--- /dev/null
+/*
+ * Copyright (c) 2015 Cisco and/or its affiliates.
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at:
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+/*
+ Copyright (c) 2005 Eliot Dresselhaus
+
+ Permission is hereby granted, free of charge, to any person obtaining
+ a copy of this software and associated documentation files (the
+ "Software"), to deal in the Software without restriction, including
+ without limitation the rights to use, copy, modify, merge, publish,
+ distribute, sublicense, and/or sell copies of the Software, and to
+ permit persons to whom the Software is furnished to do so, subject to
+ the following conditions:
+
+ The above copyright notice and this permission notice shall be
+ included in all copies or substantial portions of the Software.
+
+ THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+ LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+ OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+*/
+
+/* This is all stolen from Bob Jenkins and reworked for clib. Thanks
+ once again Bob for the great work. */
+
+/*
+------------------------------------------------------------------------------
+perfect.c: code to generate code for a hash for perfect hashing.
+(c) Bob Jenkins, September 1996, December 1999
+You may use this code in any way you wish, and it is free. No warranty.
+I hereby place this in the public domain.
+Source is http://burtleburtle.net/bob/c/perfect.c
+
+This generates a minimal perfect hash function. That means, given a
+set of n keys, this determines a hash function that maps each of
+those keys into a value in 0..n-1 with no collisions.
+
+The perfect hash function first uses a normal hash function on the key
+to determine (a,b) such that the pair (a,b) is distinct for all
+keys, then it computes a^scramble[tab[b]] to get the final perfect hash.
+tab[] is an array of 1-byte values and scramble[] is a 256-term array of
+2-byte or 4-byte values. If there are n keys, the length of tab[] is a
+power of two between n/3 and n.
+
+I found the idea of computing distinct (a,b) values in "Practical minimal
+perfect hash functions for large databases", Fox, Heath, Chen, and Daoud,
+Communications of the ACM, January 1992. They found the idea in Chichelli
+(CACM Jan 1980). Beyond that, our methods differ.
+
+The key is hashed to a pair (a,b) where a in 0..*alen*-1 and b in
+0..*blen*-1. A fast hash function determines both a and b
+simultaneously. Any decent hash function is likely to produce
+hashes so that (a,b) is distinct for all pairs. I try the hash
+using different values of *salt* until all pairs are distinct.
+
+The final hash is (a XOR scramble[tab[b]]). *scramble* is a
+predetermined mapping of 0..255 into 0..smax-1. *tab* is an
+array that we fill in in such a way as to make the hash perfect.
+
+First we fill in all values of *tab* that are used by more than one
+key. We try all possible values for each position until one works.
+
+This leaves m unmapped keys and m values that something could hash to.
+If you treat unmapped keys as lefthand nodes and unused hash values
+as righthand nodes, and draw a line connecting each key to each hash
+value it could map to, you get a bipartite graph. We attempt to
+find a perfect matching in this graph. If we succeed, we have
+determined a perfect hash for the whole set of keys.
+
+*scramble* is used because (a^tab[i]) clusters keys around *a*.
