Run results for: Computing the running sum of an array

The main difference between these loops is that the second loop increments i mid-loop so it can avoid a subtraction to get the previous element. This is the kind of operation you would do to get an integral image so the array size is set to the same amount of pixels as a 720p image.

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Run details:

User agent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/139.0.0.0 Safari/537.36

Browser: Chrome 139

Operating system: Linux

Device Platform: Desktop

Date tested: one year ago

Mid-iteration increment (pre)

310/s

Mid-iteration increment (post)

286/s

Normal way

252/s

View exact numbers

Test name	Executions per second
✓ Mid-iteration increment (pre)	310 Ops/sec
Mid-iteration increment (post)	286 Ops/sec
Normal way	252 Ops/sec

HTML Preparation code:

<!--your preparation HTML code goes here-->

Script Preparation code:

var array1 = new Uint16Array(1280 * 720);
for (let i = array1.length; i > 0; i--) {
	array1[i] = Math.round(Math.random() * 3);
}
var array2 = Uint16Array.from(array1);
var array3 = Uint16Array.from(array1);

Tests:

Normal way
const length = array1.length; for (let i = 1; i < length; i++) { array1[i] += array1[i - 1]; }
Mid-iteration increment (post)
const length = array2.length - 1; for (let i = 0; i < length;) { const last = array2[i++]; array2[i] += last; }
Mid-iteration increment (pre)
const length = array3.length - 1; for (let i = 0; i < length;) { const last = array3[i]; array3[++i] += last; }