c0e157e3b2
One must build yasm (included in the yasm directory) before building GMP, if building on an x86_64 machine. Note: make test and make tune do not currently build.
1190 lines
41 KiB
C
1190 lines
41 KiB
C
/* Modified for use with yasm by Peter Johnson.
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* $Id: perfect.c 1942 2007-09-11 02:11:19Z peter $
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*/
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/*
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------------------------------------------------------------------------------
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perfect.c: code to generate code for a hash for perfect hashing.
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(c) Bob Jenkins, September 1996, December 1999
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You may use this code in any way you wish, and it is free. No warranty.
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I hereby place this in the public domain.
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Source is http://burtleburtle.net/bob/c/perfect.c
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This generates a minimal perfect hash function. That means, given a
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set of n keys, this determines a hash function that maps each of
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those keys into a value in 0..n-1 with no collisions.
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The perfect hash function first uses a normal hash function on the key
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to determine (a,b) such that the pair (a,b) is distinct for all
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keys, then it computes a^scramble[tab[b]] to get the final perfect hash.
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tab[] is an array of 1-byte values and scramble[] is a 256-term array of
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2-byte or 4-byte values. If there are n keys, the length of tab[] is a
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power of two between n/3 and n.
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I found the idea of computing distinct (a,b) values in "Practical minimal
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perfect hash functions for large databases", Fox, Heath, Chen, and Daoud,
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Communications of the ACM, January 1992. They found the idea in Chichelli
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(CACM Jan 1980). Beyond that, our methods differ.
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The key is hashed to a pair (a,b) where a in 0..*alen*-1 and b in
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0..*blen*-1. A fast hash function determines both a and b
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simultaneously. Any decent hash function is likely to produce
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hashes so that (a,b) is distinct for all pairs. I try the hash
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using different values of *salt* until all pairs are distinct.
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The final hash is (a XOR scramble[tab[b]]). *scramble* is a
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predetermined mapping of 0..255 into 0..smax-1. *tab* is an
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array that we fill in in such a way as to make the hash perfect.
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First we fill in all values of *tab* that are used by more than one
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key. We try all possible values for each position until one works.
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This leaves m unmapped keys and m values that something could hash to.
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If you treat unmapped keys as lefthand nodes and unused hash values
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as righthand nodes, and draw a line connecting each key to each hash
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value it could map to, you get a bipartite graph. We attempt to
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find a perfect matching in this graph. If we succeed, we have
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determined a perfect hash for the whole set of keys.
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*scramble* is used because (a^tab[i]) clusters keys around *a*.
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------------------------------------------------------------------------------
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*/
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#include <string.h>
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#include "tools/genperf/standard.h"
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#include "libyasm/coretype.h"
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#include "libyasm/phash.h"
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#include "tools/genperf/perfect.h"
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#define CHECKSTATE 8
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/*
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------------------------------------------------------------------------------
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Find the mapping that will produce a perfect hash
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------------------------------------------------------------------------------
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*/
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/* return the ceiling of the log (base 2) of val */
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ub4 phash_log2(val)
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ub4 val;
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{
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ub4 i;
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for (i=0; ((ub4)1<<i) < val; ++i)
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;
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return i;
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}
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/* compute p(x), where p is a permutation of 0..(1<<nbits)-1 */
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/* permute(0)=0. This is intended and useful. */
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static ub4 permute(
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ub4 x, /* input, a value in some range */
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ub4 nbits) /* input, number of bits in range */
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{
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int i;
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int mask = ((ub4)1<<nbits)-1; /* all ones */
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int const2 = 1+nbits/2;
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int const3 = 1+nbits/3;
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int const4 = 1+nbits/4;
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int const5 = 1+nbits/5;
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for (i=0; i<20; ++i)
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{
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x = (x+(x<<const2)) & mask;
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x = (x^(x>>const3));
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x = (x+(x<<const4)) & mask;
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x = (x^(x>>const5));
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}
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return x;
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}
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/* initialize scramble[] with distinct random values in 0..smax-1 */
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static void scrambleinit(
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ub4 *scramble, /* hash is a^scramble[tab[b]] */
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ub4 smax) /* scramble values should be in 0..smax-1 */
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{
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ub4 i;
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/* fill scramble[] with distinct random integers in 0..smax-1 */
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for (i=0; i<SCRAMBLE_LEN; ++i)
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{
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scramble[i] = permute(i, phash_log2(smax));
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}
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}
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/*
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* Check if key1 and key2 are the same.
