letmaik/test.html

## test.html
<!doctype html>
<html>
<body>

DataView: <span id="time_dataview"></span><br />
Inline: <span id="time_inline"></span>

<script>

var littleEndian = (function() {
  var buffer = new ArrayBuffer(2);
  new DataView(buffer).setInt16(0, 256, true);
  return new Int16Array(buffer)[0] === 256;
})();

console.log('little endian: ' + littleEndian)


// create test data, 100MiB, assuming big endian float32's
var len = 26214400
var buf = new ArrayBuffer(len*4)

// Approach A: DataView

var t0 = new Date()

for (var n=0; n<10; n++) {

    // convert floats in buffer to little endian
    var dv = new DataView(buf)
    for (var i=0; i<len+4; i+=4) {
        dv.setFloat32(i, dv.getFloat32(i, false))
    }

}

var t1 = new Date()
var t = ((t1-t0)/10).toFixed(2)
document.getElementById('time_dataview').innerHTML = t;
console.log('convert_endian_dataview: ' + t + 'ms')

// Approach B: inlined code

var t0 = new Date()

var bytes = new Uint8Array(buf)

for (var n=0; n<10; n++) {

    // convert floats in buffer to little endian
    var holder;
    for (var i=0; i<len+4; i+=4) {
        holder = bytes[i];
        bytes[i] = bytes[i+3];
        bytes[i+3] = holder;
        holder = bytes[i+1];
        bytes[i+1] = bytes[i+2];
        bytes[i+2] = holder;
    }

}

var t1 = new Date()
var t = ((t1-t0)/10).toFixed(2)
document.getElementById('time_inline').innerHTML = t;
console.log('convert_endian_inline: ' + t + 'ms')

// now we can create a typed array
var ta = new Float32Array(buf)

</script>

</body>
</html>
	<!doctype html>
	<html>
	<body>

	DataView: <span id="time_dataview"></span><br />
	Inline: <span id="time_inline"></span>

	<script>

	var littleEndian = (function() {
	var buffer = new ArrayBuffer(2);
	new DataView(buffer).setInt16(0, 256, true);
	return new Int16Array(buffer)[0] === 256;
	})();

	console.log('little endian: ' + littleEndian)


	// create test data, 100MiB, assuming big endian float32's
	var len = 26214400
	var buf = new ArrayBuffer(len*4)

	// Approach A: DataView

	var t0 = new Date()

	for (var n=0; n<10; n++) {

	// convert floats in buffer to little endian
	var dv = new DataView(buf)
	for (var i=0; i<len+4; i+=4) {
	dv.setFloat32(i, dv.getFloat32(i, false))
	}

	}

	var t1 = new Date()
	var t = ((t1-t0)/10).toFixed(2)
	document.getElementById('time_dataview').innerHTML = t;
	console.log('convert_endian_dataview: ' + t + 'ms')

	// Approach B: inlined code

	var t0 = new Date()

	var bytes = new Uint8Array(buf)

	for (var n=0; n<10; n++) {

	// convert floats in buffer to little endian
	var holder;
	for (var i=0; i<len+4; i+=4) {
	holder = bytes[i];
	bytes[i] = bytes[i+3];
	bytes[i+3] = holder;
	holder = bytes[i+1];
	bytes[i+1] = bytes[i+2];
	bytes[i+2] = holder;
	}

	}

	var t1 = new Date()
	var t = ((t1-t0)/10).toFixed(2)
	document.getElementById('time_inline').innerHTML = t;
	console.log('convert_endian_inline: ' + t + 'ms')

	// now we can create a typed array
	var ta = new Float32Array(buf)

	</script>

	</body>
	</html>