Why is 0.1 + 0.2 returns 0.30000000000000004 in JavaScript?
Why is 0.1 + 0.2 returns 0.30000000000000004 in JavaScript?
Have you performed simple arithmetic operations like 0.1 + 0.2? You might have gotten something strange: 0.1 + 0.2 = 0.30000000000000004.
Ugh, i thought this was a question, not a link. So i spent time googling for a good tutorial on floats (because I didn't click the link)....
Now i hate myself, and this post.
A good way to think of it is to compare something similar in decimal. .1 and .2 are precise values in decimal, but can't be represented as perfectly in binary. 1/3 might be a pretty good similar-enough example. With a lack of precision, that might become 0.33333333, which when added in the expression 1/3 + 1/3 + 1/3 will give you 0.99999999, instead of the correct answer of 1.
Python has no issues representing
1/3 + 1/3 + 1/3as 1. I just opened a python interpreter, imported absolutely no libraries and typed
1/3 + 1/3 + 1/3enter and got 1 as the result. Seems like if python could do that, JavaScript should be able to as well.I thought it was a rather simple analogue, but I guess it was too complicated for some?
I said nothing about JavaScript or Python or any other language with my 1/3 example. I wasn't even talking about binary. It was an example of something that might be problematic if you added numbers in an imprecise way in decimal, the same way binary floating point fails to accurately represent 1/10 + 1/5 from the OP.
That’s because the nearest representable float to 0.99999999999999 is 1.0 - not because Python is handling rationals correctly.
This is a float imprecision issue that just happens to work out in this case.
It’s worth wondering why, if Python is OK with “/“ producing a result of a different type than its arguments, don’t they implement a ratio type. e.g. https://www.cs.cmu.edu/Groups/AI/html/cltl/clm/node18.html#SECTION00612000000000000000
It's how CPUs do floating point calculations. It's not just javascript. Long story short, a float is stored in the format of one bit for the +/-, some bits for a base value (mantissa), and some bits for the exponent. As a result, some numbers aren't quite representable exactly.
JavaScript is truly a bizarre language - we don’t need to go as far as arbitrary-precision decimal, it does not even feature integers.
I have to wonder why it ever makes the cut as a backend language.