Good. The code below works for me - and I will advise any problems I encounter. http://http.cs.berkley.edu/~wkahan/ieee754status/ieee754.ps is about the number of decimal places. The formula below generates the values W Kahan, of IEEE754 fame, gives (for example 17 for 64-bit double). To amplify my reply to Vicotr Wagner, the following example showing the effect of a few least significant bit changes and that you need precision 17 to show this reliably. double d = 1.; for (int i = 1; i < 10; i++) { d = _nextafter(d, +999.); // increment least siginificant bit. cout << i << ' ' << setw(20) << setprecision(15) << d << ' '<< setw(20) << setprecision(16) << setw(20)<< d << ' ' << setprecision(17) << d << endl; } Outputs bits changed precision 15 precision 16 precision 17 1 1 1 1.0000000000000002 2 1 1 1.0000000000000004 3 1 1.000000000000001 1.0000000000000007 4 1 1.000000000000001 1.0000000000000009 5 1 1.000000000000001 1.0000000000000011 6 1 1.000000000000001 1.0000000000000013 7 1 1.000000000000002 1.0000000000000016 8 1 1.000000000000002 1.0000000000000018 9 1 1.000000000000002 1.000000000000002 However, I note that this involves lots of calls to ostr.precision() and perhaps it can be don't more efficiently by a single call when ostream just after constructed. But it works and the cost is small. Paul | -----Original Message----- | From: boost-bounces@lists.boost.org | [mailto:boost-bounces@lists.boost.org] On Behalf Of Gennadiy Rozental | Sent: 27 July 2004 07:12 | To: boost@lists.boost.org | Subject: [boost] Re: Unit test could usefully output more | significant digitstolog files? | | > template<typename T> | > struct print_log_value { | > void operator()( std::ostream& ostr, T const& t ) | > { | > if(std::numeric_limits<T>::is_specialized && | > std::numeric_limits<T>::radix == 2) | > { // Show all possibly significant digits (for example, | 17 for 64-bit | > double). | > ostr.precision(2 + std::numeric_limits<T>::digits * 301/1000); | > } | > ostr << t; // by default print the value. | > } | > }; | | | Actually it's in my TODO list. | | I consider using this solution after release. | | Gennadiy. | | | | _______________________________________________ | Unsubscribe & other changes: | http://lists.boost.org/mailman/listinfo.cgi/boost | |