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* We already checked (a,b) are the same.
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*/
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static void checkdup(
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key *key1,
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key *key2,
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hashform *form)
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{
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switch(form->hashtype)
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{
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case STRING_HT:
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if ((key1->len_k == key2->len_k) &&
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!memcmp(key1->name_k, key2->name_k, (size_t)key1->len_k))
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{
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fprintf(stderr, "perfect.c: Duplicates keys! %.*s\n",
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(int)key1->len_k, key1->name_k);
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exit(EXIT_FAILURE);
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}
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break;
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case INT_HT:
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if (key1->hash_k == key2->hash_k)
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{
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fprintf(stderr, "perfect.c: Duplicate keys! %.8lx\n", key1->hash_k);
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exit(EXIT_FAILURE);
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}
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break;
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case AB_HT:
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fprintf(stderr, "perfect.c: Duplicate keys! %.8lx %.8lx\n",
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key1->a_k, key1->b_k);
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exit(EXIT_FAILURE);
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break;
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default:
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fprintf(stderr, "perfect.c: Illegal hash type %ld\n", (ub4)form->hashtype);
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exit(EXIT_FAILURE);
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break;
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}
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}
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/*
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* put keys in tabb according to key->b_k
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* check if the initial hash might work
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*/
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static int inittab(
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bstuff *tabb, /* output, list of keys with b for (a,b) */
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ub4 blen, /* length of tabb */
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key *keys, /* list of keys already hashed */
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hashform *form, /* user directives */
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int complete) /* TRUE means to complete init despite collisions */
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{
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int nocollision = TRUE;
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key *mykey;
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memset((void *)tabb, 0, (size_t)(sizeof(bstuff)*blen));
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/* Two keys with the same (a,b) guarantees a collision */
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for (mykey=keys; mykey; mykey=mykey->next_k)
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{
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key *otherkey;
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for (otherkey=tabb[mykey->b_k].list_b;
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otherkey;
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otherkey=otherkey->nextb_k)
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{
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if (mykey->a_k == otherkey->a_k)
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{
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nocollision = FALSE;
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checkdup(mykey, otherkey, form);
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if (!complete)
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return FALSE;
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}
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}
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++tabb[mykey->b_k].listlen_b;
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mykey->nextb_k = tabb[mykey->b_k].list_b;
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tabb[mykey->b_k].list_b = mykey;
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}
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/* no two keys have the same (a,b) pair */
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return nocollision;
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}
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/* Do the initial hash for normal mode (use lookup and checksum) */
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static void initnorm(
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key *keys, /* list of all keys */
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ub4 alen, /* (a,b) has a in 0..alen-1, a power of 2 */
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ub4 blen, /* (a,b) has b in 0..blen-1, a power of 2 */
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ub4 smax, /* maximum range of computable hash values */
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ub4 salt, /* used to initialize the hash function */
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gencode *final) /* output, code for the final hash */
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{
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key *mykey;
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if (phash_log2(alen)+phash_log2(blen) > UB4BITS)
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{
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ub4 initlev = (salt*0x9e3779b9)&0xffffffff; /* the golden ratio; an arbitrary value */
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for (mykey=keys; mykey; mykey=mykey->next_k)
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{
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ub4 i, state[CHECKSTATE];
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for (i=0; i<CHECKSTATE; ++i) state[i] = initlev;
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phash_checksum( mykey->name_k, mykey->len_k, state);
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mykey->a_k = state[0]&(alen-1);
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mykey->b_k = state[1]&(blen-1);
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}
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final->used = 4;
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sprintf(final->line[0],
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" unsigned long i,state[CHECKSTATE],rsl;\n");
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sprintf(final->line[1],
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" for (i=0; i<CHECKSTATE; ++i) state[i]=0x%lx;\n",initlev);
