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HPF is an extension of Fortran 90. The array calculation and dynamic storage allocation features of Fortran 90 make it a natural base for HPF. The new HPF language features fall into four categories with respect to Fortran 90:
The new directives are structured comments that suggest implementation strategies or assert facts about a program to the compiler. They may affect the efficiency of the computation performed, but do not change the value computed by the program. The form of the HPF directives has been chosen so that a future Fortran standard may choose to include these features as full statements in the language by deleting the initial comment header.
A few new language features, including the FORALL statement and a few intrinsic functions, are also defined. They were made first-class language constructs rather than comments because they can affect the interpretation of a program, for example by returning a value used in an expression. These are proposed as direct extensions to the Fortran 90 syntax and interpretation.
The HPF library of computational functions defines a standard interface to routines that have proven valuable for high performance computing including additional reduction functions, combining scatter functions, prefix and suffix functions, and sorting functions.
Full support of Fortran sequence and storage association is not compatible with the data distribution features of HPF. Some restrictions on the use of sequence and storage association are defined. These restrictions may in turn require insertion of HPF directives into standard Fortran 90 programs in order to preserve correct semantics.