https://cygwin.com/pipermail/cygwin-talk/2005q1/000345.html
gcc-3.3.3 :fpclassify
gcc
https://docs.oracle.com/cd/E88353_01/html/E37846/fpclassify-3m.html
fpclassify - man pages section 3: Extended Library Functions, Volume 2
fpclassify - classify real floating type The fpclassify() macro classifies its argument value as NaN, infinite, normal, subnormal, or zero. First, an argument...
man pagesextended librarysectionfunctionsvolume
https://inbox.sourceware.org/glibc-cvs/20220609132226.74D5B38344E6@sourceware.org/t/
[glibc/azanella/clang] math: Do not use __builtin_fpclassify on clang
do not useglibcclangmathbuiltin