3.1 Adherence to standards and use of extensions

Very early in the development it became apparent that strict adherence to the Fortran 77 standard was needlessly restrictive, since:

• every platform of interest supports a useful common set of extensions, and
• Fortran 90, which standardized many of the useful extensions, had become the new official Fortran standard, and compilers were starting to appear.

I therefore made the decision to use any extensions necessary as long as they were supported on all platforms of interest, and they did not conflict with Fortran 90 standards.

Below is a list of extensions to Fortran 77 used by JTPACK77:

• Extended character set. Examples:
  • Lowercase characters.
  • ``&'' as continuation symbol.
  • ``_'' in routine and variable names.
  • Quotes (") in comments and output strings.

• Routine and variable names longer than six characters.
• ``Do/end do'' rather than ``do/continue''.
• Dynamic allocation of arrays (often Cray pointers).
• Comments embedded in code (via ``!'').
• System calls (e.g. ETIME, SYSTEM).
• Array elements as dimension bounds.

In the last case, I actually break my own rule of only using extensions available on all platforms, since Sun removed (undocumented) support for this extension as of version 3.0 (this brings to light one of the disadvantages of using extensions). In fact, due to some of the internals of JTPACK77, this particular change required a fairly ugly hack to work around. However, since it is supported in Fortran 90, I decided to maintain use of it on those platforms that support it, since it results in much cleaner code.