--- /dev/null
+#ifndef CCAN_HASH_H
+#define CCAN_HASH_H
+#include <stdint.h>
+#include <stdlib.h>
+#include "config.h"
+
+/* Stolen mostly from: lookup3.c, by Bob Jenkins, May 2006, Public Domain.
+ *
+ * http://burtleburtle.net/bob/c/lookup3.c
+ */
+
+/**
+ * hash - fast hash of an array for internal use
+ * @p: the array or pointer to first element
+ * @num: the number of elements to hash
+ * @base: the base number to roll into the hash (usually 0)
+ *
+ * The memory region pointed to by p is combined with the base to form
+ * a 32-bit hash.
+ *
+ * This hash will have different results on different machines, so is
+ * only useful for internal hashes (ie. not hashes sent across the
+ * network or saved to disk).
+ *
+ * It may also change with future versions: it could even detect at runtime
+ * what the fastest hash to use is.
+ *
+ * See also: hash_stable.
+ *
+ * Example:
+ * #include "hash/hash.h"
+ * #include <err.h>
+ * #include <stdio.h>
+ *
+ * // Simple demonstration: idential strings will have the same hash, but
+ * // two different strings will probably not.
+ * int main(int argc, char *argv[])
+ * {
+ * uint32_t hash1, hash2;
+ *
+ * if (argc != 3)
+ * err(1, "Usage: %s <string1> <string2>", argv[0]);
+ *
+ * hash1 = hash(argv[1], strlen(argv[1]), 0);
+ * hash2 = hash(argv[2], strlen(argv[2]), 0);
+ * printf("Hash is %s\n", hash1 == hash2 ? "same" : "different");
+ * return 0;
+ * }
+ */
+#define hash(p, num, base) hash_any((p), (num)*sizeof(*(p)), (base))
+
+/**
+ * hash_stable - hash of an array for external use
+ * @p: the array or pointer to first element
+ * @num: the number of elements to hash
+ * @base: the base number to roll into the hash (usually 0)
+ *
+ * The memory region pointed to by p is combined with the base to form
+ * a 32-bit hash.
+ *
+ * This hash will have the same results on different machines, so can
+ * be used for external hashes (ie. not hashes sent across the network
+ * or saved to disk). The results will not change in future versions
+ * of this package.
+ *
+ * Example:
+ * #include "hash/hash.h"
+ * #include <err.h>
+ * #include <stdio.h>
+ *
+ * int main(int argc, char *argv[])
+ * {
+ * if (argc != 2)
+ * err(1, "Usage: %s <string-to-hash>", argv[0]);
+ *
+ * printf("Hash stable result is %u\n",
+ * hash_stable(argv[1], strlen(argv[1]), 0));
+ * return 0;
+ * }
+ */
+#define hash_stable(p, num, base) \
+ hash_any_stable((p), (num)*sizeof(*(p)), (base))
+
+/**
+ * hash_u32 - fast hash an array of 32-bit values for internal use
+ * @key: the array of uint32_t
+ * @num: the number of elements to hash
+ * @base: the base number to roll into the hash (usually 0)
+ *
+ * The array of uint32_t pointed to by @key is combined with the base
+ * to form a 32-bit hash. This is 2-3 times faster than hash() on small
+ * arrays, but the advantage vanishes over large hashes.
+ *
+ * This hash will have different results on different machines, so is
+ * only useful for internal hashes (ie. not hashes sent across the
+ * network or saved to disk).
+ */
+uint32_t hash_u32(const uint32_t *key, size_t num, uint32_t base);
+
+/* Our underlying operations. */
+uint32_t hash_any(const void *key, size_t length, uint32_t base);
+uint32_t hash_any_stable(const void *key, size_t length, uint32_t base);
+
+/**
+ * hash_pointer - hash a pointer for internal use
+ * @p: the pointer value to hash
+ * @base: the base number to roll into the hash (usually 0)
+ *
+ * The pointer p (not what p points to!) is combined with the base to form
+ * a 32-bit hash.
+ *
+ * This hash will have different results on different machines, so is
+ * only useful for internal hashes (ie. not hashes sent across the
+ * network or saved to disk).
+ *
+ * Example:
+ * #include "hash/hash.h"
+ *
+ * // Code to keep track of memory regions.
+ * struct region {
+ * struct region *chain;
+ * void *start;
+ * unsigned int size;
+ * };
+ * // We keep a simple hash table.
+ * static struct region *region_hash[128];
+ *
+ * static void add_region(struct region *r)
+ * {
+ * unsigned int h = hash_pointer(r->start);
+ *
+ * r->chain = region_hash[h];
+ * region_hash[h] = r->chain;
+ * }
+ *
+ * static void find_region(const void *start)
+ * {
+ * struct region *r;
+ *
+ * for (r = region_hash[hash_pointer(start)]; r; r = r->chain)
+ * if (r->start == start)
+ * return r;
+ * return NULL;
+ * }
+ */
+static inline uint32_t hash_pointer(const void *p, uint32_t base)
+{
+ if (sizeof(p) % sizeof(uint32_t) == 0) {
+ /* This convoluted union is the right way of aliasing. */
+ union {
+ uint32_t u32[sizeof(p) / sizeof(uint32_t)];
+ const void *p;
+ } u;
+ u.p = p;
+ return hash_u32(u.u32, sizeof(p) / sizeof(uint32_t), base);
+ }
+ return hash(&p, 1, base);
+}
+#endif /* HASH_H */
projects / ccan / blobdiff