2 * Copyright (c) 2009, 2012, 2014, 2015 Nicira, Inc.
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:
8 * http://www.apache.org/licenses/LICENSE-2.0
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.
29 set_bit(uint32_t array[3], int bit)
31 assert(bit >= 0 && bit <= 96);
32 memset(array, 0, sizeof(uint32_t) * 3);
34 array[bit / 32] = UINT32_C(1) << (bit % 32);
38 /* When bit == n_bits, the function just 0 sets the 'values'. */
40 set_bit128(ovs_u128 *values, int bit, int n_bits)
42 assert(bit >= 0 && bit <= 2048);
43 memset(values, 0, n_bits/8);
48 values[bit / 128].u64.lo = UINT64_C(1) << (b % 64);
50 values[bit / 128].u64.hi = UINT64_C(1) << (b % 64);
56 get_range128(ovs_u128 *value, int ofs, uint64_t mask)
58 return ((ofs < 64 ? (value->u64.lo >> ofs) : 0) & mask)
59 | ((ofs <= 64 ? (value->u64.hi << (64 - ofs)) : (value->u64.hi >> (ofs - 64)) & mask));
63 hash_words_cb(uint32_t input)
65 return hash_words(&input, 1, 0);
69 jhash_words_cb(uint32_t input)
71 return jhash_words(&input, 1, 0);
75 hash_int_cb(uint32_t input)
77 return hash_int(input, 0);
81 check_word_hash(uint32_t (*hash)(uint32_t), const char *name,
86 for (i = 0; i <= 32; i++) {
87 uint32_t in1 = i < 32 ? UINT32_C(1) << i : 0;
88 for (j = i + 1; j <= 32; j++) {
89 uint32_t in2 = j < 32 ? UINT32_C(1) << j : 0;
90 uint32_t out1 = hash(in1);
91 uint32_t out2 = hash(in2);
92 const uint32_t unique_mask = (UINT32_C(1) << min_unique) - 1;
94 for (ofs = 0; ofs < 32 - min_unique; ofs++) {
95 uint32_t bits1 = (out1 >> ofs) & unique_mask;
96 uint32_t bits2 = (out2 >> ofs) & unique_mask;
98 printf("Partial collision for '%s':\n", name);
99 printf("%s(%08"PRIx32") = %08"PRIx32"\n", name, in1, out1);
100 printf("%s(%08"PRIx32") = %08"PRIx32"\n", name, in2, out2);
101 printf("%d bits of output starting at bit %d "
102 "are both 0x%"PRIx32"\n", min_unique, ofs, bits1);
110 check_3word_hash(uint32_t (*hash)(const uint32_t[], size_t, uint32_t),
115 for (i = 0; i <= 96; i++) {
116 for (j = i + 1; j <= 96; j++) {
117 uint32_t in0[3], in1[3], in2[3];
118 uint32_t out0,out1, out2;
119 const int min_unique = 12;
120 const uint32_t unique_mask = (UINT32_C(1) << min_unique) - 1;
125 out0 = hash(in0, 3, 0);
126 out1 = hash(in1, 3, 0);
127 out2 = hash(in2, 3, 0);
130 printf("%s hash not the same for non-64 aligned data "
131 "%08"PRIx32" != %08"PRIx32"\n", name, out0, out1);
133 if ((out1 & unique_mask) == (out2 & unique_mask)) {
134 printf("%s has a partial collision:\n", name);
135 printf("hash(1 << %d) == %08"PRIx32"\n", i, out1);
136 printf("hash(1 << %d) == %08"PRIx32"\n", j, out2);
137 printf("The low-order %d bits of output are both "
138 "0x%"PRIx32"\n", min_unique, out1 & unique_mask);
145 check_hash_bytes128(void (*hash)(const void *, size_t, uint32_t, ovs_u128 *),
146 const char *name, const int min_unique)
148 const uint64_t unique_mask = (UINT64_C(1) << min_unique) - 1;
149 const int n_bits = sizeof(ovs_u128) * 8;
152 for (i = 0; i <= n_bits; i++) {
153 OVS_PACKED(struct offset_ovs_u128 {
161 set_bit128(in0, i, n_bits);
162 set_bit128(&in1, i, n_bits);
163 hash(in0, sizeof(ovs_u128), 0, &out0);
164 hash(&in1, sizeof(ovs_u128), 0, &out1);
165 if (!ovs_u128_equals(&out0, &out1)) {
166 printf("%s hash not the same for non-64 aligned data "
167 "%016"PRIx64"%016"PRIx64" != %016"PRIx64"%016"PRIx64"\n",
168 name, out0.u64.lo, out0.u64.hi, out1.u64.lo, out1.u64.hi);
171 for (j = i + 1; j <= n_bits; j++) {
176 set_bit128(&in2, j, n_bits);
177 hash(&in2, sizeof(ovs_u128), 0, &out2);
178 for (ofs = 0; ofs < 128 - min_unique; ofs++) {
179 uint64_t bits1 = get_range128(&out1, ofs, unique_mask);
180 uint64_t bits2 = get_range128(&out2, ofs, unique_mask);
182 if (bits1 == bits2) {
183 printf("%s has a partial collision:\n", name);
184 printf("hash(1 << %d) == %016"PRIx64"%016"PRIx64"\n",
185 i, out1.u64.hi, out1.u64.lo);
186 printf("hash(1 << %d) == %016"PRIx64"%016"PRIx64"\n",
187 j, out2.u64.hi, out2.u64.lo);
188 printf("%d bits of output starting at bit %d "
