1 /* 2 * This file was taken from http://ccodearchive.net/info/hash.html 3 * Changes to the original file include cleanups and removal of unwanted code 4 * and also code that depended on build_asert 5 */ 6 #ifndef CCAN_HASH_H 7 #define CCAN_HASH_H 8 #include <stdint.h> 9 #include <stdlib.h> 10 #include <endian.h> 11 12 /* Stolen mostly from: lookup3.c, by Bob Jenkins, May 2006, Public Domain. 13 * 14 * http://burtleburtle.net/bob/c/lookup3.c 15 */ 16 17 #ifdef __LITTLE_ENDIAN 18 # define HAVE_LITTLE_ENDIAN 1 19 #elif __BIG_ENDIAN 20 # define HAVE_BIG_ENDIAN 1 21 #else 22 #error Unknown endianness. Failure in endian.h 23 #endif 24 25 /** 26 * hash - fast hash of an array for internal use 27 * @p: the array or pointer to first element 28 * @num: the number of elements to hash 29 * @base: the base number to roll into the hash (usually 0) 30 * 31 * The memory region pointed to by p is combined with the base to form 32 * a 32-bit hash. 33 * 34 * This hash will have different results on different machines, so is 35 * only useful for internal hashes (ie. not hashes sent across the 36 * network or saved to disk). 37 * 38 * It may also change with future versions: it could even detect at runtime 39 * what the fastest hash to use is. 40 * 41 * See also: hash64, hash_stable. 42 * 43 * Example: 44 * #include <ccan/hash/hash.h> 45 * #include <err.h> 46 * #include <stdio.h> 47 * #include <string.h> 48 * 49 * // Simple demonstration: idential strings will have the same hash, but 50 * // two different strings will probably not. 51 * int main(int argc, char *argv[]) 52 * { 53 * uint32_t hash1, hash2; 54 * 55 * if (argc != 3) 56 * err(1, "Usage: %s <string1> <string2>", argv[0]); 57 * 58 * hash1 = __nl_hash(argv[1], strlen(argv[1]), 0); 59 * hash2 = __nl_hash(argv[2], strlen(argv[2]), 0); 60 * printf("Hash is %s\n", hash1 == hash2 ? "same" : "different"); 61 * return 0; 62 * } 63 */ 64 #define __nl_hash(p, num, base) nl_hash_any((p), (num)*sizeof(*(p)), (base)) 65 66 /* Our underlying operations. */ 67 uint32_t nl_hash_any(const void *key, size_t length, uint32_t base); 68 69 #endif /* HASH_H */ 70
