Convert to a KIND=4 integer type, which is the same size as a C long integer. This is equivalent to the standard INT intrinsic with an optional argument of KIND=4, and is only included for backwards compatibility. 
GNU extension
Elemental function
RESULT = LONG(A) 
| A | Shall be of type INTEGER,REAL, orCOMPLEX. | 
The return value is a INTEGER(4) variable. 
    © Free Software Foundation
Licensed under the GNU Free Documentation License, Version 1.3.
    https://gcc.gnu.org/onlinedocs/gcc-10.2.0/gfortran/LONG.html