MACRO, /MIGRATION, Page-Related Calculations
*Conan The Librarian (sorry for the slow response - running on an old VAX)
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/sys$common/syshlp/helplib.hlb MACRO, /MIGRATION, Page-Related Calculations *Conan The Librarian (sorry for the slow response - running on an old VAX) |
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This section describes the following macros that provide a
standard, architecture-independent means for calculating page-
size dependent values:
o $BYTES_TO_PAGES
o $NEXT_PAGE
o $PAGES_TO_BYTES
o $PREVIOUS_PAGE
o $ROUND_RETADR
o $START_OF_PAGE
These macros reside in the directory SYS$LIBRARY:STARLET.MLB and
can be used by both application code and system code. Because
application code does not have access to SYSTEM_DATA_CELLS, the
user must supply the relevant masks, shift values, and so on.
The shift values are correlated with the page size of the
processor. The rightshift values are negative; the leftshift
values are positive, as shown in the following table.
Page size rightshift leftshift
512 bytes (VAX) -9 9
8K (Alpha) -13 13
Typically, the application issues a call to $GETSYI (specifying
the SYI$_PAGESIZE item descriptor) to obtain the CPU-specific
page size and then compute other values from the page size that
is returned.
The following conventions apply to the macros described in this
section:
o If the destination operand is blank, the source operand is
used as the destination.
o All macros conditionalize code on the symbols VAXPAGE and
BIGPAGE.
o Several macros allow for page-size-independent code on VAX
systems with the independent=YES argument. These macros
generate code in which I-stream fetches are changed to memory
accesses. Because this is inherently slower on a VAX system,
the default value of the independent argument is NO.
Additional Information (explode) :
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