User's Guide

Outline of the Porting Process

The process for porting a typical program looks like this:

1. Identify any nonportable language extensions or subroutines that you used in the original program. Check to see which of these XL Fortran supports:

   • You can find language extensions in the XL Fortran for AIX Language Reference, highlighted in blue.

   • Some extensions require you to specify an XL Fortran compiler option; you can find these options listed in Figure 10.

2. For any nonportable features that XL Fortran does not support, modify the source files to remove or work around them.

3. Do the same for any implementation-dependent features. For example, if your program relies on the representation of floating-point values or uses system-specific file names, you may need to change it.

4. Compile the program with XL Fortran. If any compilation problems occur, fix them and recompile and fix any additional errors until the program compiles successfully.

5. Run the XLF-compiled program and compare the output with the output from the other system. If the results are substantially different, there are probably still some implementation-specific features that need to be changed. If the results are only marginally different (for example, if XL Fortran produces a different number of digits of precision or a number differs in the last decimal place), decide whether the difference is significant enough to investigate further. You may be able to fix these differences, but finding the correct solution may be time-consuming.

Before porting programs to XL Fortran, read the tips in the following sections so that you know in advance what compatibility features XL Fortran offers. An easy way to choose options that reflect your goals is to run the xxlf command. This presents a point-and-click interface to different categories of compiler options.

Figure 40. Portability Window of the xxlf Application