Two interoperable implementations rule

Mike Cowlishaw MFC at
Mon Jul 14 13:37:23 PDT 2008

> On Fri, Jul 11, 2008 at 7:10 PM, Maciej Stachowiak <mjs at> 
> > This may be tricky to define, since many possible
> > candidate implementations are open source and developed
> > collaboratively by community contributors and overlapping sets of
> > vendors. For example, would Rhino and SpiderMonkey count as
> > sufficiently independent implementations?
> Similarly, if we end up with, f.e., both WebKit and Spidermonkey using
> decNumber as our internal implementation of Decimal, does that count
> as two interoperable implementations?  It seems like we'd be at risk
> of mostly testing that code against itself, so I would hope that we
> look for such reuse cases when we're making sure that we actually have
> usefully-distinct implementations of features to validate the spec.

<chuckle>  Isn't that the idea of open-source software -- that by using 
the same software you get the same results (fdlibm, for example)?  But a 
good point .. the 'new' issue here is that the same code in the different 
environments ends up with the same calls to the underlying library and 
yields the same results. 

(The decNumber code is quite stable, for example -- averaging fewer than 
one detected bug/year since its first release in 2001, is used in numerous 
IBM, SAP, and other vendors' products, and is part of the verification 
suite for, PowerPC, and IBM mainframe hardware.)


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