LOC(3I) Last changed: 2-5-98
NAMELOC - Obtains the word address of a variable
SYNOPSISLOC ([I=]i)
IMPLEMENTATION
UNICOS, UNICOS/mk, and IRIX systems
STANDARDS
CF90 and MIPSpro 7 Fortran 90 compiler extension to Fortran 90
DESCRIPTIONLOC returns the address of a variable, constant, or array. On UNICOS
systems, the address returned is a word address. On UNICOS/mk and
IRIX systems, the address returned is a byte address. It accepts the
following arguments:
i The address to be returned. Specify a variable or constant of
Boolean, integer, real, logical, complex, Cray pointer, or
character type.
LOC can be used to define a Cray pointer. Just like a variable in
common storage, a Cray pointee, Cray pointer, or the i argument to LOC
is stored in memory before a call to an external procedure and is read
out of memory at its next reference. The variable is also stored
before a RETURN or END statement of a subprogram.
The name of this intrinsic cannot be passed as an argument.
WARNINGSLOC is often used to compute the difference of two addresses as an
offset. The offset is then used to access one of the arrays by
overindexing the other array. UNICOS/mk systems, unlike UNICOS
systems, have several address spaces (called memory segments), and
memory references with offsets outside of the segment are not allowed.
If the arrays are in different memory segments, the corresponding
offset generates memory references outside of the segment. These
references cause run-time Translation Not Valid errors.
RETURN VALUES
The value returned is of type Cray pointer.
EXAMPLES
Example 1: Consider the following code:
SUBROUTINE SUB(N)
COMMON POOL(100000)
INTEGER BLK(128), WORD64
REAL A(1000), B(N), C(100000-N-1000)
POINTER(PBLK,BLK),(IA,A),(IB,B),(IC,C),(ADDRESS,WORD64)
DATA ADDRESS /64/
PBLK = 0
IA = LOC(POOL)
IB = IA + 1000
IC = IB + N
In effect, WORD64 in this example refers to the contents of absolute
address 64; BLK is an array occupying the first 128 words of memory; A
is an array of length 1000 located in blank common; B follows A and is
of length N; C follows B. A, B, and C are associated with POOL.
Similarly, WORD64 is the same as BLK(65), because BLK(1) is at address
0.
Example 2: Consider the following code:
POINTER (P,B),(P,C)
REAL X,B,C
P = LOC(X)
B = 1.0
C = 2.0
PRINT *,B
Because B and C have the same Cray pointer, the assignment of 2.0 to C
gives the same value to B; therefore, B will print as 2.0 even though
it was assigned 1.0.
SEE ALSO
Intrinsic Procedures Reference Manual, publication SR-2138, for the
printed version of this man page.
