This question already has answers here:
Understanding floating point problems
(4 answers)
Closed 11 months ago.
This page has a simple alert:
alert(185.3 + 12.37);
To me, that should equal 197.67
However, in the browsers I've tested (Chrome/Safari on OSX, FF on Win7) the answer is:
197.67000000000002
Why is that? Is this just a known bug or is there more to JavaScript addition than I realize?
javascript uses the double datatype, which can't, due to restricted binary places, express all decimal numbers accurately (not all numbers can be expressed with finite binary places). You can read more at wikipedia.
You should read this:
http://download.oracle.com/docs/cd/E19957-01/806-3568/ncg_goldberg.html
It's not a bug; it's just a well-known fact of floating point numbers for every language.
In binary, this is the infinitely repeating binary fraction 11000101.10(10101110000101000111) - which cannot be represented in a finite number of bits, so it is rounded to an approximation.
Related
This question already has answers here:
How to deal with floating point number precision in JavaScript?
(47 answers)
Closed last month.
I´ve come across this oddity when writing some JS code. It happens in both Chrome and Firefox:
10.04 + 0.01 = 10.049999999999999
Not sure if I´m just missing something obvious that causes this?
Right now I am handling it with rounding the number afterwards - Is there a better way to avoid this bug/feature?
This is a consequence of the way numbers are stored internally in IEEE 754 form.
To avoid this, use a BigDecimal library such as this one: https://www.npmjs.com/package/js-big-decimal
This question already has answers here:
Is floating point math broken?
(31 answers)
Closed 3 years ago.
I have big numbers coming from the backend service in my JS application. I don't want to lose any of the digits after the decimal place.
However, when a number like 999999999999999.99 is assigned to a variable in JS, it rounds it to 1000000000000000 and 99999999999999.99 turns to 99999999999999.98.
Both numbers are within the limits. i.e. less than Number.MAX_SAFE_INTEGER
See the above in action in the screenshot below:
Can anybody shed some light on it, please?
MAX_SAFE_INTEGER only guarantees precision for integers below it, not decimals.
In fact there are no decimals in Javascript only floating point numbers. When you try to represent a number with too much precision it'll just be rounded to the nearest 64 bit floating point number.
If you actually want decimals you will need to use a decimal library like decimal.js or you could write your own.
This question already has answers here:
Floating point inaccuracy examples
(7 answers)
Closed 7 years ago.
Today, I have seen strange issue with parseFloat in Javascript. When I an doing addition operation of the value I have seen some strange values, below are the examples:
parseFloat("31.099")+1;
Output:
32.099000000000004
Why do I have only problem with 31.099?
Floating numbers are always strange. Check out some descriptions in PHP Manual as well. There is a warning about precision.
Most of the programming languages do this, when you add an int to a floating number, it will make an approximation of the result. One work around would be to create your floating type and separate the floating value from the integer value.
Yes, floating point numbers are not always precise. It's because fractions cannot be precisely represented in binary.
To fix it, use toFixed() to round floating point numbers to the amount of precision you want. For example, for two decimal places:
num.toFixed(2)
This question already has answers here:
javascript large integer round because precision? (why?)
(2 answers)
Closed 8 years ago.
I've just run into a peculiar issue with Javascript.
An API call returns some JSON as it normally does. One of the ids returned is the long number "10151920335784069".
However, in Javascript world that becomes "10151920335784068" (one subtracted).
A quick test in the (Chrome) console demonstrates it:
x = 10151920335784069;
console.log(x);
10151920335784068
x==10151920335784069;
true
Further more:
x==10151920335784067;
true
x==10151920335784066;
false
What is going on here?
JavaScript (ECMA 262 5th Edition) uses double-precision 64bit numbers in IEEE 754 format. That representation cannot store your value in question exactly so it must round it to the nearest value per the IEEE 754 specification.
Authors and users of APIs that use JSON data should keep this limitation in mind. Many runtime environments (such as JavaScript) have potentially unexpected behavior regarding such numerical values even though the JSON format doesn't impose any such limitations.
All numerical variables in Javascript are stored as 64-bit floating point integers, so at high levels of precision, with numbers above 32 bits, it will round and give you slightly inaccurate numbers
If you want to check if two numbers are roughly even, you can use this
if(Math.abs(num-check)/check<1e-8)){
alert("For most practical intents and purposes, they are equal!");
}
This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
Is JavaScript's Math broken?
Any ideas as to why:
(872.23 + 2315.66 + 4361.16) == 7549.05
return false in a Javascript console (e.g. Chrome Developer console)?
If I try it with my calculator, the left side does exact 7549.05... However, Javascript displays it as 7549.049999999999. I could "fix" it or round it, or... but WHY should I be doing that for simple additions?
Thanks
Marco Mariani answered a similar question a short time ago:
What Every Computer Scientist Should Know About Floating Point Arithmetic
and the shorter, more to the point:
http://floating-point-gui.de/
That is not Javascript adding extra precision, that is your computer's floating-point representation not being able to accurately represent your number. Get around it by using rational numbers or fixed-point (instead of floating-point) arithmetic.
By using decimals, you are using floating point numbers. You would have to know a bit about how floating point is represented in binary form, and how binary floating point addition works to understand why adding floating point numbers does not always resolve to what you want.
Here is a quick google result that you might want to glance at: The Complete Javascript Number Reference
Also, if you want to learn how floating point is represented in binary look at IEEE floating point on Wikipedia.
Your best bet in this case would be to round.
This is because of how floats are represented in the hardware (32 bits, probably, but it's the same in any number of bits). Basically the issue is you can't represent something like "7549.05" exactly (more on this issue in wikipedia).
So, for practical uses, if the numbers are currency, a good option is multiplying by 100 so they are always integers, and operating with ints (which will give good results when adding, substracting or multiplying).