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sprintf(final->line[2],
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" phash_checksum(key, len, state);\n");
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sprintf(final->line[3],
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" rsl = ((state[0]&0x%lx)^scramble[tab[state[1]&0x%lx]]);\n",
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alen-1, blen-1);
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}
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else
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{
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ub4 loga = phash_log2(alen); /* log based 2 of blen */
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ub4 initlev = (salt*0x9e3779b9)&0xffffffff; /* the golden ratio; an arbitrary value */
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for (mykey=keys; mykey; mykey=mykey->next_k)
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{
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ub4 hash = phash_lookup(mykey->name_k, mykey->len_k, initlev);
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mykey->a_k = (loga > 0) ? hash>>(UB4BITS-loga) : 0;
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mykey->b_k = (blen > 1) ? hash&(blen-1) : 0;
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}
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final->used = 2;
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sprintf(final->line[0],
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" unsigned long rsl, val = phash_lookup(key, len, 0x%lxUL);\n", initlev);
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if (smax <= 1)
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{
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sprintf(final->line[1], " rsl = 0;\n");
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}
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else if (blen < USE_SCRAMBLE)
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{
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sprintf(final->line[1], " rsl = ((val>>%ld)^tab[val&0x%lx]);\n",
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UB4BITS-phash_log2(alen), blen-1);
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}
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else
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{
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sprintf(final->line[1], " rsl = ((val>>%ld)^scramble[tab[val&0x%lx]]);\n",
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UB4BITS-phash_log2(alen), blen-1);
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}
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}
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}
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/* Do initial hash for inline mode */
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static void initinl(
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key *keys, /* list of all keys */
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ub4 alen, /* (a,b) has a in 0..alen-1, a power of 2 */
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ub4 blen, /* (a,b) has b in 0..blen-1, a power of 2 */
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ub4 smax, /* range of computable hash values */
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ub4 salt, /* used to initialize the hash function */
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gencode *final) /* generated code for final hash */
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{
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key *mykey;
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ub4 amask = alen-1;
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ub4 blog = phash_log2(blen);
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ub4 initval = salt*0x9e3779b9; /* the golden ratio; an arbitrary value */
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/* It's more important to have b uniform than a, so b is the low bits */
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for (mykey = keys; mykey != (key *)0; mykey = mykey->next_k)
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{
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ub4 hash = initval;
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ub4 i;
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for (i=0; i<mykey->len_k; ++i)
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{
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hash = ((ub1)mykey->name_k[i] ^ hash) + ((hash<<(UB4BITS-6))+(hash>>6));
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}
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mykey->hash_k = hash;
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mykey->a_k = (alen > 1) ? (hash & amask) : 0;
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mykey->b_k = (blen > 1) ? (hash >> (UB4BITS-blog)) : 0;
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}
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final->used = 1;
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if (smax <= 1)
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{
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sprintf(final->line[0], " unsigned long rsl = 0;\n");
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}
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else if (blen < USE_SCRAMBLE)
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{
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sprintf(final->line[0], " unsigned long rsl = ((val & 0x%lx) ^ tab[val >> %ld]);\n",
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amask, UB4BITS-blog);
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}
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else
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{
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sprintf(final->line[0], " unsigned long rsl = ((val & 0x%lx) ^ scramble[tab[val >> %ld]]);\n",
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amask, UB4BITS-blog);
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}
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}
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/*
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* Run a hash function on the key to get a and b
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* Returns:
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* 0: didn't find distinct (a,b) for all keys
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* 1: found distinct (a,b) for all keys, put keys in tabb[]
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* 2: found a perfect hash, no need to do any more work
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*/
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static ub4 initkey(
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key *keys, /* list of all keys */
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ub4 nkeys, /* total number of keys */
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bstuff *tabb, /* stuff indexed by b */
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ub4 alen, /* (a,b) has a in 0..alen-1, a power of 2 */
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ub4 blen, /* (a,b) has b in 0..blen-1, a power of 2 */
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ub4 smax, /* range of computable hash values */
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ub4 salt, /* used to initialize the hash function */
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hashform *form, /* user directives */
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gencode *final) /* code for final hash */
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{
