Re: platform independent bit shifting

Andrew wrote:
) i'm trying to make sure my program runs on different platforms but don't
) have access to a big-endian system for testing.
)
) the only part of my code that might have anything to do with endianness
) is the part where i have to make sure the multibyte unsigned variables i
) write have the bytes in the proper order (either big-endian or
) little-endian, depending on the situation).
)
) so for example i'm concerned about the following function, is it
) platform-independent? it works on little-endian systems, but i can't
) find any information about whether bit shifting or the '& 0xFF' will
) produce the same results on big-endian systems.
)
) int write732(int image, unsigned value)
) {
) unsigned preparedValue;
)
) preparedValue = value & 0xFF;
) preparedValue <<= 8;
)
) preparedValue |= (value >> 8) & 0xFF;
) preparedValue <<= 8;
)
) preparedValue |= (value >> 16) & 0xFF;
) preparedValue <<= 8;
)
) preparedValue |= (value >> 24);
)
) return writeWrapper(image, &preparedValue, 4);
) }

This function reverses the bytes in the unsigned on both little-endian
and big-endian systems. Is that what you want ?

If not, you may want to look at the htonl() and ntohl() functions,
which are part of the standard C library, AFAIK.

By the way, the safest way to make your program endianess-independent is
to make sure that all operations that input and output bytes (to files or
to the network or whatever) work byte by byte.


SaSW, Willem
--
Disclaimer: I am in no way responsible for any of the statements
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drugged or something..
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#EOT
.