+------------------------------------------------------------------------------
+*/
+
+#include <vppinfra/bitmap.h>
+#include <vppinfra/format.h>
+#include <vppinfra/phash.h>
+#include <vppinfra/random.h>
+
+static void
+init_keys_direct_u32 (phash_main_t * pm)
+{
+ int n_keys_left, b_mask, a_shift;
+ u32 seed;
+ phash_key_t *k;
+
+ seed = pm->hash_seed;
+ b_mask = (1 << pm->b_bits) - 1;
+ a_shift = BITS (seed) - pm->a_bits;
+
+ k = pm->keys;
+ n_keys_left = vec_len (pm->keys);
+
+ while (n_keys_left >= 2)
+ {
+ u32 x0, y0, z0;
+ u32 x1, y1, z1;
+
+ x0 = y0 = z0 = seed;
+ x1 = y1 = z1 = seed;
+ x0 += (u32) k[0].key;
+ x1 += (u32) k[1].key;
+
+ hash_mix32 (x0, y0, z0);
+ hash_mix32 (x1, y1, z1);
+
+ k[0].b = z0 & b_mask;
+ k[1].b = z1 & b_mask;
+ k[0].a = z0 >> a_shift;
+ k[1].a = z1 >> a_shift;
+ if (PREDICT_FALSE (a_shift >= BITS (z0)))
+ k[0].a = k[1].a = 0;
+
+ k += 2;
+ n_keys_left -= 2;
+ }
+
+ if (n_keys_left >= 1)
+ {
+ u32 x0, y0, z0;
+
+ x0 = y0 = z0 = seed;
+ x0 += k[0].key;
+
+ hash_mix32 (x0, y0, z0);
+
+ k[0].b = z0 & b_mask;
+ k[0].a = z0 >> a_shift;
+ if (PREDICT_FALSE (a_shift >= BITS (z0)))
+ k[0].a = 0;
+
+ k += 1;
+ n_keys_left -= 1;
+ }
+}
+
+static void
+init_keys_direct_u64 (phash_main_t * pm)
+{
+ int n_keys_left, b_mask, a_shift;
+ u64 seed;
+ phash_key_t *k;
+
+ seed = pm->hash_seed;
+ b_mask = (1 << pm->b_bits) - 1;
+ a_shift = BITS (seed) - pm->a_bits;
+
+ k = pm->keys;
+ n_keys_left = vec_len (pm->keys);
+
+ while (n_keys_left >= 2)
+ {
+ u64 x0, y0, z0;
+ u64 x1, y1, z1;
+
+ x0 = y0 = z0 = seed;
+ x1 = y1 = z1 = seed;
+ x0 += (u64) k[0].key;
+ x1 += (u64) k[1].key;
+
+ hash_mix64 (x0, y0, z0);
+ hash_mix64 (x1, y1, z1);
+
+ k[0].b = z0 & b_mask;
+ k[1].b = z1 & b_mask;
+ k[0].a = z0 >> a_shift;
+ k[1].a = z1 >> a_shift;
+ if (PREDICT_FALSE (a_shift >= BITS (z0)))
+ k[0].a = k[1].a = 0;
+
+ k += 2;
+ n_keys_left -= 2;
+ }
+
+ if (n_keys_left >= 1)
+ {
+ u64 x0, y0, z0;
+
+ x0 = y0 = z0 = seed;
+ x0 += k[0].key;
+
+ hash_mix64 (x0, y0, z0);
+
+ k[0].b = z0 & b_mask;
+ k[0].a = z0 >> a_shift;
+ if (PREDICT_FALSE (a_shift >= BITS (z0)))
+ k[0].a = 0;
+
+ k += 1;
+ n_keys_left -= 1;
+ }
+}
+
+static void
+init_keys_indirect_u32 (phash_main_t * pm)
+{
+ int n_keys_left, b_mask, a_shift;
+ u32 seed;
+ phash_key_t *k;
+
+ seed = pm->hash_seed;
+ b_mask = (1 << pm->b_bits) - 1;
+ a_shift = BITS (seed) - pm->a_bits;
+
+ k = pm->keys;
+ n_keys_left = vec_len (pm->keys);
+
+ while (n_keys_left >= 2)
+ {
+ u32 xyz[6];
+ u32 x0, y0, z0;
+ u32 x1, y1, z1;
+
+ pm->key_seed2 (pm->private, k[0].key, k[1].key, &xyz);
+
+ x0 = y0 = z0 = seed;
+ x1 = y1 = z1 = seed;
+ x0 += xyz[0];
+ y0 += xyz[1];
+ z0 += xyz[2];
+ x1 += xyz[3];
+ y1 += xyz[4];
+ z1 += xyz[5];
+
+ hash_mix32 (x0, y0, z0);
