CODEWITHSUNDEEP
fortranlegacygfortranintrinsics
Bob
Bob

Reputation: 253

What do I do about a FORTRAN intrinsic that was not part of the standard?

I'm trying to get a legacy FORTRAN code working by building it from source using gfortran. I have finally been able to build it successfully, but now I'm getting an out-of-bounds error when it runs. I used gdb and traced the error to a function that uses the loc() intrinsic. When I try to print the value of loc(ae), with ae being my integer value being passed, I get the error "No symbol "loc" in current context." I tried compiling with ifort 11.x and debugged with DDT and got the same error. To me, this means that the compiler knows nothing of the intrinsic.

A little reading revealed that the loc intrinsic wasn't part of the F77 standard, so maybe that's part of the problem. I posted the definition of the intrinsic below, but I don't know how I can implement that into my code so loc() can be used.

Any advice or am I misinterpreting my problem? Because both gfortran and ifort crash in the same place due to an out of bounds error, but the function utilizing loc() returns the same large number between both compilers. It seems a bit strange that loc() wouldn't be working if both compilers shoot back the same value for loc.

Usage:

iaddr = loc(obj)

Where:

obj is a variable, array, function or subroutine whose address is wanted. iaddr is an integer with the address of "obj". The address is in the same format as stored by an LARn instruction.

Description:

LOC is used to obtain the address of something. The value returned is not really useful within Fortran, but may be needed for GMAP subroutines, or very special debugging.

Upvotes: 4

Views: 672

Answers (2)

robince
robince

Reputation: 10967

Gfortran loc seems to work a bit differently with arrays to that of some other compilers. If you are using it to eg check for array copies or such then it can be better to do loc of the first element loc(obj(1,1)) or similar. This is equivalent to what loc does I think with intel, but in gfortran it gives instead some other address (so two arrays which share exactly the same memory layout have different loc results).

Upvotes: 0

Jonathan Dursi
Jonathan Dursi

Reputation: 50937

Well, no, the fact that it compiles means that loc is known by the compiler; the fact that gdb doesn't know about it just means it's just not known by the debugger (which probably doesn't know the matmult intrinsic, either).

loc is a widely-available non-standard extension. I hate those. If you want something standard that should work everywhere, c_loc, which is part of the C<->Fortran interoperability standard in Fortran2003, is something you could use. It returns a pointer that can be passed to C routines.

How is the value from the loc call being used?

Upvotes: 5

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