Development [LWN.net]

The status of the GNU Fortran project

November 30, 2005

This article was contributed by Kenneth Geisshirt

Fortran is one of the oldest programming languages. With its roots back to the 1950s at the scientific community, the language has evolved heavily over half a century. The evolution of Fortran reflects the changes in the computing industry. In the 1950s computers were programmed in machine language, and translating mathematical formulas into machine language was indeed difficult. The system for FORmula TRANslation was developed.

Today, Fortran is primarily used by scientists and engineers. There is a wide variety of free and non-free scientific software written in Fortran. A lot of the free Fortran software comes from University professors. Just as important, a number of small software companies develop and sell software for limited or specialized market segments. Examples of such software is the quantum chemistry package Gaussian 03 and Adina, the Finite Element System for Structures, Heat Transfer, and CFD.

In the UNIXes of the 1980s, the most common variant of Fortran was Fortran-77. At AT&T Bell Laboratories the free translator f2c was developed. Translation from Fortran-77 to ISO C required a large runtime library in order to compile the resulting C code. Later, a front-end for GCC, the GNU C compiler (now GNU Compiler Collection) was developed using the same runtime library. The GNU Fortran 77 (g77) team, lead by James Craig Burley, stopped development after it was determined that g77 was sufficient to meet the requirements of its users. The front-end is still included in the GNU Compiler Collection prior to version 4. It is available at the g77 Legacy Site.

In year 2000, a new Fortran project entered the GNU scene - GNU Fortran 95 (G95). The goal of the G95 project is to implement the Fortran variant or standard from 1995 (ISO/IEC 1539:1997). Currently, no bugs are known!

With the release of version 4 of GCC in April, 2005, Fortran 95 was included as one of the new languages. In GCC 4, the Fortran 95 language is fully implemented. A valid Fortran 95 program should compile, while an invalid Fortran 95 will be rejected. GFortran uses the Tree-SSA middle of GCC, and therefore the same back-end (or code generators) and by that, GFortran is supported on a large number of architectures. But there exists a number of issues with the front-end including a need for better error messages.

Fortran has a large number of intrinsic functions. These functions are defined in the specification of the language, they are not implemented as a library subroutine as you might see in languages like C and C++. Examples of Intrinsic functions include the performing of averages of elements in an array and calculating dot products between two vectors/arrays. The set of I/O intrinsic functions is still limited. Most programs do not use the advanced I/O intrinsics, and these programs will work perfectly. Software that uses advanced I/O intrinsics might prove to be challenging to implement.

As of this writing, a large number of free software packages can be compiled using GFortran. Of course, most of the available packages are related to the scientific and engineering fields.

One of the nice things about GFortran programs is that you can suspend them during runtime. When the program receives a QUIT signal, a core dump will be generated. Later, you can restart the program from this core dump. This is a useful feature when your software reaches the CPU limit, this tends to be something that is tightly enforced in supercomputing centers around the world.

Even though the documentation is extensive, it might not be up to date with the latest releases of GFortran. Most of the development in the GFortran project is focused on implementing new intrinsics and optimizing the implementation of the existing intrinsics. The web pages related to GFortran are not well maintained. If you're looking for a non-technical role in a free software project, here's your chance to make a contribution.

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