OPTIONS Directive

Syntax

cDEC$ OPTIONS option[option]

...

cDEC$ END OPTIONS

c

Is one of the following: C (or c), !, or *. (See Syntax Rules for Compiler Directives.)

option

Is one (or both) of the following: /WARN=[NO]ALIGNMENT Controls whether warnings are issued by the compiler for data that is not naturally aligned. By default, you receive compiler messages when misaligned data is encountered (/WARN=ALIGNMENT). /[NO]ALIGN[= p] Controls alignment of fields in record structures and data items in common blocks. The fields and data items can be naturally aligned (for performance reasons) or they can be packed together on arbitrary byte boundaries. p Is a specifier with one of the following forms: [class=]rule (class= rule,...) ALL NONE class Is one of the following keywords: COMMONS: For common blocks RECORDS: For records STRUCTURES: A synonym for RECORDS rule Is one of the following keywords: PACKED Packs fields in records or data items in common blocks on arbitrary byte boundaries. NATURAL Naturally aligns fields in records and data items in common blocks on up to 64-bit boundaries (inconsistent with the Fortran 95/90 standard). This keyword causes the compiler to naturally align all data in a common block, including INTEGER(KIND=8), REAL(KIND=8), and all COMPLEX data. STANDARD Naturally aligns data items in common blocks on up to 32-bit boundaries (consistent with the Fortran 95/90 standard). This keyword only applies to common blocks; so, you can specify /ALIGN=COMMONS=STANDARD, but you cannot specify /ALIGN=STANDARD. ALL Is the same as specifying OPTIONS /ALIGN, OPTIONS /ALIGN=NATURAL, and OPTIONS /ALIGN=(RECORDS=NATURAL,COMMONS=NATURAL). NONE Is the same as specifying OPTIONS /NOALIGN, OPTIONS /ALIGN=PACKED, and OPTIONS /ALIGN=(RECORDS=PACKED,COMMONS=PACKED).

The OPTIONS (and accompanying END OPTIONS) directives must come after OPTIONS, SUBROUTINE, FUNCTION, and BLOCK DATA statements (if any) in the program unit, and before the executable part of the program unit.

The OPTIONS directive supersedes compiler option align.

For performance reasons, Intel Fortran aligns local data items on natural boundaries. However, EQUIVALENCE, COMMON, RECORD, and STRUCTURE data declaration statements can force misaligned data. If /WARN=NOALIGNMENT is specified, warnings will not be issued if misaligned data is encountered.

Note

Misaligned data significantly increases the time it takes to execute a program. As the number of misaligned fields encountered increases, so does the time needed to complete program execution. Specifying /ALIGN (or compiler option align) minimizes misaligned data.

If you want aligned data in common blocks, do one of the following:

• Specify OPTIONS /ALIGN=COMMONS=STANDARD for data items up to 32 bits in length.

• Specify OPTIONS /ALIGN=COMMONS=NATURAL for data items up to 64 bits in length.

• Place source data declarations within the common block in descending size order, so that each data item is naturally aligned.

If you want packed, unaligned data in a record structure, do one of the following:

• Specify OPTIONS /ALIGN=RECORDS=PACKED.

• Place source data declarations in the record structure so that the data is naturally aligned.

Example

! directives can be nested up to 100 levels

CDEC$ OPTIONS /ALIGN=PACKED ! Start of Group A

declarations

CDEC$ OPTIONS /ALIGN=RECO=NATU ! Start of nested Group B

more declarations

CDEC$ END OPTIONS ! End of Group B

still more declarations

CDEC$ END OPTIONS ! End of Group A

The OPTIONS specification for Group B only applies to RECORDS; common blocks within Group B will be PACKED. This is because COMMONS retains the previous setting (in this case, from the Group A specification).