Daniel Krügler wrote:
To my opinion boost itself provides a simple helper class, namely static_log2, which allows the correct implementation by using the extended formular
#include <boost/integer/static_log2.hpp> .... std::size_t const length = (std::numeric_limits<T>::digits * boost::static_log2<std::numeric_limits<T >::radix>::value + std::numeric_limits<int>::digits - 1) / std::numeric_limits<int>::digits;
Note that the expression boost::static_log2<std::numeric_limits<T>::radix>::value is exactly 1 in the usual base-2 case, but e.g. 4 in case of base-16.
My proposed fix is exact in all cases, where radix is a power of 2, in other cases (like base-10) it would at least be a better approximation than the current one.
Thanks for letting me know, I need to think about this. It the radix isn't a power of 2, then I guess that frexp and ldexp will be slow and inaccurate. Maybe ldexp could be replaced with a multiplication. As it is, I'm not happy with the current implementation. It might be better to print the float to a string and then generate a hash value from that. That's not great, but it might be more portable. Daniel