At tonight’s SG10 meeting, I was asked to provide the document number of the Committee Draft of what became the Mathematical Special Functions Int’l Standard. That paper was N2850, and is available via http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n2850.pdf.

It is Clause 5.1 of that document that specifies the equivalent of a feature test macro as it was understood in 2009.

Best,

— WEB