, 0x33, 0xc3, 0x85 ];
var bits = (bytes[0] << 24) | (bytes[1] << 16) | (bytes[2] << 8) | (bytes[3]);
var sign = ((bits >>> 31) == 0) ? 1.0 : -1.0;
var e = ((bits >>> 23) & 0xff);
var m = (e == 0) ? (bits & 0x7fffff) << 1 : (bits & 0x7fffff) | 0x800000;
var f = sign * m * Math.pow(2, e - 150);

document.write(f);