+ hash_mix32 (x1, y1, z1);
+
+ k[0].b = z0 & b_mask;
+ k[1].b = z1 & b_mask;
+ k[0].a = z0 >> a_shift;
+ k[1].a = z1 >> a_shift;
+ if (PREDICT_FALSE (a_shift >= BITS (z0)))
+ k[0].a = k[1].a = 0;
+
+ k += 2;
+ n_keys_left -= 2;
+ }
+
+ if (n_keys_left >= 1)
+ {
+ u32 xyz[3];
+ u32 x0, y0, z0;
+
+ pm->key_seed1 (pm->private, k[0].key, &xyz);
+
+ x0 = y0 = z0 = seed;
+ x0 += xyz[0];
+ y0 += xyz[1];
+ z0 += xyz[2];
+
+ hash_mix32 (x0, y0, z0);
+
+ k[0].b = z0 & b_mask;
+ k[0].a = z0 >> a_shift;
+ if (PREDICT_FALSE (a_shift >= BITS (z0)))
+ k[0].a = 0;
+
+ k += 1;
+ n_keys_left -= 1;
+ }
+}
+
+static void
+init_keys_indirect_u64 (phash_main_t * pm)
+{
+ int n_keys_left, b_mask, a_shift;
+ u64 seed;
+ phash_key_t *k;
+
+ seed = pm->hash_seed;
+ b_mask = (1 << pm->b_bits) - 1;
+ a_shift = BITS (seed) - pm->a_bits;
+
+ k = pm->keys;
+ n_keys_left = vec_len (pm->keys);
+
+ while (n_keys_left >= 2)
+ {
+ u64 xyz[6];
+ u64 x0, y0, z0;
+ u64 x1, y1, z1;
+
+ pm->key_seed2 (pm->private, k[0].key, k[1].key, &xyz);
+
+ x0 = y0 = z0 = seed;
+ x1 = y1 = z1 = seed;
+ x0 += xyz[0];
+ y0 += xyz[1];
+ z0 += xyz[2];
+ x1 += xyz[3];
+ y1 += xyz[4];
+ z1 += xyz[5];
+
+ hash_mix64 (x0, y0, z0);
+ hash_mix64 (x1, y1, z1);
+
+ k[0].b = z0 & b_mask;
+ k[1].b = z1 & b_mask;
+ k[0].a = z0 >> a_shift;
+ k[1].a = z1 >> a_shift;
+ if (PREDICT_FALSE (a_shift >= BITS (z0)))
+ k[0].a = k[1].a = 0;
+
+ k += 2;
+ n_keys_left -= 2;
+ }
+
+ if (n_keys_left >= 1)
+ {
+ u64 xyz[3];
+ u64 x0, y0, z0;
+
+ pm->key_seed1 (pm->private, k[0].key, &xyz);
+
+ x0 = y0 = z0 = seed;
+ x0 += xyz[0];
+ y0 += xyz[1];
+ z0 += xyz[2];
+
+ hash_mix64 (x0, y0, z0);
+
+ k[0].b = z0 & b_mask;
+ k[0].a = z0 >> a_shift;
+ if (PREDICT_FALSE (a_shift >= BITS (z0)))
+ k[0].a = 0;
+
+ k += 1;
+ n_keys_left -= 1;
+ }
+}
+
+/*
+ * insert keys into table according to key->b
+ * check if the initial hash might work
+ */
+static int
+init_tabb (phash_main_t * pm)
+{
+ int no_collisions;
+ phash_tabb_t *tb;
+ phash_key_t *k, *l;
+
+ if (pm->key_seed1)
+ {
+ if (pm->flags & PHASH_FLAG_MIX64)
+ init_keys_indirect_u64 (pm);
+ else
+ init_keys_indirect_u32 (pm);
+ }
+ else
+ {
+ if (pm->flags & PHASH_FLAG_MIX64)
+ init_keys_direct_u64 (pm);
+ else
+ init_keys_direct_u32 (pm);
+ }
+
+ if (!pm->tabb)
+ vec_resize (pm->tabb, 1 << pm->b_bits);
+ else
+ vec_foreach (tb, pm->tabb) phash_tabb_free (tb);
+
+ /* Two keys with the same (a,b) guarantees a collision */
+ no_collisions = 1;
+ vec_foreach (k, pm->keys)
+ {
+ u32 i, *ki;
+
+ tb = pm->tabb + k->b;
+ ki = tb->keys;
+ for (i = 0; i < vec_len (ki); i++)
+ {
+ l = pm->keys + ki[i];
+ if (k->a == l->a)
+ {
+ /* Given keys are supposed to be unique. */
+ if (pm->key_is_equal
+ && pm->key_is_equal (pm->private, l->key, k->key))
