CODEWITHSUNDEEP
javascriptmathoverflow
Art
Art

Reputation: 24607

JavaScript integer overflow

The following code 

console.log(Math.pow(2, 53)); 
console.log(Math.pow(2, 53) + 1);

produces exactly same output for both calculations:

9007199254740992

Why?

Upvotes: 6

Views: 2627

Answers (2)

Jonathan Leffler
Jonathan Leffler

Reputation: 755010

The result you see occurs because Math.Pow() is working with floating point numbers, and when you reach the 16th decimal digit, you can't necessarily add one to the least significant decimal digit of the value and expect the result to change.

There are typically, in a 64-bit (8-byte) IEEE 754 floating-point binary value, 53 bits for the mantissa (including the implied 1-bit). Your calculation Math.Pow(2, 53) requires 54 bits in the mantissa to be guaranteed of a change. If you add 2, you should see the change.

Upvotes: 11

ponce
ponce

Reputation: 919

All Javascript numbers are double.

Upvotes: -3

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