| Previous | Contents | Index |
The PACK directive specifies the memory starting addresses of derived-type or record structure items. This directive takes the following form: 1
|
c
Is one of the following: C (or c), !, or * (see Section 14.1).
Items of derived types and record structures are aligned in memory on the smaller of two sizes: the size of the type of the item, or the current alignment setting. The current alignment setting can be 1, 2, 4, or 8 bytes. The default initial setting is 8 bytes (unless a compiler option specifies otherwise). By reducing the alignment setting, you can pack variables closer together in memory.
The PACK directive lets you control the packing of derived-type or record structure items inside your program by overriding the current memory alignment setting.
For example, if CDEC$ PACK:1 is specified, all variables begin at the next available byte, whether odd or even. Although this slightly increases access time, no memory space is wasted. If CDEC$ PACK:4 is specified, INTEGER(1), LOGICAL(1), and all character variables begin at the next available byte, whether odd or even. INTEGER(2) and LOGICAL(2) begin on the next even byte; all other variables begin on 4-byte boundaries.
If the PACK directive is specified without a number, packing reverts to the compiler option setting (if any), or the default setting of 8.
The directive can appear anywhere in a program before the derived-type definition or record structure definition. It cannot appear inside a derived-type or record structure definition.
Consider the following:
! Use 4-byte packing for this derived type ! Note PACK is used outside of the derived-type definition !DEC$ PACK:4 TYPE pair INTEGER a, b END TYPE ! revert to default or compiler option !DEC$ PACK: |
1 The following form is also allowed: !MS$PACK:[{1|2|4}]. |
The PSECT directive modifies several characteristics of a common block.
It takes the following form:
Global or local scope is significant for an image that has more than
one cluster. Program sections with the same name that are from
different modules in different clusters are placed in separate clusters
if local scope is in effect. They are placed in the same cluster if
global scope is in effect.
If one program unit changes one or more characteristics of a common
block, all other units that reference that common block must also
change those characteristics in the same way.
Default characteristics apply if you do not modify them with a PSECT
directive. Table 14-1 lists the default characteristics of common
blocks and how they can be modified by PSECT.
14.16 PSECT Directive
c
Is one of the following: C (or c), !, or * (see Section 14.1).
common-name
Is the name of the common block. The slashes (/) are required.
a
Is one of the following keywords:
Specifies
alignment for the common block.
The val is a constant
ranging from 0 through 16. The specified number is interpreted as a
power of 2. The value of the expression is the alignment in bytes.
The keyword is one of the following:
Keyword
Equivalent to val
BYTE
0
WORD
1
LONG
2
QUAD
3
OCTA
4
PAGE
1
Alpha: 16
I64: 13
1Range for Alpha is 0 to 16; for I64, 0 to 13.
Specifies global scope.
Specifies local scope. This keyword is opposite to GBL and
cannot appear with it.
Controls whether the compiler pads the size
of common blocks to ensure compatibility when the common block program
section (psect) is shared by code created by other HP compilers.
When a program section generated by a Fortran common block is
overlaid with a program section consisting of a C structure, linker
error messages can occur. This is because the sizes of the program
sections are inconsistent; the C structure is padded, but the Fortran
common block is not.
Specifying MULTILANGUAGE ensures that
HP Fortran follows a consistent program section size allocation
scheme that works with HP C program sections shared across multiple
images. Program sections shared in a single image do not have a
problem.
You can use a compiler option to specify MULTILANGUAGE for
all common blocks in a module.
Determines whether the contents of a common block can
be shared by more than one process.
Determines whether the contents of a common block can
be modified during program execution.
Default Characteristics
PSECT Modification
Relocatable
None
Overlaid
None
Global Scope
Global or local scope
Not executable
None
Not multilanguage
Multilanguage or not multilanguage
Writable
Writable or not writable
Readable
None
No protection
None
Octaword alignment
1 (4)
0 through 16
2
Not shareable
Shareable or not shareable
Position dependent
None
1An address that is an integral multiple of 16.
2Or keywords BYTE through PAGE.
The REAL directive specifies the default real kind. This directive takes the following form: 1
|
c
Is one of the following: C (or c), !, or * (see Section 14.1).
The REAL directive specifies a size of 4 (KIND=4), 8 (KIND=8), or 16 (KIND=16) bytes for default real numbers.
When the REAL directive is effect, all default real variables are of the kind specified in the directive. Only numbers specified or implied as REAL without KIND are affected.
The REAL directive can only appear at the top of a program unit. A program unit is a main program, an external subroutine or function, a module or a block data program unit. The directive cannot appear between program units, or at the beginning of internal subprograms. It does not affect modules invoked with the USE statement in the program unit that contains it.
Consider the following:
REAL r ! a 4-byte REAL
WRITE(*,*) KIND(r)
CALL REAL8( )
WRITE(*,*) KIND(r) ! still a 4-byte REAL
! not affected by setting in subroutine
END
SUBROUTINE REAL8( )
!DEC$ REAL:8
REAL s ! an 8-byte REAL
WRITE(*,*) KIND(s)
END SUBROUTINE
|
1 The following form is also allowed: !MS$REAL:{4|8}. |
The STRICT directive disables language features not found in the
language standard specified on the command line (Fortran 95 or Fortran
90). The NOSTRICT directive (the default) enables these language
features.
These directives take the following forms: 1
If STRICT is specified and no language standard is specified on the
command line, the default is to disable features not found in Fortran
90.