+ clib_error ("duplicate keys");
+ no_collisions = 0;
+ goto done;
+ }
+ }
+
+ vec_add1 (tb->keys, k - pm->keys);
+ }
+
+done:
+ return no_collisions;
+}
+
+/* Try to apply an augmenting list */
+static int
+apply (phash_main_t * pm, u32 tail, u32 rollback)
+{
+ phash_key_t *k;
+ phash_tabb_t *pb;
+ phash_tabq_t *q_child, *q_parent;
+ u32 ki, i, hash, child, parent;
+ u32 stabb; /* scramble[tab[b]] */
+ int no_collision;
+
+ no_collision = 1;
+
+ /* Walk from child to parent until root is reached. */
+ for (child = tail - 1; child; child = parent)
+ {
+ q_child = &pm->tabq[child];
+ parent = q_child->parent_q;
+ q_parent = &pm->tabq[parent];
+
+ /* find parent's list of siblings */
+ ASSERT (q_parent->b_q < vec_len (pm->tabb));
+ pb = pm->tabb + q_parent->b_q;
+
+ /* erase old hash values */
+ stabb = pm->scramble[pb->val_b];
+ for (i = 0; i < vec_len (pb->keys); i++)
+ {
+ ki = pb->keys[i];
+ k = pm->keys + ki;
+ hash = k->a ^ stabb;
+
+ /* Erase hash for all of child's siblings. */
+ if (ki == pm->tabh[hash])
+ pm->tabh[hash] = ~0;
+ }
+
+ /* change pb->val_b, which will change the hashes of all parent siblings */
+ pb->val_b = rollback ? q_child->oldval_q : q_child->newval_q;
+
+ /* set new hash values */
+ stabb = pm->scramble[pb->val_b];
+ for (i = 0; i < vec_len (pb->keys); i++)
+ {
+ ki = pb->keys[i];
+ k = pm->keys + ki;
+
+ hash = k->a ^ stabb;
+ if (rollback)
+ {
+ if (parent == 0)
+ continue; /* root never had a hash */
+ }
+ else if (pm->tabh[hash] != ~0)
+ {
+ /* Very rare case: roll back any changes. */
+ apply (pm, tail, /* rollback changes */ 1);
+ no_collision = 0;
+ goto done;
+ }
+ pm->tabh[hash] = ki;
+ }
+ }
+
+done:
+ return no_collision;
+}
+
+
+/*
+-------------------------------------------------------------------------------
+augment(): Add item to the mapping.
+
+Construct a spanning tree of *b*s with *item* as root, where each
+parent can have all its hashes changed (by some new val_b) with
+at most one collision, and each child is the b of that collision.
+
+I got this from Tarjan's "Data Structures and Network Algorithms". The
+path from *item* to a *b* that can be remapped with no collision is
+an "augmenting path". Change values of tab[b] along the path so that
+the unmapped key gets mapped and the unused hash value gets used.
+
+Assuming 1 key per b, if m out of n hash values are still unused,
+you should expect the transitive closure to cover n/m nodes before
+an unused node is found. Sum(i=1..n)(n/i) is about nlogn, so expect
+this approach to take about nlogn time to map all single-key b's.
+-------------------------------------------------------------------------------
+
+high_water: a value higher than any now in tabb[].water_b.
