Eric S. Raymond
esr at thyrsus.com
Tue Dec 13 02:06:48 UTC 2016
Hal Murray <hmurray at megapathdsl.net>:
> Disclaimer: I could easily get something backwards. I've worked with both
> and can easily switch even when I shouldn't.
> > +#define LAST32MASK 0x00000000ffffffffUL
> > +#define FIRST32MASK 0xffffffff00000000UL
> FIRST and LAST seem like poor choices for words. Do you mean first on the
> wire? Network protocols are almost always little endian.
> In any case, those masks are not within an ifdef so they will be used in both
> If you want the low or high bits, the masks and macros don't depend on the
> endianness if you are extracting from a uint64_t. You may need to invent a
> new host2net type macro to byte swap an 8 byte chunk if you want to
> send/receive those chunks from the network.
I found the problem a few hours ago.
There only needs to be one set of those macros, and it's the one that
I was thinking of as big-endian. That's because at the point at which
the data is in a uint64_t it's no longer in wire format; it has
already been word-swapped to host order.
Elementary, I know - but these things are easy for even the
experienced to get backwards, as you just demonstrated. Most network
protocols are *big-endian*, and NTP's are not an exception.
<a href="http://www.catb.org/~esr/">Eric S. Raymond</a>
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