lib: Adapt headers for use in C++.

[sliver-openvswitch.git] / lib / hash.h

diff --git a/lib/hash.h b/lib/hash.h
index 5485f8c..026eeda 100644 (file)
--- a/lib/hash.h
+++ b/lib/hash.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2008, 2009 Nicira Networks.
+ * Copyright (c) 2008, 2009, 2010 Nicira Networks.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -16,9 +16,15 @@
 #ifndef HASH_H
 #define HASH_H 1
 
+#include <stdbool.h>
 #include <stddef.h>
 #include <stdint.h>
 #include <string.h>
+#include "util.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
 
 /* This is the public domain lookup3 hash by Bob Jenkins from
  * http://burtleburtle.net/bob/c/lookup3.c, modified for style. */
@@ -47,6 +53,8 @@
     } while (0)
 
 uint32_t hash_words(const uint32_t *, size_t n_word, uint32_t basis);
+uint32_t hash_2words(uint32_t, uint32_t);
+uint32_t hash_3words(uint32_t, uint32_t, uint32_t);
 uint32_t hash_bytes(const void *, size_t n_bytes, uint32_t basis);
 
 static inline uint32_t hash_string(const char *s, uint32_t basis)
@@ -55,17 +63,57 @@ static inline uint32_t hash_string(const char *s, uint32_t basis)
 }
 
 /* This is Bob Jenkins' integer hash from
- * http://burtleburtle.net/bob/hash/integer.html, modified for style. */
+ * http://burtleburtle.net/bob/hash/integer.html, modified for style.
+ *
+ * This hash is faster than hash_2words(), but it isn't as good when 'basis' is
+ * important.  So use this function for speed or hash_2words() for hash
+ * quality. */
 static inline uint32_t hash_int(uint32_t x, uint32_t basis)
 {
     x -= x << 6;
     x ^= x >> 17;
     x -= x << 9;
     x ^= x << 4;
+    x += basis;
     x -= x << 3;
     x ^= x << 10;
     x ^= x >> 15;
-    return x + basis;
+    return x;
+}
+
+/* An attempt at a useful 1-bit hash function.  Has not been analyzed for
+ * quality. */
+static inline uint32_t hash_boolean(bool x, uint32_t basis)
+{
+    const uint32_t P0 = 0xc2b73583;   /* This is hash_int(1, 0). */
+    const uint32_t P1 = 0xe90f1258;   /* This is hash_int(2, 0). */
+    return (x ? P0 : P1) ^ HASH_ROT(basis, 1);
+}
+
+static inline uint32_t hash_double(double x, uint32_t basis)
+{
+    uint32_t value[2];
+    BUILD_ASSERT_DECL(sizeof x == sizeof value);
+
+    memcpy(value, &x, sizeof value);
+    return hash_3words(value[0], value[1], basis);
+}
+
+static inline uint32_t hash_pointer(const void *p, uint32_t basis)
+{
+    /* Often pointers are hashed simply by casting to integer type, but that
+     * has pitfalls since the lower bits of a pointer are often all 0 for
+     * alignment reasons.  It's hard to guess where the entropy really is, so
+     * we give up here and just use a high-quality hash function.
+     *
+     * The double cast suppresses a warning on 64-bit systems about casting to
+     * an integer to different size.  That's OK in this case, since most of the
+     * entropy in the pointer is almost certainly in the lower 32 bits. */
+    return hash_int((uint32_t) (uintptr_t) p, basis);
+}
+
+#ifdef __cplusplus
 }
+#endif
 
 #endif /* hash.h */