[% setvar title Standardise Handling Of Abnormal Numbers Like Infinities And NaNs %]

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Standardise Handling Of Abnormal Numbers Like Infinities And NaNs


  Maintainer: Jarkko Hietaniemi <jhi@iki.fi>
  Date: 5 Aug 2000
  Mailing List: perl6-internals@perl.org
  Number: 38
  Version: 2
  Status: Developing


The handling of various abnormal numeric entities like infinities (positive, negative), not-a-numbers (NaNs, various kinds of those, signaling, non-signaling), epsilons (positive and negative) is left to the native math libraries. A more concerted effort to standardise the behaviour of Perl across platforms would be desirable.


The abstract pretty much took care of it.


In an SV have bits that mark whether the numeric aspect of the scalar is abnormal and if so, what kind of abnormality are we dealing with. The Perl math operations have to watch out for those bits and do The Right Thing before the native math ops kick in, so that for example infinity + anything-but-nan = infinity, anything + nan = nan, and so on.

Watching out for the abnormality bits may be a performance hit. If so, it may be possible during the configuration phase probe how well the native math semantics obey the semantics we define for Perl, and let the native math take care of where it and us agree.

mjd quoth:

	If Perl supported bignums as a native scalar type, then
	handling of nans and infinities would come out of that naturally.

	Supporting bignums in Perl would insulate users from details
	of integer and float size on native platforms and would
	improve portability of Perl programs.

	Programs would be more robust.  Instead of failing
	mysteriously when a number overflowed, they would continue to
	work properly.
	Prior art:  Lisp.


	PDL::Math [suggested by Tim Jenness]
	p6rfc for bigints [to be written]