25 Numerics library [numerics]

25.8 Mathematical functions for floating-point types [c.math]

25.8.4 Classification / comparison functions [c.math.fpclass]

The classification / comparison functions behave the same as the C macros with the corresponding names defined in the C standard library.
Each function is overloaded for the three floating-point types.
See also: ISO C 7.12.3, 7.12.4