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/* Do the initial hash of the keys */
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switch(form->mode)
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{
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case NORMAL_HM:
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initnorm(keys, alen, blen, smax, salt, final);
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break;
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case INLINE_HM:
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initinl(keys, alen, blen, smax, salt, final);
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break;
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#if 0
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case HEX_HM:
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case DECIMAL_HM:
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finished = inithex(keys, nkeys, alen, blen, smax, salt, final, form);
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if (finished) return 2;
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break;
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#endif
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default:
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fprintf(stderr, "fatal error: illegal mode\n");
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exit(1);
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}
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if (nkeys <= 1)
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{
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final->used = 1;
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sprintf(final->line[0], " unsigned long rsl = 0;\n");
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return 2;
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}
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return inittab(tabb, blen, keys, form, FALSE);
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}
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/* Print an error message and exit if there are duplicates */
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static void duplicates(
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bstuff *tabb, /* array of lists of keys with the same b */
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ub4 blen, /* length of tabb, a power of 2 */
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key *keys,
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hashform *form) /* user directives */
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{
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ub4 i;
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key *key1;
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key *key2;
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(void)inittab(tabb, blen, keys, form, TRUE);
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/* for each b, do nested loops through key list looking for duplicates */
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for (i=0; i<blen; ++i)
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for (key1=tabb[i].list_b; key1; key1=key1->nextb_k)
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for (key2=key1->nextb_k; key2; key2=key2->nextb_k)
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checkdup(key1, key2, form);
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}
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/* Try to apply an augmenting list */
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static int apply(
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bstuff *tabb,
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hstuff *tabh,
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qstuff *tabq,
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ub4 blen,
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ub4 *scramble,
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ub4 tail,
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int rollback) /* FALSE applies augmenting path, TRUE rolls back */
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{
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ub4 hash;
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key *mykey;
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bstuff *pb;
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ub4 child;
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ub4 parent;
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ub4 stabb; /* scramble[tab[b]] */
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/* walk from child to parent */
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for (child=tail-1; child; child=parent)
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{
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parent = tabq[child].parent_q; /* find child's parent */
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pb = tabq[parent].b_q; /* find parent's list of siblings */
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/* erase old hash values */
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stabb = scramble[pb->val_b];
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for (mykey=pb->list_b; mykey; mykey=mykey->nextb_k)
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{
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hash = mykey->a_k^stabb;
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if (mykey == tabh[hash].key_h)
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{ /* erase hash for all of child's siblings */
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tabh[hash].key_h = (key *)0;
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}
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}
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/* change pb->val_b, which will change the hashes of all parent siblings */
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pb->val_b = (rollback ? tabq[child].oldval_q : tabq[child].newval_q);
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/* set new hash values */
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stabb = scramble[pb->val_b];
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for (mykey=pb->list_b; mykey; mykey=mykey->nextb_k)
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{
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hash = mykey->a_k^stabb;
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if (rollback)
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{
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if (parent == 0) continue; /* root never had a hash */
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}
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else if (tabh[hash].key_h)
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{
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/* very rare: roll back any changes */
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apply(tabb, tabh, tabq, blen, scramble, tail, TRUE);
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return FALSE; /* failure, collision */
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}
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tabh[hash].key_h = mykey;
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}
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}
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return TRUE;
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}
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/*
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-------------------------------------------------------------------------------
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augment(): Add item to the mapping.
