CODEWITHSUNDEEP
javascriptintegerunsigned-integer
user1367401
user1367401

Reputation: 1050

Unsigned 32 bit integers in Javascript

How can I emulate 32bit unsiged integers without any external dependencies in Javascript? Tricks with x >>> 0 or x | 0 don't work (for multiplication, they seem to work for addition / subtraction), and doubles lose precision during multiplication.

For example, try to multiply 2654435769 * 340573321 (mod 2^32). The result should be 1.

This answer has multiplication. What about addition / subtraction / division?

Here's a link to wolfram alpha, presenting the equation above.

Upvotes: 9

Views: 9237

Answers (2)

mseddon
mseddon

Reputation: 1885

You can ape it with BigInts in 2020.

const u32mul = (x, y) => Number((BigInt(x) * BigInt(y)) & 0xFFFFFFFFn);

A sufficiently smart compiler should work this out, but I haven't benchmarked this, so proceed with caution.

The other alternative would of course drop into WebAssembly. If you need to be working at this level, I'd strongly advise it.

Upvotes: 1

ephemient
ephemient

Reputation: 204718

A 32-bit unsigned int fits within Javascript's 64-bit float -- there should be no loss of precision when performing addition, subtraction, or division. Just mask with 0xffffffff to stay within a 32-bit integer. Multiplication goes beyond what fits, but you already have a solution for that.

Upvotes: 3

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