Are 40-bit integers represented exactly in JavaScript?

Question

I'm using a server-side calculation which needs to generate (with * and + operations) and compare 40-bit integers. I'm aware that at that point the V8 engine stores the numbers as Double rather than int. Can I rely on these numbers to be generated and compared correctly?

My intuition says yes - doubles shouldn't have trouble with that - but I'm not sure how to check or where to find information on this.

Answer 1

Yes.

A JavaScript Number, which is a 64-bit IEEE 754 floating point value, can store integers from -2⁵³ to 2⁵³ without loss of precision, since doubles can store up to 53 bits of mantissa (52 explictly).

References:

• ECMA-262: 4.3.19 Number value

• Double-precision floating point numbers (Wikipedia)