Import of OpenBSD's sys/sys/hash.h providing generic 32bit hash functions.

Requested by:	flz (to port Open[BGP|OSPF]D)
MFC after:	3 days

sys/sys/hash.h

@@ -0,0 +1,128 @@
+/*-
+ * Copyright (c) 2001 Tobias Weingartner
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+ * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+ * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ * $OpenBSD: hash.h,v 1.4 2004/05/25 18:37:23 jmc Exp $
+ * $FreeBSD$
+ */
+
+#ifndef _SYS_HASH_H_
+#define	_SYS_HASH_H_
+#include <sys/types.h>
+
+/*
+ * Note: SMALL_KERNEL might be used to shrink these, right now I
+ * do not see the point, as my kernel did not grow appreciably when
+ * I switched to these from other inline code.  This may have to be
+ * revisited when/if these functions become more prevalent in the
+ * kernel.
+ */
+
+/* Convenience */
+#ifndef	HASHINIT
+#define	HASHINIT	5381
+#define	HASHSTEP(x,c)	(((x << 5) + x) + (c))
+#endif
+
+/*
+ * Return a 32-bit hash of the given buffer.  The init
+ * value should be 0, or the previous hash value to extend
+ * the previous hash.
+ */
+static __inline uint32_t
+hash32_buf(const void *buf, size_t len, uint32_t hash)
+{
+	const unsigned char *p = buf;
+
+	while (len--)
+		hash = HASHSTEP(hash, *p++);
+
+	return hash;
+}
+
+/*
+ * Return a 32-bit hash of the given string.
+ */
+static __inline uint32_t
+hash32_str(const void *buf, uint32_t hash)
+{
+	const unsigned char *p = buf;
+
+	while (*p)
+		hash = HASHSTEP(hash, *p++);
+
+	return hash;
+}
+
+/*
+ * Return a 32-bit hash of the given string, limited by N.
+ */
+static __inline uint32_t
+hash32_strn(const void *buf, size_t len, uint32_t hash)
+{
+	const unsigned char *p = buf;
+
+	while (*p && len--)
+		hash = HASHSTEP(hash, *p++);
+
+	return hash;
+}
+
+/*
+ * Return a 32-bit hash of the given string terminated by C,
+ * (as well as 0).  This is mainly here as a helper for the
+ * namei() hashing of path name parts.
+ */
+static __inline uint32_t
+hash32_stre(const void *buf, int end, char **ep, uint32_t hash)
+{
+	const unsigned char *p = buf;
+
+	while (*p && (*p != end))
+		hash = HASHSTEP(hash, *p++);
+
+	if (ep)
+		*ep = (char *)p;
+
+	return hash;
+}
+
+/*
+ * Return a 32-bit hash of the given string, limited by N,
+ * and terminated by C (as well as 0).  This is mainly here
+ * as a helper for the namei() hashing of path name parts.
+ */
+static __inline uint32_t
+hash32_strne(const void *buf, size_t len, int end, char **ep, uint32_t hash)
+{
+	const unsigned char *p = buf;
+
+	while (*p && (*p != end) && len--)
+		hash = HASHSTEP(hash, *p++);
+
+	if (ep)
+		*ep = (char *)p;
+
+	return hash;
+}
+#endif /* !_SYS_HASH_H_ */