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This section discusses storage sizes and alignment modes for
the HP 9000 and HP Apollo systems as well as the VAX/VMS C, CCS/1000,
and CCS/C 3000. In all, there are a total of seven possible alignment modes
which can be grouped into five categories as described in Table 2-1 “The Alignment Modes ”. Table 2-1 The Alignment Modes Alignment Mode | Description |
|---|
HPUX_WORD,
DOMAIN_WORD | HPUX_WORD
is the native alignment for HP 9000 Series 300 and 400. DOMAIN_WORD
is the native alignment for HP Apollo Series 3000 and 4000. The
most restricted alignment boundary for a structure member is 2 bytes. | HPUX_NATURAL,
DOMAIN_NATURAL | HPUX_NATURAL
is the native alignment for HP 9000 workstations and servers and
HP 3000 Series 900 and, therefore, is the default alignment mode.
DOMAIN_NATURAL
is the native alignment for HP Apollo Series 10000. The alignment
of a structure member is related to its size (except for long double
and long pointers), and the most restricted alignment boundary is
8 bytes. | HPUX_NATURAL_S500 | HPUX_NATURAL_S500
is the native alignment for HP 9000 Series 500. The alignment of
a structure member is related to its size, and the most restricted
alignment boundary is 4 bytes. | NATURAL | NATURAL
is an architecture-independent alignment mode for HP Series 300,
400, workstations and servers, and HP Apollo Series 3000, 4000,
and 10000. In the NATURAL
mode, alignment of a structure member is related to its size, the
most restricted alignment boundary being 8 bytes. The difference
between HPUX_NATURAL
and NATURAL are
a 1-byte versus 2-byte minimum structure alignment and size, and
the bit-field rules. This alignment mode is recommended when portability
is an issue, since this mode enables data to be shared among the
greatest number of HP-UX and Domain (HP Apollo) systems. | NOPADDING | This mode does not arise from a particular
architecture. The most restricted alignment is 1 byte. NOPADDING
alignment causes all structure and union members and typedefs to
be packed on a byte boundary, and ensures that there will be no
full byte padding inside the structure. Bit-field members either
are byte-aligned or aligned immediately following a previous bit-field
member, except in rare cases described in the section "Alignments
of Bit-Fields" below. |
| | | |  | NOTE: With the exception of bit-fields, DOMAIN_WORD
structure alignment is the same as HPUX_WORD
structure alignment, and DOMAIN_NATURAL
structure alignment is the same as HP_NATURAL
structure alignment. | | | | |
The alignment modes listed above can be controlled using the
HP_ALIGN compiler
pragma. See “The HP_ALIGN Pragma ”
for a detailed description of this pragma. The NATURAL
alignment mode should be used whenever possible. This mode enables
data to be shared among the greatest number of HP-UX and Domain
(HP Apollo) systems. |
