NAME
isinf, isnan - test for infinity or not-a-number ()

SYNOPSIS
int isinf(x) double x;
int isnan(x) double x; The function returns 1 if the number is
(plus or minus) infinity, otherwise 0. The function returns 1 if
the number is a ‘NaN’ (Not-a-Number), otherwise 0. math(3)
"IEEE Standard for Binary Floating-Point Arithmetic", ANSI, Std
754-1985.