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

[rrdtool.git] / src / hash_32.c

diff --git a/src/hash_32.c b/src/hash_32.c
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+++ b/src/hash_32.c
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+/*
+ * hash_32 - 32 bit Fowler/Noll/Vo hash code
+ *
+ *
+ ***
+ *
+ * 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 recommended 32 bit FNV-1 hash, pass FNV1_32_INIT as the
+ * Fnv32_t hashval argument to fnv_32_buf() or fnv_32_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!    :-)
+ */
+
+#include <stdlib.h>
+#include "fnv.h"
+
+
+/* 
+ * 32 bit magic FNV-0 and FNV-1 prime 
+ */
+#define FNV_32_PRIME ((Fnv32_t)0x01000193)     
+
+
+/*
+ * fnv_32_buf - perform a 32 bit Fowler/Noll/Vo hash on a buffer
+ *
+ * input:
+ *     buf     - start of buffer to hash
+ *     len     - length of buffer in octets
+ *     hval    - previous hash value or 0 if first call
+ *
+ * returns:
+ *     32 bit hash as a static hash type
+ *
+ * NOTE: To use the 32 bit FNV-0 historic hash, use FNV0_32_INIT as the hval
+ *      argument on the first call to either fnv_32_buf() or fnv_32_str().
+ *
+ * NOTE: To use the recommended 32 bit FNV-1 hash, use FNV1_32_INIT as the hval
+ *      argument on the first call to either fnv_32_buf() or fnv_32_str().
+ */
+Fnv32_t
+fnv_32_buf(void *buf, size_t len, Fnv32_t hval)
+{
+    unsigned char *bp = (unsigned char *)buf;  /* start of buffer */
+    unsigned char *be = bp + len;              /* beyond end of buffer */
+
+    /*
+     * FNV-1 hash each octet in the buffer
+     */
+    while (bp < be) {
+
+       /* multiply by the 32 bit FNV magic prime mod 2^64 */
+       hval *= FNV_32_PRIME;
+
+       /* xor the bottom with the current octet */
+       hval ^= (Fnv32_t)*bp++;
+    }
+
+    /* return our new hash value */
+    return hval;
+}
+
+
+/*
+ * fnv_32_str - perform a 32 bit Fowler/Noll/Vo hash on a string
+ *
+ * input:
+ *     str     - string to hash
+ *     hval    - previous hash value or 0 if first call
+ *
+ * returns:
+ *     32 bit hash as a static hash type
+ *
+ * NOTE: To use the 32 bit FNV-0 historic hash, use FNV0_32_INIT as the hval
+ *      argument on the first call to either fnv_32_buf() or fnv_32_str().
+ *
+ * NOTE: To use the recommended 32 bit FNV-1 hash, use FNV1_32_INIT as the hval
+ *      argument on the first call to either fnv_32_buf() or fnv_32_str().
+ */
+Fnv32_t
+fnv_32_str(char *str, Fnv32_t hval)
+{
+    unsigned char *s = (unsigned char *)str;   /* unsigned string */
+
+    /*
+     * FNV-1 hash each octet in the buffer
+     */
+    while (*s) {
+
+       /* multiply by the 32 bit FNV magic prime mod 2^64 */
+       hval *= FNV_32_PRIME;
+
+       /* xor the bottom with the current octet */
+       hval ^= (Fnv32_t)*s++;
+    }
+
+    /* return our new hash value */
+    return hval;
+}
+
+/* a wrapper function for fnv_32_str */
+unsigned long FnvHash(char *str)
+{
+  return fnv_32_str(str,FNV1_32_INIT);
+}