I have a buddy at US Fish and Wildlife where they do river flow modeling with Fortran routines from the seventies formerly compiled on Windows machines. He was finding it increasingly difficult to get his all-powerful shadowy IT division to install a compliant MS Fortran compiler, and linux (somehow deemed governmentally untenable?) was out of the question. So i helped him get his ~2000 Fortran lines into C/C++. woowee... but did i see some hairy spaghetti code. A favorite maneuver was to jump out of a loop, change the loop counter on a subroutine branch, and jump back into the middle of the loop.
To elaborate: When people mention that supercomputing relies on Fortran code because it runs faster, that's primarily because the compiler knows the program can't modify a loop counter. So an optimizer can shovel off big arrays to array processors (1970s), GPUs (now), registers, etc, and do parallel or superscalar computation.
The FOR loop become a hint that tells the compiler it can take extraordinary measures on the nested instructions.
You could do the same thing in C if you use compiler directives, or in other languages like Pascal, but there's a critical mass of Fortran code, so that's where vendors put the effort.
It's been many years, but I seem to remember porting the NCAR Graphics Package written in FORTRAN IV to FORTRAN 77 on a Data General MV series box.
If memory serves, they had a trick to create simulated pointers, by declaring a one element array somewhere in memory, and then indexing way outside of its bounds in order to point into other areas of memory.
I don't remember the details, but I seem to remember there was a statement ("EQUIVALENCE"?) that facilitated this magic.
This was from code originally from about 1978ish, which compiled on a Microsoft Fortran compiler from the 2000s. It looked something like (without indents):
DO I=1,10000
...
IF (QQQ .LT. RIX70) THEN
CALL IXNARF( I, J, R1, R7, XL23 )
GOTO 23
...
END IF
111 CONTINUE
...
END
IXNARF could change 'I' (because Fortran 77 passed arguments by reference not value) and sometime after line (er... "card") 23 it might jump back into the loop at 111.
oh and there was like three comments in the whole several thousand lines, including my favorite at the top of one of the main loops:
> Change the loop counter? That's supposed to be impossible in Fortran, isn't it?
It is impossible inside the loop, even in F77.
But if a global variable is used as a loop counter, and the variable is altered in a subroutine, then the code altering the variable is not inside the loop. At least not in the eyes of the Fortran compiler.
$ cat test.f08
program test
integer i
do i = 1,3
call sub
print *,i
end do
contains
subroutine sub
i = 3
end subroutine sub
end program test
$ gfortran --std=f2008 test.f08
$ ./a.out
3
There is no "standard" compiler. There is a Fortran standard, and there are standard-conforming compilers and standard-conforming programs.
There are popular compilers, like gfortran and the Intel compiler.
My point had nothing to do with popularity. My point is that non-standard-conforming programs can have anything happen when they execute, including starting World War III (see https://www.google.com/search?q=fortran+"start+world+war"), and showing output from one compiler doesn't prove anything.
there is one in ocean sciences. I don't remember which one although if you are really interested I can find out. Somebody translated it into C as part of their phd.
All fluid modeling at least. I once worked for a company that built heat exchanger simulations. I spent limited time in Fortran but was able to successfully integrate some C++ and C# libraries. The language isn't bad at all.
