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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,

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