On Fri, Dec 02, 2005 at 12:22:22PM -0000, John Maddock wrote:
Yep: the formats are mostly well known and the bit twiddling isn't that hard once you know what the format is, but there's at least one problem case: long double's on Darwin. I can't find any information on these after a quick google search, but I believe they're effectively a sum of two doubles. If so this is exceptionally bad form because it violates the most fundamental principal of IEEE arithmatic that a number is n*2^k. (Background: epsilon is very small for this type, it's possible to add a number "delta" to 1.0L and still get a distict value when "delta" is much smaller than the number of bit's in a long double would otherwise indicate. This makes a *lot* of IEEE based reasoning invalid. If anyone has more information on this type I'd appreciate a reference).
I don't have any first hand experience with Darwin's long double, but what you wrote above seems correct according to <url:http://tinyurl.com/9thr3> (<url:http://gcc.gnu.org/viewcvs/trunk/gcc/config/rs6000/darwin-ldouble-format?rev=85371&view=markup>) Regards Christoph -- http://www.informatik.tu-darmstadt.de/TI/Mitarbeiter/cludwig.html LiDIA: http://www.informatik.tu-darmstadt.de/TI/LiDIA/Welcome.html