Re: Big and little indian valid in a byte??

[Ed L Cashin <ecashin@xxxxxxx>]

Jan Hudec <bulb@xxxxxx> writes:

> On Fri, Apr 30, 2004 at 14:37:59 +0530, syedk wrote:
>> Hi All,
>> 
>>      This is the structure declaration of IP Header. Can you tell me how 
>> little endian  and big endian come into picture in the case of  a 
>> byte.   U can find this declaration in 
>> /usr/src/linux-2.4.18-14/include/linux/ip.h.
>> 
>> struct iphdr {
>> #if defined(__LITTLE_ENDIAN_BITFIELD)
>>          __u8    ihl:4,
>>                  version:4;
>> #elif defined (__BIG_ENDIAN_BITFIELD)
>>          __u8    version:4,
>>                  ihl:4;
>
> You sure know, what the :4 modifier means. 

It seems like although it is just a feature of C, many people don't
know about bitfields.  It's part of the syntax for a bitfield -- four
bits in this case: a "nibble".

> So you should know, what's
> the difference between these two declaratinons. And thus know, what in
> the compiler is affected by endianity.

OP, note the order or the nibbles.

-- 
--Ed L Cashin            |   PGP public key:
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