macro BITS_BIG_ENDIAN

[James E Wilson]

Sivan Balaji wrote:
> I have been through GCC internals documentation and I am not clear about 
> BITS_BIG_ENDIAN. does BITS_BIG_ENDIAN related to the order of bit field 
> members allocation.

There is no way to control the order of bit-field allocation. 
Bit-fields are always assigned to the first available bit, possibly 
constrained by other factors, such as alignment.  That means that they 
start at the low order bit for little-endian, and the high order bit for 
big-endian.  This is the "right" way to do things.  It is very unusual 
for a compiler to do this differently.

The only thing controlled by BITS_BIG_ENDIAN is the bit numbering used 
for bit-field instructions.  Or more specifically, it controls how the 
operands to ZERO_EXTRACT and SIGN_EXTRACT RTL operators are interpreted. 
  It has no other effect.

Apparently, Red Hat has patches that allow one to switch the order of 
bit-field allocation, but these patches have not been contributed.
-- 
Jim Wilson, GNU Tools Support, http://www.SpecifixInc.com