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copied!<p>You kind of have to get a "feel" for what programmers had to do back in the day. The vast majority of the code I work with is older than I am and ran on machines that were "new" when my parents were in high school.</p> <p>Common FORTRAN-isms I deal with, that hurt readability are:</p> <ul> <li>Common blocks</li> <li>Implicit variables</li> <li>Two or three DO loops with shared CONTINUE statements</li> <li>GOTO's in place of DO loops</li> <li>Arithmetic IF statements</li> <li>Computed GOTO's</li> <li>Equivalence REAL/INTEGER/other in some common block</li> </ul> <p>Strategies for solving these involve:</p> <ol> <li>Get <a href="http://www.polyhedron.com/spag0html" rel="noreferrer">Spag / plusFORT</a>, worth the money, it solves a lot of them automatically and Bug Free(tm)</li> <li>Move to Fortran 90 if at all possible, if not move to free-format Fortran 77</li> <li>Add IMPLICIT NONE to each subroutine and then fix every compile error, time consuming but ultimately necessary, some programs can do this for you automatically (or you can script it)</li> <li>Moving all COMMON blocks to MODULEs, low hanging fruit, worth it</li> <li>Convert arithmetic IF statements to IF..ELSEIF..ELSE blocks</li> <li>Convert computed GOTOs to SELECT CASE blocks</li> <li><p>Convert all DO loops to the newer F90 syntax</p> <pre><code>myloop: do ii = 1, nloops ! do something enddo myloop </code></pre></li> <li><p>Convert equivalenced common block members to either ALLOCATABLE memory allocated in a module, or to their true character routines if it is Hollerith being stored in a REAL</p></li> </ol> <p>If you had more specific questions as to how to accomplish some readability tasks, I can give advice. I have a code base of a few hundred thousand lines of Fortran which was written over the span of 40 years that I am in some way responsible for, so I've probably run across any "problems" you may have found.</p>

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