gfortran on MacOS X

gfortran Building Procedure (gcc-4.1 based)

gcc-4.0 that comes with Apple's standard DevTools does not include "gfortran", the GNU fortran 95 compiler. Although its source tree does include one, building gfortran from Apple's source tree requires some patching to satisfy undefined references caused by Apple's modifications that broke Language independence. Moreover, the gfortran source files are not up-to-date and require a lot of patching to be usable: I had been using the patched versions for sometime but recently switched to the version from the SVN source tree for gcc-4.1. In order to make gcc-4.1 coexist with Apple's gcc-4.0, I decided to configure gcc-4.1 to be installed under /usr/local. To build gcc-4.1, first get the source files from the official SVN site for gcc, cd into the source directory and do the following:

$ ./configure --prefix=/usr/local --disable-checking --enable-languages=c,c++,f95
$ make
$ mkdir tmp
$ make install DESTDIR=`pwd`/tmp
$ cd tmp
$ su
# chown -R root:wheel usr
# tar -zcvf gcc-4.1.0-bin.tar.gz usr
# exit

This gives you a tarball of gcc-4.1 compiler suite including gcc, g++, and gfortran, which can be expanded at the root directory to install under /usr/local.

How to Install a Precompiled Binary Package

A binary package is available as an RPM which can be installed using APT/RPM as

$ su
# apt-get update
# apt-get install gcc
# apt-get clean
# exit

Since the package is installed under /usr/local, you can use the gcc-4.1 as your default compiler suite by putting /usr/local/bin in front of /usr/bin in your PATH environmental variable.
 

REMARKS

• As a general rule, you should make sure that optimization does not change your results.
• Avoid too many else if's in the same level. You sometimes need to nest them, if the compiler abends.
• A blanket "SAVE" and an idividual "SAVE symbol" do not coexit.
• gfortran forbids jumping into a different "IF" block.
• gfortran does not initialize a "BLOCK DATA" even if you declare it "EXTERNAL". In order to force it, say "blkdat", initialized, I needed a trick like
  
      external blkdat
      call dummysub(blkdat)
  
  with
      subroutine dummysub(a)
      return
      end
  
  
• gfortran returns IOSTAT=3 when the EOF is reached for an random access file, which behavior is different from that of g77.
• gcc, g++, and gfortran now use system's math library (libm.dylib), whenever possible, which sometimes causes a problem, since some functions in libm behave differently from those used to be supplied by gcc-associated libraries (a typical example is "csqrt": see cernlib page).
• Add
  
      -ftree-vectorize
  
  if you want automatic vectorization to use velocity engine.
• Here is a sample FCFLAGS I usually use to compile my legacy fortran programs:
  
      FCFLAGS = -fno-automatic -fno-second-underscore