+*/
+static int
+augment (phash_main_t * pm, u32 b_root, u32 high_water)
+{
+ u32 q; /* current position walking through the queue */
+ u32 tail; /* tail of the queue. 0 is the head of the queue. */
+ phash_tabb_t *tb_parent, *tb_child, *tb_hit;
+ phash_key_t *k_parent, *k_child;
+ u32 v, v_limit; /* possible value for myb->val_b */
+ u32 i, ki, hash;
+
+ v_limit =
+ 1 << ((pm->flags & PHASH_FLAG_USE_SCRAMBLE) ? pm->s_bits : BITS (u8));
+
+ /* Initialize the root of the spanning tree. */
+ pm->tabq[0].b_q = b_root;
+ tail = 1;
+
+ /* construct the spanning tree by walking the queue, add children to tail */
+ for (q = 0; q < tail; q++)
+ {
+ if ((pm->flags & PHASH_FLAG_FAST_MODE)
+ && !(pm->flags & PHASH_FLAG_MINIMAL) && q == 1)
+ break; /* don't do transitive closure */
+
+ tb_parent = pm->tabb + pm->tabq[q].b_q; /* the b for this node */
+
+ for (v = 0; v < v_limit; v++)
+ {
+ tb_child = 0;
+
+ for (i = 0; i < vec_len (tb_parent->keys); i++)
+ {
+ ki = tb_parent->keys[i];
+ k_parent = pm->keys + ki;
+
+ hash = k_parent->a ^ pm->scramble[v];
+ if (hash >= pm->hash_max)
+ goto try_next_v; /* hash code out of bounds => we can't use this v */
+
+ ki = pm->tabh[hash];
+ if (ki == ~0)
+ continue;
+
+ k_child = pm->keys + ki;
+ tb_hit = pm->tabb + k_child->b;
+
+ if (tb_child)
+ {
+ /* Hit at most one child b. */
+ if (tb_child == tb_hit)
+ goto try_next_v;
+ }
+ else
+ {
+ /* Remember this as child b. */
+ tb_child = tb_hit;
+ if (tb_hit->water_b == high_water)
+ goto try_next_v; /* already explored */
+ }
+ }
+
+ /* tb_parent with v has either one or zero collisions. */
+
+ /* add childb to the queue of reachable things */
+ if (tb_child)
+ tb_child->water_b = high_water;
+ pm->tabq[tail].b_q = tb_child ? tb_child - pm->tabb : ~0;
+ pm->tabq[tail].newval_q = v; /* how to make parent (myb) use this hash */
+ pm->tabq[tail].oldval_q = tb_parent->val_b; /* need this for rollback */
+ pm->tabq[tail].parent_q = q;
+ ++tail;
+
+ /* Found a v with no collisions? */
+ if (!tb_child)
+ {
+ /* Try to apply the augmenting path. */
+ if (apply (pm, tail, /* rollback */ 0))
+ return 1; /* success, item was added to the perfect hash */
+ --tail; /* don't know how to handle such a child! */
+ }
+
+ try_next_v:
+ ;
+ }
+ }
+ return 0;
+}
+
+
+static phash_tabb_t *sort_tabb;
+
+static int
+phash_tabb_compare (void *a1, void *a2)
+{
+ u32 *b1 = a1;
+ u32 *b2 = a2;
+ phash_tabb_t *tb1, *tb2;
+
+ tb1 = sort_tabb + b1[0];
+ tb2 = sort_tabb + b2[0];
+
+ return ((int) vec_len (tb2->keys) - (int) vec_len (tb1->keys));
+}
+
+/* find a mapping that makes this a perfect hash */
+static int
+perfect (phash_main_t * pm)
+{
+ u32 i;
+
+ /* clear any state from previous attempts */
+ if (vec_bytes (pm->tabh))
+ memset (pm->tabh, ~0, vec_bytes (pm->tabh));
+
+ vec_validate (pm->tabb_sort, vec_len (pm->tabb) - 1);
+ for (i = 0; i < vec_len (pm->tabb_sort); i++)
+ pm->tabb_sort[i] = i;
+
+ sort_tabb = pm->tabb;
+
+ vec_sort_with_function (pm->tabb_sort, phash_tabb_compare);
+
+ /* In descending order by number of keys, map all *b*s */
+ for (i = 0; i < vec_len (pm->tabb_sort); i++)
+ {
+ if (!augment (pm, pm->tabb_sort[i], i + 1))
+ return 0;
+ }
+
+ /* Success! We found a perfect hash of all keys into 0..nkeys-1. */
+ return 1;
+}
+
+
+/*
+ * Find initial a_bits = log2 (a_max), b_bits = log2 (b_max).
+ * Initial a_max and b_max values were found empirically. Some factors:
+ *
+ * If s_max<256 there is no scramble, so tab[b] needs to cover 0..s_max-1.
+ *
+ * a_max and b_max must be powers of 2 because the values in 0..a_max-1 and
+ * 0..b_max-1 are produced by applying a bitmask to the initial hash function.
