I would hate if this became the only numeric type available in JS (in fact, I don't want it at all), but it's dishonest to quote "specification" as you have and then dismiss it as such, as it doesn't claim to be one, the word doesn't appear a single time in it, and if you go through to the github repo, the readme explicitly refers to the page as a "descriptive web page".
In fact, the only line of actual substance in your post is "For example, rounding modes and overflow behavior are not addressed", and it turns out that's only true for the descriptive web page, not the reference implementation.
> I imagine this project is inspired by the sad state of numerical computing in Javascript, but this proposal will surely only make it worse. The world certainly doesn't need a new, incompatible, poorly-thought-out floating point format.
I'll just quote pg here:
Yeah, we know that. But is that the most interesting thing one can say about this article? Is it not at least a source of ideas for things to investigate further?
The problem with the middlebrow dismissal is that it's a magnet for upvotes. The "U R a fag"s get downvoted and end up at the bottom of the page where they cause little trouble. But this sort of comment rises to the top. Things have now gotten to the stage where I flinch slightly as I click on the "comments" link, bracing myself for the dismissive comment I know will be waiting for me at the top of the page.
This format is suicide from a numerical stability POV. It will lose 3 to 4 bits of precision for an operation with mixed exponents, whereas double will only lose one. Any kind of marginally stable problem, say eigenvalues with poorly conditioned data, will yield crap.
From my own understanding, an operation will lose precision iff () the result cannot be represented with 52 significant coefficient bits. Logically, the same happens in IEEE754, the difference is that the loss of precision in DEC64 is always a multiple 3.5 bits, whereas IEEE754 can lose precision in decrements of one bit.
() Maybe excluding over/underflow scenarios.
To clarify, what you say sounds like (I'm pretty sure that's not what you meant) every operation with mixed exponent will lead to loss of precision. From my understanding, that is not the case. It also sounds like every IEEE754 operation with mixed exponents only leads to one bit precision loss while it could lead to much more (in fact to (<total number of fraction bits between the two IEEE754 doubles> - 52).
OK. It looks like the proposed representation represents numbers as a signed 56 bit integer times ten to a signed 8-bit number. That does avoid fiddling with BCD, but it's VERY different from usual floating point. Look at the neighborhood of zero. As with usual floating point there's a gap between zero and the smallest nonzero number... but unlike floating point numbers, the next larger nonzero number is twice the smallest nonzero number. The behavior of numerical methods in DEC64 will, I suspect, be quite different from that of floating point. It would be very interesting to know what the difference is, and I'd hope that proponents of it as "the only number type in the next generation of application programming languages" would exercise due diligence in that and other regards.
I completely accept and agree with your criticism of my criticism.
My gut sense is that this proposal is simply too amateurish to be worth the effort of thoroughly debunking. Floating point is kind of like cryptography: the pitfalls are subtle and the consequences of getting it wrong are severe (rockets crashing, etc). Leave it to the experts. This is not a domain where you want to "roll your own."
In fact, the only line of actual substance in your post is "For example, rounding modes and overflow behavior are not addressed", and it turns out that's only true for the descriptive web page, not the reference implementation.
> I imagine this project is inspired by the sad state of numerical computing in Javascript, but this proposal will surely only make it worse. The world certainly doesn't need a new, incompatible, poorly-thought-out floating point format.
I'll just quote pg here:
Yeah, we know that. But is that the most interesting thing one can say about this article? Is it not at least a source of ideas for things to investigate further?
The problem with the middlebrow dismissal is that it's a magnet for upvotes. The "U R a fag"s get downvoted and end up at the bottom of the page where they cause little trouble. But this sort of comment rises to the top. Things have now gotten to the stage where I flinch slightly as I click on the "comments" link, bracing myself for the dismissive comment I know will be waiting for me at the top of the page.