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- Endian-ness
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- Endian-ness
- </h2></div></div></div><p>
- Atheros vendor-specific messages contain information in mixed endian format. The Ethernet header portion is sent <span class="emphasis"><em>big endian </em></span> but the Atheros header and payload are sent in <span class="emphasis"><em>little endian </em></span>. The traditional endian converstion functions <code class="function">htons()</code>, <code class="function">htonl()</code>, <code class="function">ntohs()</code> and <code class="function">ntohl()</code> can be used to perform platform independent conversions on the Ethernet header but not the Atheros header payload.
- </p><p>
- The Open Powerline Toolkit includes similar macros <code class="function">HTOLE16</code>, <code class="function">HTOLE32</code>, <code class="function">LE16TOH</code> and <code class="function">LE32TOH</code> in <a class="ulink" href="endian.h.html" target="_top">endian.h</a> which serve the same function but conform to recommendations for standarized byte order function on Linux, OpenBSD and FreeBSD. Observe that the names are independent of any network implications.
- </p><pre class="programlisting">
- #if BYTE_ORDER == BIG_ENDIAN
- # define LE16TOH(x) __bswap_16(x)
- # define LE32TOH(x) __bswap_32(x)
- # define LE64TOH(x) __bswap_64(x)
- # define HTOLE16(x) __bswap_16(x)
- # define HTOLE32(x) __bswap_32(x)
- # define HTOLE64(x) __bswap_64(x)
- #elif BYTE_ORDER == LITTLE_ENDIAN
- # define LE16TOH(x) (x)
- # define LE32TOH(x) (x)
- # define LE64TOH(x) (x)
- # define HTOLE16(x) (x)
- # define HTOLE32(x) (x)
- # define HTOLE64(x) (x)
- #else
- #error "Undefined host byte order."
- #endif
- </pre><p>
- In addition, the Open Powerline Toolkit includes function <a class="link" href="ch07s05.html#support-endian" title="endian">endian</a> that reverses byte order over a variable-length memory region.
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