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Construct a spanning tree of *b*s with *item* as root, where each
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parent can have all its hashes changed (by some new val_b) with
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at most one collision, and each child is the b of that collision.
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I got this from Tarjan's "Data Structures and Network Algorithms". The
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path from *item* to a *b* that can be remapped with no collision is
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an "augmenting path". Change values of tab[b] along the path so that
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the unmapped key gets mapped and the unused hash value gets used.
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Assuming 1 key per b, if m out of n hash values are still unused,
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you should expect the transitive closure to cover n/m nodes before
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an unused node is found. Sum(i=1..n)(n/i) is about nlogn, so expect
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this approach to take about nlogn time to map all single-key b's.
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-------------------------------------------------------------------------------
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*/
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static int augment(
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bstuff *tabb, /* stuff indexed by b */
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hstuff *tabh, /* which key is associated with which hash, indexed by hash */
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qstuff *tabq, /* queue of *b* values, this is the spanning tree */
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ub4 blen, /* length of tabb */
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ub4 *scramble, /* final hash is a^scramble[tab[b]] */
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ub4 smax, /* highest value in scramble */
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bstuff *item, /* &tabb[b] for the b to be mapped */
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ub4 nkeys, /* final hash must be in 0..nkeys-1 */
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ub4 highwater, /* a value higher than any now in tabb[].water_b */
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|
hashform *form) /* TRUE if we should do a minimal perfect hash */
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{
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ub4 q; /* current position walking through the queue */
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ub4 tail; /* tail of the queue. 0 is the head of the queue. */
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ub4 limit=((blen < USE_SCRAMBLE) ? smax : UB1MAXVAL+1);
|
|
ub4 highhash = ((form->perfect == MINIMAL_HP) ? nkeys : smax);
|
|
int trans = (form->speed == SLOW_HS || form->perfect == MINIMAL_HP);
|
|
|
|
/* initialize the root of the spanning tree */
|
|
tabq[0].b_q = item;
|
|
tail = 1;
|
|
|
|
/* construct the spanning tree by walking the queue, add children to tail */
|
|
for (q=0; q<tail; ++q)
|
|
{
|
|
bstuff *myb = tabq[q].b_q; /* the b for this node */
|
|
ub4 i; /* possible value for myb->val_b */
|
|
|
|
if (!trans && (q == 1))
|
|
break; /* don't do transitive closure */
|
|
|
|
for (i=0; i<limit; ++i)
|
|
{
|
|
bstuff *childb = (bstuff *)0; /* the b that this i maps to */
|
|
key *mykey; /* for walking through myb's keys */
|
|
|
|
for (mykey = myb->list_b; mykey; mykey=mykey->nextb_k)
|
|
{
|
|
key *childkey;
|
|
ub4 hash = mykey->a_k^scramble[i];
|
|
|
|
if (hash >= highhash) break; /* out of bounds */
