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Decoding Why 0.6 + 0.3 = 0.8999999999999999 in JS and How to Solve?

Jeeva Ramanathan on November 16, 2023

Understanding IEEE 754 Floating-Point Numbers and also exploring how 0.1+0.2 is 0.30000000000000004 step-by-step While working on an o...

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Paweł bbkr Pabian • Nov 17 '23

Great explanation of IEEE754.

However for all precision-sensitive calculations I recommend Raku, because it automatically does fraction rationals. So if you write 0.12824 it will be represented as 1603/12500 internally:

$ raku -e 'say 0.12824.nude'
(1603 12500)

Fraction calculations will always be performed using integer numerator and denominator, therefore will always be precise:

$ perl -E 'say 0.7 - 0.6 - 0.1'
-2.77555756156289e-17  # FAIL

$ python -c 'print(0.7 - 0.6 - 0.1)'
-2.7755575615628914e-17 # FAIL

$ raku -e 'say 0.7 - 0.6 - 0.1'
0 # CORRECT!

As a bonus it also handles big nums out of the box. Worth trying.

Jeeva Ramanathan • Nov 21 '23

Interesting! Thanks for adding

Lev N. • Nov 17 '23 • Edited

Great article and solution for an issue not a lot of modern programmers know about (especially problematic when dealing with finances). Just one thing - I thought it is worth mentioning that .toFixed() in Javascript is a purely cosmetic method, it should only be used for display purposes since (like you mentioned) it returns the string representation of the decimal.

Jeeva Ramanathan • Nov 21 '23

Thanks for your comment! You're correct that .toFixed() is like a cosmetic method as it only affects the way the number is displayed, not its actual value.

tq-bit • Nov 17 '23

I didn't know.toPrecision before. Thanks for sharing, you wrote a great article there

Jeeva Ramanathan • Nov 21 '23

Thanks! Glad this helped you discover toPrecision().

Mike Stemle • Nov 17 '23

Well done, friend.

Jeeva Ramanathan • Nov 21 '23

Thanks, friend!

An Võ • Nov 17 '23

Jeeva Ramanathan • Nov 21 '23 • Edited

🙌🏻

Hassan • Nov 19 '23

That was so awesome :)

Jeeva Ramanathan • Nov 21 '23

Thank you for your feedback.

CitronBrick • Nov 17 '23

You can enable syntax highlighting in Dev.to using

triple_backtick javascript
code
triple_backtick

Jeeva Ramanathan • Nov 21 '23

Yeah, Sure🙌🏻

Samir • Nov 19 '23

One of the best in-depth technical articles I've read so far. I'm sure not many JS enthusiasts will read this or even care about the intricacies of it So I'm lucky to have read it!
Is it just JavaScript or other languages also use the same IEEE 754 standard?

Jeeva Ramanathan • Nov 21 '23 • Edited

Glad to hear that!
The IEEE 754 standard is not exclusive to JavaScript; Many programming languages like Java, Python etc., use this standard for representing floating-point numbers.

Samir • Nov 28 '23

Surprising! I tried this exact same expression on Java, Rust, Python and all of them yielded the same results.
I suppose they all have their own libraries to deal with this inconsistency.
Also, do you know that JavaScript loses number precision after like 18 digits? Could this be the same reason? Or are there different causes for that?