26 Feb 2022

Javascript Add (+) issue


My Client is explaining about minor javascript issue as we are working with cryptocurrencies:  (Replicated issue Link)

If I have 0.1 BTC in my first wallet and 0.2 BTC in my other wallet, I want to calculate the total using the javascript + (Add) feature.

Simply I am adding an array of all available wallets.

If I do, 0.1+0.2 = 0.30000000000000004 BTC

It should Show 0.30000000000000000 BTC liters overall!

What could be the solution to get an exact 0.3 BTC properly?


Find Fault here: codepen



27 Feb 2022

Best Answer

best answer

That error occurred because of the floating-point mechanism about how do they store values. That's why it feels like floating-point math is broken up!

If you check 0.1 + 0.2 == 0.3 
It will return false.
Reason: Neither 0.1 nor 0.2 are exactly representable in binary floating points logic. And nor is 0.3!
Binary floating points logic: The number is split into three parts, sign, exponent and fraction, when stored in binary.

You can see IEEE 754 Standards here on wikipedia.

When you write 0.1, it means 1/10. As per binary64 format,

The decimal value will become 0.100000000000000005551…
The hex float notation will become 0x1.999999999999ap-4

Always remember,

  • The more operations you do on a floating-point number / numbers, the more significant rounding errors can occur.


You can use round(number, k) and Ceiling Function for such decimal numbers, so you don't have to get BTC from your pocket. You can also use below equivalent logic too.

String myNumberString = String.format("%1.1d", Double.valueOf(myNumber));

Hope this helps you.

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