|
|
childkey = tabh[hash].key_h;
|
|
|
|
if (childkey)
|
|
{
|
|
bstuff *hitb = &tabb[childkey->b_k];
|
|
|
|
if (childb)
|
|
{
|
|
if (childb != hitb) break; /* hit at most one child b */
|
|
}
|
|
else
|
|
{
|
|
childb = hitb; /* remember this as childb */
|
|
if (childb->water_b == highwater) break; /* already explored */
|
|
}
|
|
}
|
|
}
|
|
if (mykey) continue; /* myb with i has multiple collisions */
|
|
|
|
/* add childb to the queue of reachable things */
|
|
if (childb) childb->water_b = highwater;
|
|
tabq[tail].b_q = childb;
|
|
tabq[tail].newval_q = (ub2)i; /* how to make parent (myb) use this hash */
|
|
tabq[tail].oldval_q = myb->val_b; /* need this for rollback */
|
|
tabq[tail].parent_q = q;
|
|
++tail;
|
|
|
|
if (!childb)
|
|
{ /* found an *i* with no collisions? */
|
|
/* try to apply the augmenting path */
|
|
if (apply(tabb, tabh, tabq, blen, scramble, tail, FALSE))
|
|
return TRUE; /* success, item was added to the perfect hash */
|
|
|
|
--tail; /* don't know how to handle such a child! */
|
|
}
|
|
}
|
|
}
|
|
return FALSE;
|
|
}
|
|
|
|
|
|
/* find a mapping that makes this a perfect hash */
|
|
static int perfect(
|
|
bstuff *tabb,
|
|
hstuff *tabh,
|
|
qstuff *tabq,
|
|
ub4 blen,
|
|
ub4 smax,
|
|
ub4 *scramble,
|
|
ub4 nkeys,
|
|
hashform *form)
|
|
{
|
|
ub4 maxkeys; /* maximum number of keys for any b */
|
|
ub4 i, j;
|
|
|
|
/* clear any state from previous attempts */
|
|
memset((void *)tabh, 0,
|
|
(size_t)(sizeof(hstuff)*
|
|
((form->perfect == MINIMAL_HP) ? nkeys : smax)));
|
|
memset((void *)tabq, 0, (size_t)(sizeof(qstuff)*(blen+1)));
|
|
|
|
for (maxkeys=0,i=0; i<blen; ++i)
|
|
if (tabb[i].listlen_b > maxkeys)
|
|
maxkeys = tabb[i].listlen_b;
|
|
|
|
/* In descending order by number of keys, map all *b*s */
|
|
for (j=maxkeys; j>0; --j)
|
|
for (i=0; i<blen; ++i)
|
|
if (tabb[i].listlen_b == j)
|
|
if (!augment(tabb, tabh, tabq, blen, scramble, smax, &tabb[i], nkeys,
|
|
i+1, form))
|
|
{
|
|
fprintf(stderr, "fail to map group of size %ld for tab size %ld\n", j, blen);
|
|
return FALSE;
|
|
}
|
|
|
|
/* Success! We found a perfect hash of all keys into 0..nkeys-1. */
|
|
return TRUE;
|
|
}
|
|
|
|
|
|
/*
|
|
* Simple case: user gave (a,b). No more mixing, no guessing alen or blen.
|
|
* This assumes a,b reside in (key->a_k, key->b_k), and final->form == AB_HK.
|
|
*/
|
|
static void hash_ab(
|
|
bstuff **tabb, /* output, tab[] of the perfect hash, length *blen */
|
|
ub4 *alen, /* output, 0..alen-1 is range for a of (a,b) */
|
|
ub4 *blen, /* output, 0..blen-1 is range for b of (a,b) */
|
|
ub4 *salt, /* output, initializes initial hash */
|
|
gencode *final, /* code for final hash */
|
|
ub4 *scramble, /* input, hash = a^scramble[tab[b]] */
|
|
ub4 *smax, /* input, scramble[i] in 0..smax-1 */
|
|
key *keys, /* input, keys to hash */
|
|
ub4 nkeys, /* input, number of keys being hashed */
|
|
hashform *form) /* user directives */
|
|
{
|
|
hstuff *tabh;
|
|
qstuff *tabq;
|
|
key *mykey;
|
|
ub4 i;
|
|
int used_tab;
|
|
|
|
/* initially make smax the first power of two bigger than nkeys */
|
|
*smax = ((ub4)1<<phash_log2(nkeys));
|
|
scrambleinit(scramble, *smax);
|
|
|
|
/* set *alen and *blen based on max A and B from user */
|
|
*alen = 1;
|
|
*blen = 1;
|
|
for (mykey = keys; mykey != (key *)0; mykey = mykey->next_k)
|
|
{
|
|
while (*alen <= mykey->a_k) *alen *= 2;
|
|
while (*blen <= mykey->b_k) *blen *= 2;
|
|
}
|
|
if (*alen > 2**smax)
|
|
{
|
|
fprintf(stderr,
|
|
"perfect.c: Can't deal with (A,B) having A bigger than twice \n");
|
|
fprintf(stderr,
|
|
" the smallest power of two greater or equal to any legal hash.\n");
|
|
exit(EXIT_FAILURE);
|
|
}
|
|
|
|
/* allocate working memory */
|
|
*tabb = (bstuff *)yasm_xmalloc((size_t)(sizeof(bstuff)*(*blen)));
|
|
tabq = (qstuff *)yasm_xmalloc(sizeof(qstuff)*(*blen+1));
|
|
tabh = (hstuff *)yasm_xmalloc(sizeof(hstuff)*(form->perfect == MINIMAL_HP ?