+ *
+ * a_max must be less than s_max, in fact less than n_keys, because otherwise
+ * there would often be no i such that a^scramble[i] is in 0..n_keys-1 for
+ * all the *a*s associated with a given *b*, so there would be no legal
+ * value to assign to tab[b]. This only matters when we're doing a minimal
+ * perfect hash.
+ *
+ * It takes around 800 trials to find distinct (a,b) with nkey=s_max*(5/8)
+ * and a_max*b_max = s_max*s_max/32.
+ *
+ * Values of b_max less than s_max/4 never work, and s_max/2 always works.
+ *
+ * We want b_max as small as possible because it is the number of bytes in
+ * the huge array we must create for the perfect hash.
+ *
+ * When nkey <= s_max*(5/8), b_max=s_max/4 works much more often with
+ * a_max=s_max/8 than with a_max=s_max/4. Above s_max*(5/8), b_max=s_max/4
+ * doesn't seem to care whether a_max=s_max/8 or a_max=s_max/4. I think it
+ * has something to do with 5/8 = 1/8 * 5. For example examine 80000,
+ * 85000, and 90000 keys with different values of a_max. This only matters
+ * if we're doing a minimal perfect hash.
+ *
+ * When a_max*b_max <= 1<<U32BITS, the initial hash must produce one integer.
+ * Bigger than that it must produce two integers, which increases the
+ * cost of the hash per character hashed.
+ */
+static void
+guess_initial_parameters (phash_main_t * pm)
+{
+ u32 s_bits, s_max, a_max, b_max, n_keys;
+ int is_minimal, is_fast_mode;
+ const u32 b_max_use_scramble_threshold = 4096;
+
+ is_minimal = (pm->flags & PHASH_FLAG_MINIMAL) != 0;
+ is_fast_mode = (pm->flags & PHASH_FLAG_FAST_MODE) != 0;
+
+ n_keys = vec_len (pm->keys);
+ s_bits = max_log2 (n_keys);
+ s_max = 1 << s_bits;
+ a_max = 0;
+
+ if (is_minimal)
+ {
+ switch (s_bits)
+ {
+ case 0:
+ a_max = 1;
+ b_max = 1;
+ case 1:
+ case 2:
+ case 3:
+ case 4:
+ case 5:
+ case 6:
+ case 7:
+ case 8:
+ /*
+ * Was: a_max = is_minimal ? s_max / 2 : s_max;
+ * However, we know that is_minimal must be true, so the
+ * if-arm of the ternary expression is always executed.
+ */
+ a_max = s_max / 2;
+ b_max = s_max / 2;
+ break;
+ case 9:
+ case 10:
+ case 11:
+ case 12:
+ case 13:
+ case 14:
+ case 15:
+ case 16:
+ case 17:
+ if (is_fast_mode)
+ {
+ a_max = s_max / 2;
+ b_max = s_max / 4;
+ }
+ else if (s_max / 4 < b_max_use_scramble_threshold)
+ {
+ if (n_keys <= s_max * 0.52)
+ a_max = b_max = s_max / 8;
+ else
+ a_max = b_max = s_max / 4;
+ }
+ else
+ {
+ a_max = ((n_keys <= s_max * (5.0 / 8.0)) ? s_max / 8 :
+ (n_keys <=
+ s_max * (3.0 / 4.0)) ? s_max / 4 : s_max / 2);
+ b_max = s_max / 4; /* always give the small size a shot */
+ }
+ break;
+ case 18:
+ if (is_fast_mode)
+ a_max = b_max = s_max / 2;
+ else
+ {
+ a_max = s_max / 8; /* never require the multiword hash */
+ b_max = (n_keys <= s_max * (5.0 / 8.0)) ? s_max / 4 : s_max / 2;
+ }
+ break;
+ case 19:
+ case 20:
+ a_max = (n_keys <= s_max * (5.0 / 8.0)) ? s_max / 8 : s_max / 2;
+ b_max = (n_keys <= s_max * (5.0 / 8.0)) ? s_max / 4 : s_max / 2;
+ break;
+ default:
+ /* Just find a hash as quick as possible.