The STRICT and NOSTRICT directives can appear only appear at the top of
a program unit. A program unit is a main program, an external
subroutine or function, a module or a block data program unit. The
directives cannot appear between program units, or at the beginning of
internal subprograms. They do not affect any modules invoked with the
USE statement in the program unit that contains them.
Consider the following:
14.18 STRICT and NOSTRICT Directives
c
Is one of the following: C (or c), !, or * (see Section 14.1).
! NOSTRICT by default
TYPE stuff
INTEGER(4) k
INTEGER(4) m
CHARACTER(4) name
END TYPE stuff
TYPE (stuff) examp
DOUBLE COMPLEX cd ! non-standard data type, no error
cd =(3.0D0, 4.0D0)
examp.k = 4 ! non-standard component designation,
! no error
END
SUBROUTINE STRICTDEMO( )
!DEC$ STRICT
TYPE stuff
INTEGER(4) k
INTEGER(4) m
CHARACTER(4) name
END TYPE stuff
TYPE (stuff) samp
DOUBLE COMPLEX cd ! ERROR
cd =(3.0D0, 4.0D0)
samp.k = 4 ! ERROR
END SUBROUTINE
On syntax rules for all general directives, see Section 14.1.
1 The following forms are also allowed: !MS$STRICT and !MS$NOSTRICT. |
The TITLE directive specifies a string for the title field of a listing
header. Similarly, SUBTITLE specifies a string for the subtitle field
of a listing header.
These directives take the following forms: 1
To enable TITLE and SUBTITLE directives, you must specify the compiler
option that produces a source listing file.
When TITLE or SUBTITLE appear on a page of a listing file, the
specified string appears in the listing header of the following page.
If two or more of either directive appear on a page, the last directive
is the one in effect for the following page.
If neither directive specifies a string, no change occurs in the
listing file header.
14.19 TITLE and SUBTITLE Directives
c
Is one of the following: C (or c), !, or * (see Section 14.1).
string
Is a character constant containing up to 31 printable characters.
1 The following forms are also allowed: !MS$TITLE:string and !MS$SUBTITLE:string. |
The UNROLL directive tells the compiler's optimizer how many times to
unroll a DO loop. This directive can only be applied to iterative DO
loops.
The UNROLL directive takes the following form:
The UNROLL directive must precede the DO statement for each DO loop it
affects. No source code lines, other than the following, can be placed
between the UNROLL directive statement and the DO statement:
If n is specified, the optimizer unrolls the loop n
times. If n is omitted, or if it is outside the allowed range,
the optimizer picks the number of times to unroll the loop.
The UNROLL directive overrides any setting of loop unrolling from the
command line.
14.20 UNROLL Directive
c
Is one of the following: C (or c), !, or * (see Section 14.1).
n
Is an integer constant. The range of n is 0 through 255.
On syntax rules for all general directives, see Section 14.1.
This chapter describes:
Program entities are identified by names, labels, input/output unit numbers, operator symbols, or assignment symbols. For example, a variable, a derived type, or a subroutine is identified by its name.
Scope refers to the area in which a name is recognized. A scoping unit is the program or part of a program in which a name is defined and known. It can be any of the following:
The region of the program in which a name is known and accessible is referred to as the scope of that name. These different scopes allow the same name to be used for different things in different regions of the program.
Association is the language concept that allows
different names to refer to the same entity in a particular region of a
program.
15.2 Scope
Program entities have the following kinds of scope (as shown in Table 15-1):
| Entity | Scope | |
|---|---|---|
| Program units | Global | |
| Common blocks 1 | Global | |
| External procedures | Global | |
| Intrinsic procedures | Global 2 | |
| Module procedures | Local | Class I |
| Internal procedures | Local | Class I |
| Dummy procedures | Local | Class I |
| Statement functions | Local | Class I |
| Derived types | Local | Class I |
| Components of derived types | Local | Class II |
| Named constants | Local | Class I |
| Named constructs | Local | Class I |
| Namelist group names | Local | Class I |
| Generic identifiers | Local | Class I |
| Argument keywords in procedures | Local | Class III |
| Variables that can be referenced throughout a subprogram | Local | Class I |
| Variables that are dummy arguments in statement functions | Statement | |
| DO variables in an implied-do list 3 of a DATA or FORALL statement, or an array constructor | Statement | |
| Intrinsic operators | Global | |
| Defined operators | Local | |
| Statement labels | Local | |
| External I/O unit numbers | Global | |
| Intrinsic assignment | Global 4 | |
| Defined assignment | Local |
Scoping units can contain other scoping units. For example, the following shows six scoping units:
MODULE MOD_1 ! Scoping unit 1
... ! Scoping unit 1
CONTAINS ! Scoping unit 1
FUNCTION FIRST ! Scoping unit 2
TYPE NAME ! Scoping unit 3
... ! Scoping unit 3
END TYPE NAME ! Scoping unit 3
... ! Scoping unit 2
CONTAINS ! Scoping unit 2
SUBROUTINE SUB_B ! Scoping unit 4
TYPE PROCESS ! Scoping unit 5
... ! Scoping unit 5
END TYPE PROCESS ! Scoping unit 5
INTERFACE ! Scoping unit 5
SUBROUTINE SUB_A ! Scoping unit 6
... ! Scoping unit 6
END SUBROUTINE SUB_A ! Scoping unit 6
END INTERFACE ! Scoping unit 5
END SUBROUTINE SUB_B ! Scoping unit 4
END FUNCTION FIRST ! Scoping unit 2
END MODULE ! Scoping unit 1
|
| Previous | Next | Contents | Index |