|
|
nkeys : *smax));
|
|
|
|
/* check that (a,b) are distinct and put them in tabb indexed by b */
|
|
(void)inittab(*tabb, *blen, keys, form, FALSE);
|
|
|
|
/* try with smax */
|
|
if (!perfect(*tabb, tabh, tabq, *blen, *smax, scramble, nkeys, form))
|
|
{
|
|
if (form->perfect == MINIMAL_HP)
|
|
{
|
|
fprintf(stderr, "fatal error: Cannot find perfect hash for user (A,B) pairs\n");
|
|
exit(EXIT_FAILURE);
|
|
}
|
|
else
|
|
{
|
|
/* try with 2*smax */
|
|
free((void *)tabh);
|
|
*smax = *smax * 2;
|
|
scrambleinit(scramble, *smax);
|
|
tabh = (hstuff *)yasm_xmalloc(sizeof(hstuff)*(form->perfect == MINIMAL_HP ?
|
|
nkeys : *smax));
|
|
if (!perfect(*tabb, tabh, tabq, *blen, *smax, scramble, nkeys, form))
|
|
{
|
|
fprintf(stderr, "fatal error: Cannot find perfect hash for user (A,B) pairs\n");
|
|
exit(EXIT_FAILURE);
|
|
}
|
|
}
|
|
}
|
|
|
|
/* check if tab[] was really needed */
|
|
for (i=0; i<*blen; ++i)
|
|
{
|
|
if ((*tabb)[i].val_b != 0) break; /* assumes permute(0) == 0 */
|
|
}
|
|
used_tab = (i < *blen);
|
|
|
|
/* write the code for the perfect hash */
|
|
*salt = 1;
|
|
final->used = 1;
|
|
if (!used_tab)
|
|
{
|
|
sprintf(final->line[0], " unsigned long rsl = a;\n");
|
|
}
|
|
else if (*blen < USE_SCRAMBLE)
|
|
{
|
|
sprintf(final->line[0], " unsigned long rsl = (a ^ tab[b]);\n");
|
|
}
|
|
else
|
|
{
|
|
sprintf(final->line[0], " unsigned long rsl = (a ^ scramble[tab[b]]);\n");
|
|
}
|
|
|
|
printf("success, found a perfect hash\n");
|
|
|
|
free((void *)tabq);
|
|
free((void *)tabh);
|
|
}
|
|
|
|
|
|
/* guess initial values for alen and blen */
|
|
static void initalen(
|
|
ub4 *alen, /* output, initial alen */
|
|
ub4 *blen, /* output, initial blen */
|
|
ub4 *smax,/* input, power of two greater or equal to max hash value */
|
|
ub4 nkeys, /* number of keys being hashed */
|
|
hashform *form) /* user directives */
|
|
{
|
|
/*
|
|
* Find initial *alen, *blen
|
|
* Initial alen and blen values were found empirically. Some factors:
|
|
*
|
|
* If smax<256 there is no scramble, so tab[b] needs to cover 0..smax-1.
