| -----Original Message----- | From: boost-bounces@lists.boost.org | [mailto:boost-bounces@lists.boost.org] On Behalf Of Caleb Epstein | Sent: 17 March 2006 15:13 | To: boost@lists.boost.org | Subject: Re: [boost] [serialization] | Serialisation/deserialisationoffloating-point values | | On 3/17/06, Paul A Bristow <pbristow@hetp.u-net.com> wrote: | > | > Ooops - this is a typo. | > | > It should of course be 3010/10000. | | Which is one of the reasons magic numbers in code are best avoided. Touche! Case proven! | It sure would be nice if one could just use | numeric_limits<T>::digits10 + 2 instead | of numeric_limits<T>::digits * 3010 / 10000, but the former gives a | different result for float (8 instead of 9). | | Perhaps this cryptic calculation might be best addressed by a | boost::numeric_limits<T> which could extend std::numeric_limits<T> and | include Paul Bristow's proposed max_digits10 (see | http://www2.open-std.org/JTC1/SC22/WG21/docs/papers/2005/n1822.pdf)? Well this would be faster than the glacial speed of simple no-brain changes like this to Standards. And while we are at it, the macros I proposed to WG14 for C could also be added, in case these are more convenient for (C++ AND C) users. http://www2.open-std.org/JTC1/SC22/WG14/www/docs/n1151.pdf Date: 2005-11-30, version 1 For example: #define FLT_MAXDIG10 (2+(FLT_MANT_DIG * 3010)/10000) #define DBL_MAXDIG10 (2+ (DBL_MANT_DIG * 3010)/10000) #define LDBL_MAXDIG10 (2+ (LDBL_MANT_DIG * 3010)/10000) which yield the following values on typical implementations: FLT_DIG 6, FLT_MAXDIG10 9 DBL_DIG 15, DBL_MAXDIG10 17 LDBL_DIG 19, LDBL_MAXDIG10 21 Should it go into boost/detail/limits.hpp? I don't feel qualfied to do this, but it is long overdue to sort out this trivial problem. (and get on with the much more important problem of failure of round-tripping of all uses of stringstream, crucially lexical_cast and serialization). Paul -- Paul A Bristow Prizet Farmhouse, Kendal, Cumbria UK LA8 8AB Phone and SMS text +44 1539 561830, Mobile and SMS text +44 7714 330204 mailto: pbristow@hetp.u-net.com http://www.hetp.u-net.com/index.html http://www.hetp.u-net.com/Paul%20A%20Bristow%20info.html