Bit order == byte order??

Erik Trulsson ertr1013 at
Thu Mar 3 21:03:34 UTC 2011

On Thu, Mar 03, 2011 at 11:26:12AM -0500, Frank Solensky wrote:
> In sys/netinet/ip.h, the first octet of the ip header structure tests
> the byte ordering to determine the ordering of the header length
> (ip_hl) and version (ip_v) fields.
> My question: that always works?  While my reading of the language
> specification document leaves both the ordering of the bits within a
> byte and the bytes within a longer field as implementation choices,
> the two are independent of each other.
> I haven't run into a CPU where this assumption was proven incorrect.
> It just surprised me to see that recently

Unless you have a CPU where memory is addressed bit-by-bit rather than
byte-by-byte the ordering of bits within a byte is not only completely
irrelevant, it is also pretty much impossible to determine

<Insert your favourite quote here.>
Erik Trulsson
ertr1013 at

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