Fortran/GNU

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• • Compiling FLEXPART with the GNU Fortran compiler gfortran**

The advantages of the gfortran compiler as it stands now (gfortran with gcc 4.3.2) is that it can compile for 64Bit which means it can address more than 2GB of memory.

There are two additional makefiles for the ecmwf input routines when you check out FLEXPART from the svn server:

• make.ecmwf_gfortran*

• make.ecmwf_gfortran_64*

The compiler settings for 32Bit (in *make.ecmwf_gfortran*) are:

 FC       = gfortran
 INCPATH  = /nilu/home/flexpart/lib/grib_api/include
 LIBPATH1 = /nilu/home/flexpart/lib/grib_api/lib
 LIBPATH2 = /nilu/home/flexpart/lib/jasper/lib
 FFLAGS   =   -O3 -m32 -fconvert=little-endian -I$(INCPATH)
 LDFLAGS  = $(FFLAGS) -L$(LIBPATH2) -L$(LIBPATH1) -lgrib_api_f90 -lgrib_api -lm -ljasper

The compiler settings for 64Bit (in *make.ecmwf_gfortran_64*) are:

 FC       = gfortran
 INCPATH  = /nilu/home/flexpart/lib64/grib_api/include
 LIBPATH1 = /nilu/home/flexpart/lib64/grib_api/lib
 LIBPATH2 = /nilu/home/flexpart/lib64/jasper/lib
 FFLAGS   =   -O3 -m64 -mcmodel=large -fconvert=little-endian -frecord-marker=4 -I$(INCPATH)
 LDFLAGS  = $(FFLAGS) -L$(LIBPATH2) -L$(LIBPATH1) -lgrib_api_f90 -lgrib_api -lm -ljasper

Explanation of the options for the unformatted output from the `GCC 4.3.2 documentation <http://gcc.gnu.org/onlinedocs/gcc-4.3.2/gcc/i386-and-x86_002d64-Options.html#i386-and-x86_002d64-Options>`_

 -fconvert=conversion
 Specify the representation of data for unformatted files. Valid values for conversion are: `native', the default; `swap', swap between big- and
 little-endian; `big-endian', use   big-endian representation for unformatted files; `little-endian', use little-endian representation for 
 unformatted files. This option has an effect only when used in the main program. The CONVERT specifier and the GFORTRAN_CONVERT_UNIT environment 
 variable override the default specified by -fconvert.

 -frecord-marker=length
 Specify the length of record markers for unformatted files. Valid values for length are 4 and 8. Default is whatever off_t is specified to be on 
 that particular system. Note that specifying length as 4 limits the record length of unformatted files to 2 GB. This option does not extend the 
 maximum possible record length on systems where off_t is a four_byte quantity.

Explanation of the options for the memory model

 -mcmodel=small
 Generate code for the small code model: the program and its symbols must be linked in the lower 2 GB of the address space. Pointers are 64 bits. 
 Programs can be statically or dynamically linked. This is the default code model. 
 
 -mcmodel=medium
 Generate code for the medium model: The program is linked in the lower 2 GB of the address space but symbols can be located anywhere in the 
 address space. Programs can be   statically or dynamically linked, but building of shared libraries are not supported with the medium model. 
 
 -mcmodel=large
 Generate code for the large model: This model makes no assumptions about addresses and sizes of sections.
 

• • Note:** on the 64-Bit machines which are not yet updated to the new Fedora release, gfortran is at version 4.1.2, which not yet supports the option *-mcmodel=large*. Instead use the option *-mcmodel=medium* when compiling on billy, sjanten and jegern until they are updated.

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