On Sun, Dec 29, 2019 at 11:21:51PM -0500, David Mertz wrote: > Has anyone actually ever used those available bits for the zillions of NaNs > for anything good?
Absolutely. Back in the 1980s, Apple released one of the first (if not the first) IEEE-754 compliant maths library: SANE, the Standard Apple Numerics Environment. SANE used the NAN payload to encode diagnostic information on the kind of failure. For example, a payload of 1 was an invalid sqrt; a payload of 17 was an invalid string to float conversion; a payload of 34 was an invalid argument to an inverse trig function. I can tell you from personal experience that this was quite useful although not a panacea. For 64-bit floats, there are 51 bits available for the NAN payload. That's enough for a seven ASCII character message, or to encode (say) a 7 bit error code and 44 bits for a line number, or whatever information you need to allow the compiler to identify the source of the error. Javascript does a horrible/awesome (choose one) hack called "NAN boxing": https://anniecherkaev.com/the-secret-life-of-nan There's at least one Ada project that encodes tagged data in NANs: http://dan.corlan.net/software/nan_payload/ Unfortunately, indifferent support for NAN payloads by many compilers and languages has lead to developers neglecting NAN payloads, and lack of developer use for payloads leads to poor compiler support. -- Steven _______________________________________________ Python-ideas mailing list -- python-ideas@python.org To unsubscribe send an email to python-ideas-le...@python.org https://mail.python.org/mailman3/lists/python-ideas.python.org/ Message archived at https://mail.python.org/archives/list/python-ideas@python.org/message/73M3Q6Q2KB7CB5GYUHSCZPB3ANAGPPVW/ Code of Conduct: http://python.org/psf/codeofconduct/
