lib/hash.h

   1 /*
   2  * Copyright (c) 2008, 2009, 2010, 2012, 2013 Nicira, Inc.
   3  *
   4  * Licensed under the Apache License, Version 2.0 (the "License");
   5  * you may not use this file except in compliance with the License.
   6  * You may obtain a copy of the License at:
   7  *
   8  *     http://www.apache.org/licenses/LICENSE-2.0
   9  *
  10  * Unless required by applicable law or agreed to in writing, software
  11  * distributed under the License is distributed on an "AS IS" BASIS,
  12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  13  * See the License for the specific language governing permissions and
  14  * limitations under the License.
  15  */
  16 #ifndef HASH_H
  17 #define HASH_H 1
  18
  19 #include <stdbool.h>
  20 #include <stddef.h>
  21 #include <stdint.h>
  22 #include <string.h>
  23 #include "util.h"
  24
  25 #ifdef __cplusplus
  26 extern "C" {
  27 #endif
  28
  29 static inline uint32_t
  30 hash_rot(uint32_t x, int k)
  31 {
  32     return (x << k) | (x >> (32 - k));
  33 }
  34
  35 uint32_t hash_words(const uint32_t data[], size_t n_words, uint32_t basis);
  36 uint32_t hash_bytes(const void *, size_t n_bytes, uint32_t basis);
  37
  38 static inline uint32_t hash_int(uint32_t x, uint32_t basis);
  39 static inline uint32_t hash_2words(uint32_t, uint32_t);
  40 static inline uint32_t hash_uint64(uint64_t);
  41 uint32_t hash_3words(uint32_t, uint32_t, uint32_t);
  42
  43 static inline uint32_t hash_boolean(bool x, uint32_t basis);
  44 uint32_t hash_double(double, uint32_t basis);
  45
  46 static inline uint32_t hash_pointer(const void *, uint32_t basis);
  47 static inline uint32_t hash_string(const char *, uint32_t basis);
  48
  49 /* Murmurhash by Austin Appleby,
  50  * from http://code.google.com/p/smhasher/source/browse/trunk/MurmurHash3.cpp.
  51  *
  52  * The upstream license there says:
  53  *
  54  * // MurmurHash3 was written by Austin Appleby, and is placed in the public
  55  * // domain. The author hereby disclaims copyright to this source code.
  56  *
  57  * See hash_words() for sample usage. */
  58
  59 static inline uint32_t mhash_add__(uint32_t hash, uint32_t data)
  60 {
  61     data *= 0xcc9e2d51;
  62     data = hash_rot(data, 15);
  63     data *= 0x1b873593;
  64     return hash ^ data;
  65 }
  66
  67 static inline uint32_t mhash_add(uint32_t hash, uint32_t data)
  68 {
  69     hash = mhash_add__(hash, data);
  70     hash = hash_rot(hash, 13);
  71     return hash * 5 + 0xe6546b64;
  72 }
  73
  74 static inline uint32_t mhash_finish(uint32_t hash, size_t n_bytes)
  75 {
  76     hash ^= n_bytes;
  77     hash ^= hash >> 16;
  78     hash *= 0x85ebca6b;
  79     hash ^= hash >> 13;
  80     hash *= 0xc2b2ae35;
  81     hash ^= hash >> 16;
  82     return hash;
  83 }
  84
  85 static inline uint32_t hash_string(const char *s, uint32_t basis)
  86 {
  87     return hash_bytes(s, strlen(s), basis);
  88 }
  89
  90 static inline uint32_t hash_int(uint32_t x, uint32_t basis)
  91 {
  92     return hash_2words(x, basis);
  93 }
  94
  95 /* An attempt at a useful 1-bit hash function.  Has not been analyzed for
  96  * quality. */
  97 static inline uint32_t hash_boolean(bool x, uint32_t basis)
  98 {
  99     const uint32_t P0 = 0xc2b73583;   /* This is hash_int(1, 0). */
 100     const uint32_t P1 = 0xe90f1258;   /* This is hash_int(2, 0). */
 101     return (x ? P0 : P1) ^ hash_rot(basis, 1);
 102 }
 103
 104 static inline uint32_t hash_pointer(const void *p, uint32_t basis)
 105 {
 106     /* Often pointers are hashed simply by casting to integer type, but that
 107      * has pitfalls since the lower bits of a pointer are often all 0 for
 108      * alignment reasons.  It's hard to guess where the entropy really is, so
 109      * we give up here and just use a high-quality hash function.
 110      *
 111      * The double cast suppresses a warning on 64-bit systems about casting to
 112      * an integer to different size.  That's OK in this case, since most of the
 113      * entropy in the pointer is almost certainly in the lower 32 bits. */
 114     return hash_int((uint32_t) (uintptr_t) p, basis);
 115 }
 116
 117 static inline uint32_t hash_2words(uint32_t x, uint32_t y)
 118 {
 119     return mhash_finish(mhash_add(mhash_add(x, 0), y), 8);
 120 }
 121
 122 static inline uint32_t hash_uint64(const uint64_t x)
 123 {
 124     return hash_2words((uint32_t)(x >> 32), (uint32_t)x);
 125 }
 126
 127 #ifdef __cplusplus
 128 }
 129 #endif
 130
 131 #endif /* hash.h */