6.5 Intrinsic and Library Procedures

Fortran 90 defines over 100 built-in or intrinsic procedures, some inherited from Fortran 77, some new (see the Fortran Language Reference Manual). In addition, HPF introduces new intrinsic procedures. HPF also defines a library module HPF_LIBRARY that adds further to the power of the language.

6.5.1 Intrinsic Procedures

HPF adds the following to the standard Fortran 90 intrinsic procedures:

• System inquiry functions NUMBER_OF_PROCESSORS and PROCESSORS_SHAPE
• Enhancements to the Fortran 90 intrinsic functions MAXLOC and MINLOC
• A new elemental intrinsic function ILEN to compute the number of bits needed to store an integer value

All Intrinsic procedures are PURE, except for RAN and SECNDS.

The intrinsic procedures that reference the system clock require special consideration in parallel HPF programs, because more than one system clock may be referenced if multiple hosts are involved in the execution. Only SECNDS synchronizes the processors to ensure consistency (at some cost in performance). The other time intrinsics do not guarantee consistency of clocks of different systems.

For a complete list of the intrinsic procedures provided with Digital Fortran 90, see the Fortran Language Reference Manual.

6.5.2 Library Procedures

Digital Fortran 90 anticipates many operations that are valuable for parallel algorithm design. HPF adds a standard library of functions which includes:

• Mapping inquiry subroutines to determine the actual data mapping of arrays at run time
• Bit manipulation functions LEADZ, POPCNT, and POPPAR
• New array reduction functions IALL, IANY, IPARITY, and PARITY
• Array combining scatter functions, one for each reduction function
• Array prefix and suffix functions, one each for each reduction function
• Two array sorting functions

For a complete list of the library procedures provided with Digital Fortran 90, see the Fortran Language Reference Manual.