+ We'll be thrashing virtual memory at this size. */
+ a_max = b_max = s_max / 2;
+ break;
+ }
+ }
+ else
+ {
+ /* Non-minimal perfect hash. */
+ if (is_fast_mode && n_keys > s_max * 0.8)
+ {
+ s_max *= 2;
+ s_bits += 1;
+ }
+
+ if (s_max / 4 <= (1 << 14))
+ b_max = ((n_keys <= s_max * 0.56) ? s_max / 32 :
+ (n_keys <= s_max * 0.74) ? s_max / 16 : s_max / 8);
+ else
+ b_max = ((n_keys <= s_max * 0.6) ? s_max / 16 :
+ (n_keys <= s_max * 0.8) ? s_max / 8 : s_max / 4);
+
+ if (is_fast_mode && b_max < s_max / 8)
+ b_max = s_max / 8;
+
+ if (a_max < 1)
+ a_max = 1;
+ if (b_max < 1)
+ b_max = 1;
+ }
+
+ ASSERT (s_max == (1 << s_bits));
+ ASSERT (is_pow2 (a_max));
+ ASSERT (is_pow2 (b_max));
+ pm->s_bits = s_bits;
+ pm->a_bits = min_log2 (a_max);
+ pm->b_bits = min_log2 (b_max);
+ if (b_max >= b_max_use_scramble_threshold)
+ pm->flags |= PHASH_FLAG_USE_SCRAMBLE;
+}
+
+/* compute p(x), where p is a permutation of 0..(1<<nbits)-1 */
+/* permute(0)=0. This is intended and useful. */
+always_inline u32
+scramble_permute (u32 x, u32 nbits)
+{
+ int i;
+ int mask = (1 << nbits) - 1;
+ int const2 = 1 + nbits / 2;
+ int const3 = 1 + nbits / 3;
+ int const4 = 1 + nbits / 4;
+ int const5 = 1 + nbits / 5;
+ for (i = 0; i < 20; i++)
+ {
+ x = (x + (x << const2)) & mask;
+ x = (x ^ (x >> const3));
+ x = (x + (x << const4)) & mask;
+ x = (x ^ (x >> const5));
+ }
+ return x;
+}
+
+/* initialize scramble[] with distinct random values in 0..smax-1 */
+static void
+scramble_init (phash_main_t * pm)
+{
+ u32 i;
+
+ /* fill scramble[] with distinct random integers in 0..smax-1 */
+ vec_validate (pm->scramble, (1 << (pm->s_bits < 8 ? 8 : pm->s_bits)) - 1);
+ for (i = 0; i < vec_len (pm->scramble); i++)
+ pm->scramble[i] = scramble_permute (i, pm->s_bits);
+}
+
+/* Try to find a perfect hash function. */
+clib_error_t *
+phash_find_perfect_hash (phash_main_t * pm)
+{
+ clib_error_t *error = 0;
+ u32 max_a_bits, n_tries_this_a_b, want_minimal;
+
+ /* guess initial values for s_max, a_max and b_max */
+ guess_initial_parameters (pm);
+
+ want_minimal = pm->flags & PHASH_FLAG_MINIMAL;
+
+new_s:
+ if (pm->b_bits == 0)
+ pm->a_bits = pm->s_bits;
+
+ max_a_bits = pm->s_bits - want_minimal;
+ if (max_a_bits < 1)
+ max_a_bits = 1;
+
+ pm->hash_max = want_minimal ? vec_len (pm->keys) : (1 << pm->s_bits);
+
+ scramble_init (pm);
+
+ /* Allocate working memory. */
+ vec_free (pm->tabh);
+ vec_validate_init_empty (pm->tabh, pm->hash_max - 1, ~0);
+ vec_free (pm->tabq);
+ vec_validate (pm->tabq, 1 << pm->b_bits);
+
+ /* Actually find the perfect hash */
+ n_tries_this_a_b = 0;
+ while (1)
+ {
+ /* Choose random hash seeds until keys become unique. */
+ pm->hash_seed = random_u64 (&pm->random_seed);
+ pm->n_seed_trials++;
+ if (init_tabb (pm))
+ {
+ /* Found unique (A, B). */
+
+ /* Hash may already be perfect. */
