ECMAScript Version 5 Approved

systembug writes "After 10 years of waiting and some infighting, ECMAScript version 5 is finally out, approved by 19 of the 21 members of the ECMA Technical Committee 39. JSON is in; Intel and IBM dissented. IBM is obviously in disagreement with the decision against IEEE 754r, a floating point format for correct, but slow representation of decimal numbers, despite pleas by Yahoo's Douglas Crockford." (About 754r, Crockford says "It was rejected by ES4 and by ES3.1 — it was one of the few things that we could agree on. We all agreed that the IBM proposal should not go in.")

Comments

use fixed point instead

[StripedCow]

instead of using floating point for representing decimal numbers, one can of coarse easily use fixed point... for currency computations, just store every value multiplied by 100 and use some fancy printing routine to put the decimal point at the right position.

and if you're afraid that you might mix up floating point and fixed point numbers, just define a special type for the fixed-point numbers, and define corresponding overloaded operators... oh wait

I can guess why IBM was pushing for IEEE 754r

[tjwhaynes]

The debate over floating point numbers in ECMAScript is interesting. IEEE 754 has plenty of pitfalls for the unwary but it has one big advantage - it is directly supported by the Intel-compatible hardware that 99+% of desktop users are running. Switching to the IEEE 754r in ECMA Script would have meant a speed hit to the language on the Intel platform until Intel supports it in hardware. This is an area where IBM already has a hardware implementation of IEEE 754r - its available on the POWER6 platform and I believe that the z-Series also has a hardware implementation. I suspect that IBM will continue to push for IEEE 754r in ECMAScript, I wonder whether Intel is considering adding IEEE 754r support to its processors in the future.

Disclaimer: I have no contact with the IBM ECMAScript folks.

Cheers,
Toby Haynes

Re:I can guess why IBM was pushing for IEEE 754r

[teg]

IEEE 754 has plenty of pitfalls for the unwary but it has one big advantage - it is directly supported by the Intel-compatible hardware that 99+% of desktop users are running. Switching to the IEEE 754r in ECMA Script would have meant a speed hit to the language on the Intel platform until Intel supports it in hardware. This is an area where IBM already has a hardware implementation of IEEE 754r - its available on the POWER6 platform and I believe that the z-Series also has a hardware implementation.

ECMAScript is client side, so I don't think that was the issue. Z-series is server only, and POWER6 is almost all servers - and for POWER workstations, the ability to run javascript a little bit faster has almost zero value. The more likely explanation is that IBM has its roots in business, and puts more importance into correct decimal handling than companies with their roots in other areas where this didn't matter much.

Re:I can guess why IBM was pushing for IEEE 754r

[tjwhaynes]

Why do processors need decimal number support? 10 is just an arbitrary number humans picked because they happen to have 10 fingers. There's no connection between that and computers.

Clearly you've never dealt with an irate customer who has spent $$$ on your software product, has created a table using "REAL" (4-byte floating point) types and then wonders why the sums are screwing up. IEEE754 can't accurately represent most fractions in the way that humans do and this means that computers using IEEE 754 floating point give different answers to a human sitting down with pen and pencil and doing the same sums. As humans are often the consumer of the information that the computer spits out, making computers produce the correct results is important.

There are plenty of infinite precision computing libraries out there for software developers to use. However, they are all a lot slower than the 4, 8 or 10 byte floating point IEEE 754 calculations which are supported directly by the hardware. Implementing the IEEE 754r calculations directly on the CPU means that you can get close to the same performance levels. I'm guessing that at best, 128 bit IEEE 754r performs about half the speed of 64bit IEEE 754, purely because of the data width.

Cheers,
Toby Haynes

Re:I can guess why IBM was pushing for IEEE 754r

[tjwhaynes]

(...) I'm guessing that at best, 128 bit IEEE 754r performs about half the speed of 64bit IEEE 754, purely because of the data width.

According to Douglas Crockford "...it's literally hundreds of times slower than the current format.".

I don't doubt that the software implementations are "hundreds of times slower". I've had my hands deep into several implementations of decimal arithmetic and none of them are even remotely close to IEEE 754 in hardware. IEEE 754r is better than some of the predecessors because a software implementation can map the internal representation to integer maths. However, IEEE 754r does exist in hardware and I was guessing that the hardware IEEE 754r is still half the speed of hardware IEEE 754.

One other thing that IEEE 754 has going for it is the emerging GPU-as-co-processor field. The latest GPUs can do full 64bit IEEE 754 in the stream processors, making massive parallel floating point processing incredibly speedy.

Cheers,
Toby Haynes

Re:JSON is in!?

[maxume]

Implementations are expected to provide a safe(r) parser than eval.

Financial Calculations

[pavon]

When you have strict regulatory rules about how rounding must be done, and your numerical system can't even represent 0.2 exactly, then it is most certainly a concern. There are other solutions, such as using base-10 fixed point calculations rather than floating point, but having decimal floating point is certainly more convenient, and having a hardware implementation is much more efficient.

Re:JSON is in!?

[amicusNYCL]

Is that how JSON took hold? By being easy to parse using eval?

No, it took hold because it's Javascript's native object notation. And, as you can imagine, if you have a string of code you use eval to convert it. There are several JSON parsers which do some validation before using eval to ensure that it contains only an object definition and no statements. It would be nice if that validation was standardized and built-in.

they could have just used XML instead

Developers have a choice between XML and JSON (XML is already well supported), but many developers choose JSON instead of XML. Among other things, a JSON structure is typically smaller than a comparable XML structure, and when it's decoded you don't need to use anything special to use it.

instead of inventing a new serialized object format.

They didn't really invent this so much as realize that the native object format can easily be used to transfer arrays and objects between languages. It's very easy to create an associative array in PHP, encode it and send it to Javascript, and end up with virtually the exact same data structure in Javascript. Working with an associative array in PHP (or Javascript) is obviously a lot easier than working with an XML structure. Virtually any language you would use on a server has support for associative arrays or generic objects, so it makes a lot of sense to pass those structures around in a way where you lose no meaning and each language natively supports it.

Re:Will this allow us a FOSS alternative to Flash?

[snaz555]

Until we get a slick gui editor for javascript+svg animation, no.

In other words, we need GNU Ecmas.