Setting Bitfields on big endian and little endian

[Ramesh]

Hi

I have a structure as below on big endian based system

typedef struct
{

unsigned long LedA:5;
unsigned long LedB:4;
unsigned long LedC:8;
unsigned long LedD:4;
unsigned long LedE:5;
unsigned long LedF:6;

}regs_t;

#define get_LedStatus(x) ((regs_t *)(&x))->LedA

main() {

unsigned long LedReg = 0x80000000;
printf("%X", get_LedStatus(LedReg))

}

On a big endian based system - I get a value of 0x1 as output.

For the little endian based system, I define the structure as below:

typedef struct
{

unsigned long LedF:6;
unsigned long LedE:5;
unsigned long LedD:4;
unsigned long LedC:8;
unsigned long LedB:4;
unsigned long LedA:5;

}regs_t;

I get a value as 0x10, so instead of getting a bit pattern like 0
0001
what I get is 1 0000

While reversing the bits solves the problem - Any insights as to what
could be the best solution if I have several such structures to be
ported from big endian to little endian system?

BTW the target is Linux 2.6 on x86 & gcc 4.12.2xxxx

Thanks
/R

[Malcolm McLean]

"Ramesh" <rr******@gmail.comwrote in message

While reversing the bits solves the problem - Any insights as to what
could be the best solution if I have several such structures to be
ported from big endian to little endian system?

If it matters where the bits are stored in memory, rip out the bitfields and
replace by an array of unsigned chars, with access functions to extract and
set the bits.

If it doesn't matter, and the motive for using a bitfield is to save memory,
you shouldn't need to do anything to port it.

--
Free games and programming goodies.
http://www.personal.leeds.ac.uk/~bgy1mm

[Gordon Burditt]

>I have a structure as below on big endian based system

Big-endian doesn't imply big-bit-endian and little-endian doesn't
imply little-bit-endian. There are 4 possibilities here.