+ if (pm->b_bits == 0)
+ goto done;
+
+ pm->n_perfect_calls++;
+ if (perfect (pm))
+ goto done;
+
+ goto increase_b;
+ }
+
+ /* Keep trying with different seed value. */
+ n_tries_this_a_b++;
+ if (n_tries_this_a_b < 2048)
+ continue;
+
+ /* Try to put more bits in (A,B) to make distinct (A,B) more likely */
+ if (pm->a_bits < max_a_bits)
+ pm->a_bits++;
+ else if (pm->b_bits < pm->s_bits)
+ {
+ increase_b:
+ vec_resize (pm->tabb, vec_len (pm->tabb));
+ vec_resize (pm->tabq, vec_len (pm->tabq));
+ pm->b_bits++;
+ }
+ else
+ {
+ /* Can't increase (A, B) any more, so try increasing S. */
+ goto new_s;
+ }
+ }
+
+done:
+ /* Construct mapping table for hash lookups. */
+ if (!error)
+ {
+ u32 b, v;
+
+ pm->a_shift = ((pm->flags & PHASH_FLAG_MIX64) ? 64 : 32) - pm->a_bits;
+ pm->b_mask = (1 << pm->b_bits) - 1;
+
+ vec_resize (pm->tab, vec_len (pm->tabb));
+ for (b = 0; b < vec_len (pm->tabb); b++)
+ {
+ v = pm->tabb[b].val_b;
+
+ /* Apply scramble now for small enough value of b_bits. */
+ if (!(pm->flags & PHASH_FLAG_USE_SCRAMBLE))
+ v = pm->scramble[v];
+
+ pm->tab[b] = v;
+ }
+ }
+
+ /* Free working memory. */
+ phash_main_free_working_memory (pm);
+
+ return error;
+}
+
+/* Slow hash computation for general keys. */
+uword
+phash_hash_slow (phash_main_t * pm, uword key)
+{
+ u32 a, b, v;
+
+ if (pm->flags & PHASH_FLAG_MIX64)
+ {
+ u64 x0, y0, z0;
+
+ x0 = y0 = z0 = pm->hash_seed;
+
+ if (pm->key_seed1)
+ {
+ u64 xyz[3];
+ pm->key_seed1 (pm->private, key, &xyz);
+ x0 += xyz[0];
+ y0 += xyz[1];
+ z0 += xyz[2];
+ }
+ else
+ x0 += key;
+
+ hash_mix64 (x0, y0, z0);
+
+ a = z0 >> pm->a_shift;
+ b = z0 & pm->b_mask;
+ }
+ else
+ {
+ u32 x0, y0, z0;
+
+ x0 = y0 = z0 = pm->hash_seed;
+
+ if (pm->key_seed1)
+ {
+ u32 xyz[3];
+ pm->key_seed1 (pm->private, key, &xyz);
+ x0 += xyz[0];
+ y0 += xyz[1];
+ z0 += xyz[2];
+ }
+ else
+ x0 += key;
+
+ hash_mix32 (x0, y0, z0);
+
+ a = z0 >> pm->a_shift;
+ b = z0 & pm->b_mask;
+ }
+
+ v = pm->tab[b];
+ if (pm->flags & PHASH_FLAG_USE_SCRAMBLE)
+ v = pm->scramble[v];
+ return a ^ v;
+}
+
+/* Verify that perfect hash is perfect. */
+clib_error_t *
+phash_validate (phash_main_t * pm)
+{
+ phash_key_t *k;
+ uword *unique_bitmap = 0;
+ clib_error_t *error = 0;
+
+ vec_foreach (k, pm->keys)
+ {
+ uword h = phash_hash_slow (pm, k->key);
+
+ if (h >= pm->hash_max)
+ {
+ error = clib_error_return (0, "hash out of range %wd", h);
+ goto done;
+ }
+
+ if (clib_bitmap_get (unique_bitmap, h))
+ {
+ error = clib_error_return (0, "hash non-unique");
+ goto done;
+ }
+
+ unique_bitmap = clib_bitmap_ori (unique_bitmap, h);
+ }
+
+done:
+ clib_bitmap_free (unique_bitmap);
+ return error;
+}
+
+/*
+ * fd.io coding-style-patch-verification: ON
+ *
+ * Local Variables:
+ * eval: (c-set-style "gnu")
+ * End:
+ */
Code Review / vpp.git / blobdiff