(PHP 4 >= 4.2.0, PHP 5, PHP 7, PHP 8)
is_infinite — Finds whether a value is infinite
$num): bool
   Returns true if num is infinite (positive or 
   negative), like the result of log(0) or any value too 
   big to fit into a float on this platform.
  
numThe value to check
   true if num is infinite, else false.