math - JavaScript not adding large numbers correctly (but getting very close) - Stack Overflow

admin管理员组

文章数量:1391047

I'm trying to add up a large number but it's not ing out correctly.

var searchSpace = 36;
var length = 11;
var binations = 0;

for(var i = 1; i <= length; i++) {
    binations += Math.pow(searchSpace, i);
}

The variable binations ends up being 135,382,323,952,046,190 which is not quite correct. It should be 135,382,323,952,046,196 (how is it off by 6?!) Any ideas?

I'm trying to add up a large number but it's not ing out correctly.

var searchSpace = 36;
var length = 11;
var binations = 0;

for(var i = 1; i <= length; i++) {
    binations += Math.pow(searchSpace, i);
}

The variable binations ends up being 135,382,323,952,046,190 which is not quite correct. It should be 135,382,323,952,046,196 (how is it off by 6?!) Any ideas?

• javascript
• math
• loops
• exponent

Share Improve this question Follow asked Jun 15, 2012 at 4:15 AaronAaron 10.9k1313 gold badges4040 silver badges5353 bronze badges 1

• 2 A good explanation of "Javascript doesn't have 'integers' - only floating point numbers": developer.mozilla/en/JavaScript/… – paulsm4 Commented Jun 15, 2012 at 4:21

Add a ment  | 

2 Answers 2

Sorted by: Reset to default 7

JavaScript uses IEEE-754 64-bit doubles as its number format. These cannot represent arbitrarily precise values; they bee incorrect when you exceed a certain threshold and begin instead storing values that are close to (but not quite exactly) the actual values. According to this earlier answer, the largest value that can be stored accurately is 2⁵³, which is about 9 × 10¹⁵. Your number (which is about 1.3 × 10¹⁷) is larger than this, so (with good probability) it cannot be represented accurately.

If you want to get the exact answer in JavaScript, you will need to use a library that supports arbitrary-precision integers. A quick Google search turned up this library, but I can't vouch for how accurate it is.

Hope this helps!

All numbers in Javascript are actually floating point numbers. You're dealing with very large numbers, and doing multiple manipulations on those numbers. The inherent errors in dealing with floats pile up quickly in this case, causing the "error".

Being off by 6 on a number that large is actually pretty good. You're off by only 0.000000000000004431%, roughly

本文标签： mathJavaScript not adding large numbers correctly (but getting very close)Stack Overflow