Why decimal?

Erik Corry erik.corry at gmail.com
Wed Jun 24 10:59:10 PDT 2009


2009/6/23 Brendan Eich <brendan at mozilla.com>

> On Jun 23, 2009, at 12:18 AM, Christian Plesner Hansen wrote:
>
> I've been looking around on the web for reasons why decimal arithmetic
> should be added to ES.  The most extensive page I could find was
> http://speleotrove.com/decimal/decifaq.html.  If anyone know other
> good sources of information about decimal and its inclusion in ES
> please follow up.
>
>
> Mike Cowlishaw's pages on decimal have lots of arguments for it:
>
> http://www2.hursley.ibm.com/decimal/decifaq.html
> http://www2.hursley.ibm.com/decimal/
>

I'm afraid both these links seem to have broken.


> <http://www2.hursley.ibm.com/decimal/>
>
> The most-duplicated JS bug in bugzilla.mozilla.org is
>
> https://bugzilla.mozilla.org/show_bug.cgi?id=5856
>
> Here's a typical naive JS user complaining that his computer his broken
> because it can't calculate correct differences:
>
> "... I typed in:
>
> 9533.24-215.10
>
> … and here is the garbage Apple babbled back at me: 9318.139999999999"
>
> He blamed Apple. Naive users often blame hardware for software bugs.
>
>
> The strongest argument seems to be financial: binary arithmetic is
> approximate in a way that makes it unsuitable for financial
> calculations.  I buy this argument in general -- I would definitely
> want my bank to use some form of decimal arithmetic rather than binary
> -- but less so in the context of ES.
>
>
> Do you consider that naive user's calculator example to be "financial"? I
> do not.
>
> The problem is worse for non-experts. The experts can cope.
>
> Anyway, decimal is not being pushed into JS at this point. At the last
> face-to-face TC39 meeting, we changed direction to explore generalizing
> value type support (including operators and literals if we can) so that
> libraries could add first class number-like types.
>
> Whether any new value type would be native or self-hosted, and whether it
> would be included in the core standard, are issues we want to defer until
> later, ideally until there are de-facto standards to codify.
>
> The counter-argument articulated at the meeting by Sam was that it's rare
> for users to download binary extensions to JS for browsers (Flash is the
> only exception, and it's not primarily a JS extension). So users won't get
> decimal unless it is part of the normative core spec, so the usability bug
> reported as Mozilla bug 5856 won't get fixed.
>
> I think Sam has a point; lack of a standard could be a problem. But
> whatever we do about it, the committee agreed to work on value types first.
> They're on the Harmony agenda.
>
> /be
>
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