AIX Version 4.3 Differences Guide

1506-003 (S) Width of a bit-field of type "long" cannot exceed 64.
Bitfields are packed into the current word. Adjacent bitfields that cross a word
boundary will start at a new storage unit. This storage unit is a word in power, full
or natural alignment in 32-bit mode, but is a double word in 64-bit mode. In 64-bit
mode, adjacent declarations of bitfields of type long can now be contained into
one storage unit. Since long bitfields of greater than 32-bits were not permitted in
32-bit mode, this does not change and is not a portability problem.
Note that the packed alignment option just reduces the alignment ceiling to one,
two, four, or eight bytes depending on the packed=1|2|4|8 setting and leaves the
remaining alignment parameters unchanged.
3.3.1.4 Enum Support
Enum constants are always of type int, except when the range of these constants
is beyond the range of int, in which case, they have type unsigned int. Enum
variables may be smaller depending on the mode of -qenum=small|int|1|2|4|8
option.
small Specifies that enumeration occupies a minimum amount of storage
(either 1, 2, 4, or 8 bytes) depending on the range of enum constants.
int Enumeration occupies 4 bytes and are represented by int.
1 Enumeration occupies 1 byte and are represented by char.
2 Enumeration occupies 2 bytes and are represented by short.
4 Enumeration occupies 4 bytes and are represented by int.
8 Enumeration occupies 8 bytes and are represented by long.
enum=int and enum=4 are not the same. The enum=4 allows signed and
unsigned variant. The enum constants will usually be typed int, even in 64-bit
mode, to enhance compatibility with 32-bit programs. Only when the range
chooses an unsigned long or long, the constant will use unsigned long or long
types respectively. In 32-bit mode, -qenum=8 will yield an warning message:
1506-749 (W) Enum=8 is not valid in 32-bit mode, setting enum=4 instead.
3.3.2 XL Fortran Version 5
XL Fortran Version 5.1 introduced a new compiler option, -q64. This allows the
object code to run in 64-bit mode. The programming conventions are similar to C.
For a better understanding of Fortran tuning on POWER3 processors, see
RS/6000 Scientific and Technical Computing: POWER3 Introduction and Tuning
Guide, SG24-5155.
3.3.3 System Libraries
AIX 4.3 provides a 32-bit Application Binary Interface (ABI) and a 64-bit ABI. The
32-bit ABI consists of the entire pre-AIX 4.3 ABI and provides binary compatibility
at the same level as maintained by previous releases.
The dual ABI means two different version of all the Application Program
Interfaces (APIs). The mechanism for this are two separate versions of all the
objects in a given library. The objects are distinguished by distinct names. The
linker is able to distinguish which object to use for a given symbol based on the
differing object formats (32-bit and 64-bit).
64-Bit Enablement 61