doppio sounds awesome. from the paper:

Numeric support. Direct support for 64-bit integers would enable languages to efficiently represent a broader range of numeric types in the browser. The DOPPIOJVM uses a comprehensive software implementation of 64-bit integers to bring the long data type into the browser, but it is extremely slow when compared to normal numeric operations in JavaScript.

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how far is this from being solved?

Thanks! I hope Doppio can become useful to many more people. :)

There is a proposal for value types [0] that Niko Matsakis [1] and Brendan Eich [2] talked about a couple of years back and could be used to implement 64-bit numbers in JS, but I'm still waiting for an implementation or a more complete proposal. Looks like it might be dead in the water, as the proposal hasn't been edited in quite some time, but I do not have my finger on the pulse of browser standards so I could be wrong.

[0] http://wiki.ecmascript.org/doku.php?id=strawman:value_object...

[1] http://smallcultfollowing.com/babysteps/blog/2014/04/01/valu...

[2] http://www.slideshare.net/BrendanEich/value-objects

You could use (the compiled and optimized version of) the implementation we have in Scala.js: https://github.com/scala-js/scala-js/blob/master/library/src... It is significantly faster, especially for arithmetic operations, and dramatically so for division, remainder, as well as `toString()` (up to 100x speedup). It also contains the unsigned variant of operations (for java.lang.Lond.divideUnsigned for instance).

Oh, nice! I'll take a look at that when I next get the chance. I assumed that Closure's Long library, which is based on GWT's Long implementation, would be well-optimized, and never looked into an alternative.