Description
Expected Behavior
Clicking on a + block with 0.1 and 0.2 as its arguments should show 0.3 as the result.
Actual Behavior
Clicking on a + block with 0.1 and 0.2 as its arguments shows 0.30000000000000004 as the result.
Example:
Similar results can be seen with asin of 0.5 and other mathematical expressions.
Suggestion
For background information, see: https://0.30000000000000004.com/
One could argue that, since 0.1 and 0.2 cannot be accurately represented in IEEE floating point numbers, it's "correct" to show 0.30000000000000004 as the answer when adding those two values. I would argue that doing so is only valuable to a minority of our audience, and makes working with math more difficult for the majority of our audience.
In my opinion we should consider using something like https://github.com/MikeMcl/decimal.js for math blocks in Scratch so that the results of Scratch math expressions are correct without having to consider the details of IEEE floating point format. For example:
let a = Decimal('0.1');
let b = Decimal('0.2');
let c = a.add(b); // same as Decimal.add('0.1', '0.2')
console.log(c.toString()); // shows "0.3"
console.log(c == 0.3); // shows "true"
console.log(c === 0.3); // shows "false"let a = Decimal('0.5');
let b = a.asin(); // same as Decimal.asin('0.5')
const pi = Decimal.acos(-1);
const radiansToDegrees = Decimal.div(180, pi);
let bDegrees = b.mul(radiansToDegrees);
console.log(bDegrees.toString()); // shows "30"
console.log(bDegrees == 30); // shows "true"
console.log(bDegrees === 30); // shows "false"One downside is that math operations will be somewhat slower. If we do this, we should do at least two kinds of testing:
- Test several complex projects, especially math-driven ones, to see if performance suffers too much, and
- Check for compatibility problems since there may be projects out there relying on the floating-point behavior, for example with equality or inequality tests.