189 "are both 0x%016"PRIx64"\n", min_unique, ofs, bits1);
197 check_256byte_hash(void (*hash)(const void *, size_t, uint32_t, ovs_u128 *),
198 const char *name, const int min_unique)
200 const uint64_t unique_mask = (UINT64_C(1) << min_unique) - 1;
201 const int n_bits = sizeof(ovs_u128) * 8 * 16;
204 for (i = 0; i <= n_bits; i++) {
205 OVS_PACKED(struct offset_ovs_u128 {
209 ovs_u128 *in0, in1[16];
213 set_bit128(in0, i, n_bits);
214 set_bit128(in1, i, n_bits);
215 hash(in0, sizeof(ovs_u128) * 16, 0, &out0);
216 hash(in1, sizeof(ovs_u128) * 16, 0, &out1);
217 if (!ovs_u128_equals(&out0, &out1)) {
218 printf("%s hash not the same for non-64 aligned data "
219 "%016"PRIx64"%016"PRIx64" != %016"PRIx64"%016"PRIx64"\n",
220 name, out0.u64.lo, out0.u64.hi, out1.u64.lo, out1.u64.hi);
223 for (j = i + 1; j <= n_bits; j++) {
227 set_bit128(in2, j, n_bits);
228 hash(in2, sizeof(ovs_u128) * 16, 0, &out2);
229 if ((out1.u64.lo & unique_mask) == (out2.u64.lo & unique_mask)) {
230 printf("%s has a partial collision:\n", name);
231 printf("hash(1 << %4d) == %016"PRIx64"%016"PRIx64"\n", i,
232 out1.u64.hi, out1.u64.lo);
233 printf("hash(1 << %4d) == %016"PRIx64"%016"PRIx64"\n", j,
234 out2.u64.hi, out2.u64.lo);
235 printf("The low-order %d bits of output are both "
236 "0x%"PRIx64"\n", min_unique, out1.u64.lo & unique_mask);
243 test_hash_main(int argc OVS_UNUSED, char *argv[] OVS_UNUSED)
246 * The following tests check that all hashes computed with hash_function
247 * with one 1-bit (or no 1-bits) set within a X-bit word have different
248 * values in all N-bit consecutive comparisons.
250 * test_function(hash_function, test_name, N)
252 * Given a random distribution, the probability of at least one collision
253 * in any set of N bits is approximately
255 * 1 - (prob of no collisions)
256 * **(combination of all possible comparisons)
257 * == 1 - ((2**N - 1)/2**N)**C(X+1,2)
260 * There are (X-N) ways to pick N consecutive bits in a X-bit word, so if we
261 * assumed independence then the chance of having no collisions in any of
262 * those X-bit runs would be (1-p)**(X-N) == q. If this q is very small
263 * and we can also find a relatively small 'magic number' N such that there
264 * is no collision in any comparison, then it means we have a pretty good
267 * The values of each parameters mentioned above for the tested hash
268 * functions are summarized as follow:
270 * hash_function X N p q
271 * ------------- --- --- ------- -------
273 * hash_words_cb 32 11 0.22 0.0044
274 * jhash_words_cb 32 11 0.22 0.0044
275 * hash_int_cb 32 12 0.12 0.0078
276 * hash_bytes128 128 19 0.0156 0.174
279 check_word_hash(hash_words_cb, "hash_words", 11);
280 check_word_hash(jhash_words_cb, "jhash_words", 11);
281 check_word_hash(hash_int_cb, "hash_int", 12);
282 check_hash_bytes128(hash_bytes128, "hash_bytes128", 19);
285 * The following tests check that all hashes computed with hash_function
286 * with one 1-bit (or no 1-bits) set within Y X-bit word have different
287 * values in their lowest N bits.
289 * test_function(hash_function, test_name, N)
291 * Given a random distribution, the probability of at least one collision
292 * in any set of N bits is approximately
294 * 1 - (prob of no collisions)
295 * **(combination of all possible comparisons)
296 * == 1 - ((2**N - 1)/2**N)**C(Y*X+1,2)
299 * If this p is not very small and we can also find a relatively small
300 * 'magic number' N such that there is no collision in any comparison,
301 * then it means we have a pretty good hash function.
303 * The values of each parameters mentioned above for the tested hash
304 * functions are summarized as follow:
306 * hash_function Y X N p
307 * ------------- --- --- --- -------
309 * hash_words 3 32 12 0.68
310 * jhash_words 3 32 12 0.68
311 * hash_bytes128 16 128 23 0.22
314 check_3word_hash(hash_words, "hash_words");
315 check_3word_hash(jhash_words, "jhash_words");
316 check_256byte_hash(hash_bytes128, "hash_bytes128", 23);
319 OVSTEST_REGISTER("test-hash", test_hash_main);