AIX endian again Post: 18027

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Top Forums UNIX for Advanced & Expert Users AIX endian again Post 18027 by Perderabo on Friday 22nd of March 2002 08:13:36 AM

03-22-2002

Administrator Emeritus

First, let's tackle TCP/IP and octets and integers. Not all computers have 8 bit bytes. Some weirdos have 6 bit bytes. I only one I know of is the CDC Cyber series, but I believe that there are more. Or were. Most everyone agrees on 8 bit bytes these days. But the designers of TCP/IP wanted it to work on all computers. They use the term octet as a politically correct term for an 8 bit quantity. TCP/IP does not deal with 8 octet integers. But it does have 2 octet integers which it called "short", and 4 octet integers which it calls "long". Both longs and shorts travel over the wire big-endian. But both are placed on the wire and extracted from it via macros. The macros are called ntohl, htonl, ntohs, and htons. (ntohl, for example, means network to host long). On hp-ux, just type "man htonl" to see a man page on them. These macros solve the problem of integers across a network. On a big-endian system like HP, they are just null macros and are removed by the pre-processor. On some other systems they expand into whatever is required.

It is obvious that this concept can be expanded in both directions. I would write new macros for 8 byte integers. And if I really needed it, I would write macros for bytes as well. It isn't hard to reverse the bits in a byte if that is truely required.

I have never worked with HDLC, and I just looked it up. I can't find proof of this, but I remain skeptical that it reverses its bytes. But if you are dumping data into the information frames with the bytes reversed, I guess that you are stuck with it.

Anyway, what is an application program doing using HDLC? HDLC is a level 2 protocol. That makes as much sense as an application program opening the ethernet device and writing its own ethernet frames. When you do stuff like that, it really starts to sound like you are talking to a directly attached device rather than using a network. Could you describe your network topology?

Perderabo

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LEARN ABOUT DEBIAN

be16toh

BYTEORDER(9)						   BSD Kernel Developer's Manual					      BYTEORDER(9)

NAME

     bswap16, bswap32, bswap64, be16toh, be32toh, be64toh, htobe16, htobe32, htobe64, htole16, htole32, htole64, le16toh, le32toh, le64toh,
     be16enc, be16dec, be32enc, be32dec, be64enc, be64dec, le16enc, le16dec, le32enc, le32dec, le64enc, le64dec -- byte order operations

SYNOPSIS

     #include <sys/endian.h>

     uint16_t
     bswap16(uint16_t int16);

     uint32_t
     bswap32(uint32_t int32);

     uint64_t
     bswap64(uint64_t int64);

     uint16_t
     be16toh(uint16_t big16);

     uint32_t
     be32toh(uint32_t big32);

     uint64_t
     be64toh(uint64_t big64);

     uint16_t
     htobe16(uint16_t host16);

     uint32_t
     htobe32(uint32_t host32);

     uint64_t
     htobe64(uint64_t host64);

     uint16_t
     htole16(uint16_t host16);

     uint32_t
     htole32(uint32_t host32);

     uint64_t
     htole64(uint64_t host64);

     uint16_t
     le16toh(uint16_t little16);

     uint32_t
     le32toh(uint32_t little32);

     uint64_t
     le64toh(uint64_t little64);

     uint16_t
     be16dec(const void *);

     uint32_t
     be32dec(const void *);

     uint64_t
     be64dec(const void *);

     uint16_t
     le16dec(const void *);

     uint32_t
     le32dec(const void *);

     uint64_t
     le64dec(const void *);

     void
     be16enc(void *, uint16_t);

     void
     be32enc(void *, uint32_t);

     void
     be64enc(void *, uint64_t);

     void
     le16enc(void *, uint16_t);

     void
     le32enc(void *, uint32_t);

     void
     le64enc(void *, uint64_t);

DESCRIPTION

     The bswap16(), bswap32(), and bswap64() functions return a byte order swapped integer.  On big endian systems, the number is converted to
     little endian byte order.	On little endian systems, the number is converted to big endian byte order.

     The be16toh(), be32toh(), and be64toh() functions return a big endian byte ordered integer converted to the system's native byte order.  The
     return value will be the same as the argument on big endian systems.

     The le16toh(), le32toh(), and le64toh() functions return a little endian byte ordered integer converted to the system's native byte order.
     The return value will be the same as the argument on little endian systems.

     The htobe16(), htobe32(), and htobe64() functions return a integer in the system's native byte order converted to big endian byte order.  The
     return value will be the same as the argument on big endian systems.

     The htole16(), htole32(), and htole64() functions return a integer in the system's native byte order converted to little endian byte order.
     The return value will be the same as the argument on little endian systems.

     The be16enc(), be16dec(), be32enc(), be32dec(), be64enc(), be64dec(), le16enc(), le16dec(), le32enc(), le32dec(), le64enc(), and le64dec()
     functions encode and decode integers to/from byte strings on any alignment in big/little endian format.

SEE ALSO

     byteorder(3)

HISTORY

     The hto*() and toh*() functions first appeared in FreeBSD 5.0, and were originally developed by the NetBSD project.

     The encode/decode functions first appeared in FreeBSD 5.1.

BSD
								  April 29, 2002							       BSD