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Facilidade de uso
Improving Performance
Indexing Guidelines
STACK and
STACK and STORE statements do not improve the efficiency of access to data items.
STORE Statements
These statements are provided primarily for moving operands to and from the register
stack when working with the CODE statement.
Indexing Guidelines
The compiler saves index values in index registers so you can refer to them in later
statements. For instance, for the following operation, the compiler saves the value of I
in an index register:
x[i] := 5;
You can then use I in a reference such as Y[I].
Multiple references to the same index value (using the same data type) promote
efficiency.
For indexed items in structures, the compiler optimizes references only to adjacent
items within the same substructure.
An index on a 16-bit variable is always a signed INT expression. For a STRING
variable, an index can access ranges from 32K bytes below to 32K bytes above the
zeroth structure occurrence. For any variable except a STRING variable, an index can
access ranges from 32K words below to 32K words above the zeroth structure
occurrence.
Indexing indirect references is no less efficient than not indexing indirect references,
because the hardware requires no extra time to add indexes to address values.
For an INT or STRING extended pointer located below G[63] or L[63] (decimal), a 16-
bit index is more efficient than a 32-bit index. A 16-bit index results in a shorter
instruction sequence using the LWXX, SWXX, LBXX, and SBXX instructions. (These
instructions are described in the System Description Manual for your system.)
For all other extended pointers, a 16-bit index is slightly more efficient than a 32-bit
index. If, however, the offset of a structure item declared in an extended indirect
structure is outside the signed INT range (–32,768 through 32,767), you must use a 32-
bit index.
In a program written for a D-series system, you can use the INT32INDEX directive
when you index an extended indirect structure item. INT32INDEX suppresses the
[NO]INHIBITXX directive and generates a 32-bit index from a 16-bit index. If you use
INT32INDEX, you need not calculate the offset of an extended structure item to
determine whether to use a 16-bit or a 32--bit index. INT32INDEX always generates
correct offsets but is slightly less efficient than using a 32-bit index. For more
information, see “Indexing Structures” in Section 8, “Using Structures.”
Using a USE register for the 16-bit index of an extended pointer does not provide
further efficiency. The compiler must still load the index value from the USE register
into register A for use with the LWXX, SWXX, LBXX, and SBXX instructions. For the
less efficient extended access, the compiler loads the 16-bit index from the USE register
into register A, then converts it to a 32-bit index.
C–2
096254 Tandem Computers Incorporated
... Este manual também é adequado para os modelos :
Computadores - HP Integrity NonStop J-Series (397.39 kb)
Computadores - HP NonStop G-Series (397.39 kb)
Computadores - HP NonStop L-Series (397.39 kb)