See the FAQ: How to do a minimal reproducible example reprex
for beginners. The code provided does not compile under gfortran
due to an error on the first line and the absence of PORTLIB
on the second. Because it won't compile, it can't be converted with f2c
to C
to see what it does. The alternative (for me at least) is turning the calendar back to 1966 and learn FORTRAN all over again.
Besides
GOTO considered harmful
@nirgrahamuk 's link is also what I'd recommend doing with FORTRAN source code.