| -----Original Message----- | From: boost-bounces@lists.boost.org | [mailto:boost-bounces@lists.boost.org] On Behalf Of Johan Råde | Sent: 02 August 2006 09:44 | To: boost@lists.boost.org | Subject: Re: [boost] [serialization] facets for non-finite numbers | | | | > Johan Råde wrote: | > | I note that: | > | | > | The output from the extended_num_put facet is consistent | > | with the C99 | > | standard, except that I do not put signs on NaNs. I | will not change | > | that, since there is no reasonable way for a C++ program to | > | detect that sign. | | Paul A. Bristow wrote: | | > Surely C99 signbit tests the sign bit? (And is best used | for testing the | > sign of infinity?) | > | > | (And the sign has no meaning anyway, unlike infinity | > | where a sign sometimes, but not always, does have meaning.) | > | > Mathematically, you are absolutely correct, but I have argued, | > and continue to argue strongly, that there really IS a sign bit, | > and that it is unnecessary, indeed wasteful, | > to prevent users from making some entirely private use | > of this potentially precious sign bit, | > when it costs almost nothing to simply output a '-' if the | NaN has the sign | > bit set. | | You are right, but our goals are different. You are working on a | proposal to the C++ standardization committee. I writing code that | should work with existing C++ compilers and std lib | implementations. So I can not assume that the C99 signbit macro is present. OK, so why not write - or get someone else to write ;-) a C++ is_negative function, and use the signbit macro if available, or make up your own bit test if not? There are a few variations with type, endianness and compiler, of course, but not TOO many? | What do you thing of Robert Ramey's idea of making it possible to | configure a stream to report an error when a non-finite number is | inserted or extracted? This could be done with a new stream flag and | corresponding manipulators. Some check would seem extremely wise, or archives may later prove unreadable :-(( But I am uncertain how best to do it. Paul --- Paul A Bristow Prizet Farmhouse, Kendal, Cumbria UK LA8 8AB +44 1539561830 & SMS, Mobile +44 7714 330204 & SMS pbristow@hetp.u-net.com