FORTRAN code

Programs written in FORTRAN  must conform to the ANSI FORTRAN-77 specifications defined by ISO Std. 1539-1980(E) [6]. Five extensions may be used to improve readability and structure of the code. They can be removed by the MIDAS utility esoext. The five extensions are:

• IMPLICIT NONE statements must be specified in each file in order to ensure all variables are declared explicitly.
• INCLUDE statements may be used to include files with common definitions, etc.
• !-comments may be used to add comments at the end of a statement line. All characters including and after an !-mark on a line will be regarded as comments. The usage of such comments is strongly encourage because it significantly improves the documentation.
• DO/ENDDO statements may be used for convenience instead of the standard FORTRAN-77 DO/CONTINUE statements.
• Long identifiers with up to 16 character including underscores may be used. The first five and the last character (excluding underscores) must yield a unique identifier.

The usage of these extensions is not mandatory; however, the three first extensions are recommended in order to ensure that all variables are declared, definitions are common in all modules and that the code is fully documented with in-line comments.

The FORTRAN code must obey the following rules:

• All variables must be declared explicitly with type. This may be ensured by using the IMPLICIT NONE statement or using a compiler option which checks this.
• Indentation of at least two columns must be made for each level of IF/ELSE/ENDIF and DO/END/CONTINUE statements. For long DO-loops, additional comments at their start and end are strongly encouraged. Further, statement labels must clearly indicate the loop structure and hierarchy.
• Statement labels should be given in increasing order and reflect the logical structure of the program. The number range 80000-81000 should be avoided because it is used by the MIDAS preprocessor.
• When using DO/CONTINUE statements, it is recommended to terminate the statement label after the DO with a ','(ref. ANSI FORTRAN-77) to avoid misinterpretation even through typing errors.
• Include files should not contain executable code statements.
• Each module must contain a comment header block which defines name, purpose, author, version etc. (see Section ).
• Subroutines and functions may share the source file with a main program only if they are not used in any other module.
• Internal READ statements using free or list-directed format are not allowed (e.g. READ(LINE,*)). The general usage of internal READ is deprecated due to usage of explicit editing formats.

To make the code easier to understand, the usage of frequent comments, meaningful variable names and spaces between elements are recommended whereas GOTO statements are strongly discouraged.

A number of FORTRAN-77 statements and features have been defined obsolete by FORTRAN-90. Although they are still valid in FORTRAN-90, they may be recommended for deletion in new revisions. The usage of features on the FORTRAN-90 list of obsolescent features is deprecated for MIDAS application written in FORTRAN in order to ensure the longest possible life time of the code. The current list of obsolescent features in FORTRAN-90 is:

• arithmetic IF;
• branching to an ENDIF statement from outside its block;
• real and double precision DO variables and control expressions;
• shared DO termination, and DO termination on a statement other than on a CONTINUE and an ENDDO statement;
• ASSIGN and the assigned GOTO;
• alternate RETURN;
• PAUSE statement; and
• assigned FORMAT specifiers.

It should be noted that all 5 ESO extensions to FORTRAN-77 are included in FORTRAN-90.