Aberrant Behavior Detection support. A brief overview added to rrdtool.pod.

[rrdtool.git] / src / fnv.h

diff --git a/src/fnv.h b/src/fnv.h
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+/*
+ * fnv - Fowler/Noll/Vo- hash code
+ *
+ * @(#) $Revision$
+ * @(#) $Id$
+ * @(#) $Source$
+ *
+ ***
+ *
+ * Fowler/Noll/Vo- hash
+ *
+ * The basis of this hash algorithm was taken from an idea sent
+ * as reviewer comments to the IEEE POSIX P1003.2 committee by:
+ *
+ *      Phong Vo (http://www.research.att.com/info/kpv/)
+ *      Glenn Fowler (http://www.research.att.com/~gsf/)
+ *
+ * In a subsequent ballot round:
+ *
+ *      Landon Curt Noll (http://reality.sgi.com/chongo/)
+ *
+ * improved on their algorithm.  Some people tried this hash
+ * and found that it worked rather well.  In an EMail message
+ * to Landon, they named it the ``Fowler/Noll/Vo'' or FNV hash.
+ *
+ * FNV hashes are architected to be fast while maintaining a low
+ * collision rate. The FNV speed allows one to quickly hash lots
+ * of data while maintaining a reasonable collision rate.  See:
+ *
+ *      http://reality.sgi.com/chongo/tech/comp/fnv/
+ *
+ * for more details as well as other forms of the FNV hash.
+ *
+ ***
+ *
+ * NOTE: The FNV-0 historic hash is not recommended.  One should use
+ *      the FNV-1 hash instead.
+ *
+ * To use the 32 bit FNV-0 historic hash, pass FNV0_32_INIT as the
+ * Fnv32_t hashval argument to fnv_32_buf() or fnv_32_str().
+ *
+ * To use the 64 bit FNV-0 historic hash, pass FNV0_64_INIT as the
+ * Fnv64_t hashval argument to fnv_64_buf() or fnv_64_str().
+ *
+ * To use the recommended 32 bit FNV-1 hash, pass FNV1_32_INIT as the
+ * Fnv32_t hashval argument to fnv_32_buf() or fnv_32_str().
+ *
+ * To use the recommended 64 bit FNV-1 hash, pass FNV1_64_INIT as the
+ * Fnv64_t hashval argument to fnv_64_buf() or fnv_64_str().
+ *
+ ***
+ *
+ * Please do not copyright this code.  This code is in the public domain.
+ *
+ * LANDON CURT NOLL DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
+ * INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO
+ * EVENT SHALL LANDON CURT NOLL BE LIABLE FOR ANY SPECIAL, INDIRECT OR
+ * CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF
+ * USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
+ * OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+ * PERFORMANCE OF THIS SOFTWARE.
+ *
+ * By:
+ *     chongo <Landon Curt Noll> /\oo/\
+ *     http://reality.sgi.com/chongo/
+ *     EMail: chongo_fnv at prime dot engr dot sgi dot com
+ *
+ * Share and Enjoy!    :-)
+ */
+
+#if !defined(__FNV_H__)
+#define __FNV_H__
+
+
+/*
+ * 32 bit FNV-0 hash type
+ */
+typedef unsigned long Fnv32_t;
+
+
+/* 
+ * 32 bit FNV-0 zero initial basis
+ *
+ * This historic hash is not recommended.  One should use
+ * the FNV-1 hash and inital basis instead.
+ */
+#define FNV0_32_INIT ((Fnv32_t)0)
+
+
+/*
+ * 32 bit FNV-1 non-zero initial basis
+ *
+ * The FNV-1 initial basis is the FNV-0 hash of the following 32 octets:
+ *
+ *              chongo <Landon Curt Noll> /\../\
+ *
+ * Note that the \'s above are not back-slashing escape characters.
+ * They are literal ASCII  backslash 0x5c characters.
+ */
+#define FNV1_32_INIT ((Fnv32_t)0x811c9dc5)
+
+#endif /* __FNV_H__ */