Arithmetic function `isinfinite` missing?

[dnewhall]

The man page says isinfinite is one of the predefined arithmetic functions, but when I go and test it:

$ echo $(( isinfinite(inf) ))
ksh: isinfinite(inf) : unknown function

isinf(inf) works as expected, though.

Was this removed and the documentation needs to be updated? Should it be in there and no one noticed it was missing until now?

[McDutchie]

As the manual page says: “Any of the following math library functions that are in the C math library can be used within an arithmetic expression:”, etc.

What functions are in the C math library depends on the operating system. Your system has isinf but not isinfinite (as does mine; I don't know on what systems isinfinite exists). Both are checked for at compile time in math.tab, which is parsed by math.sh, which is executed by iffe.

[dnewhall]

Should Ksh make some guarantees here? They are really useful, but if they are platform-defined it makes any shell script that uses them inherently non-portable.

I just found out this is a big issue with fpclassify, which cannot be portably used at all in its current state (fpclassify(nan) returns 0 on Linux, 1 on MacOS, and 2 on FreeBSD...)