|
|
*
|
|
* alen and blen must be powers of 2 because the values in 0..alen-1 and
|
|
* 0..blen-1 are produced by applying a bitmask to the initial hash function.
|
|
*
|
|
* alen must be less than smax, in fact less than nkeys, because otherwise
|
|
* there would often be no i such that a^scramble[i] is in 0..nkeys-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=smax*(5/8)
|
|
* and alen*blen = smax*smax/32.
|
|
*
|
|
* Values of blen less than smax/4 never work, and smax/2 always works.
|
|
*
|
|
* We want blen as small as possible because it is the number of bytes in
|
|
* the huge array we must create for the perfect hash.
|
|
*
|
|
* When nkey <= smax*(5/8), blen=smax/4 works much more often with
|
|
* alen=smax/8 than with alen=smax/4. Above smax*(5/8), blen=smax/4
|
|
* doesn't seem to care whether alen=smax/8 or alen=smax/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 alen. This only matters
|
|
* if we're doing a minimal perfect hash.
|
|
*
|
|
* When alen*blen <= 1<<UB4BITS, 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.
|
|
*/
|
|
if (form->perfect == NORMAL_HP)
|
|
{
|
|
if ((form->speed == FAST_HS) && (nkeys > *smax*0.8))
|
|
{
|
|
*smax = *smax * 2;
|
|
}
|
|
|
|
*alen = ((form->hashtype==INT_HT) && *smax>131072) ?
|
|
((ub4)1<<(UB4BITS-phash_log2(*blen))) : /* distinct keys => distinct (A,B) */
|
|
*smax; /* no reason to restrict alen to smax/2 */
|
|
if ((form->hashtype == INT_HT) && *smax < 32)
|
|
*blen = *smax; /* go for function speed not space */
|
|
else if (*smax/4 <= (1<<14))
|
|
*blen = ((nkeys <= *smax*0.56) ? *smax/32 :
|
|
(nkeys <= *smax*0.74) ? *smax/16 : *smax/8);
|
|
else
|
|
*blen = ((nkeys <= *smax*0.6) ? *smax/16 :
|
|
(nkeys <= *smax*0.8) ? *smax/8 : *smax/4);
|
|
|
|
if ((form->speed == FAST_HS) && (*blen < *smax/8))
|
|
*blen = *smax/8;
|
|
|
|
if (*alen < 1) *alen = 1;
|
|
if (*blen < 1) *blen = 1;
|
|
}
|
|
else
|
|
{
|
|
switch(phash_log2(*smax))
|
|
{
|
|
case 0:
|
|
*alen = 1;
|
|
*blen = 1;
|
|
case 1: case 2: case 3: case 4: case 5: case 6: case 7: case 8:
|
|
*alen = (form->perfect == NORMAL_HP) ? *smax : *smax/2;
|
|
*blen = *smax/2;
|
|
break;
|
|
case 9:
|
|
case 10:
|
|
case 11:
|
|
case 12:
|
|
case 13:
|
|
case 14:
|
|
case 15:
|
|
case 16:
|
|
case 17:
|
|
if (form->speed == FAST_HS)
|
|
{
|
|
*alen = *smax/2;
|
|
*blen = *smax/4;
|
|
}
|
|
else if (*smax/4 < USE_SCRAMBLE)
|
|
{
|
|
*alen = ((nkeys <= *smax*0.52) ? *smax/8 : *smax/4);
|
|
*blen = ((nkeys <= *smax*0.52) ? *smax/8 : *smax/4);
|
|
}
|
|
else
|
|
{
|
|
*alen = ((nkeys <= *smax*(5.0/8.0)) ? *smax/8 :
|
|
(nkeys <= *smax*(3.0/4.0)) ? *smax/4 : *smax/2);
|
|
*blen = *smax/4; /* always give the small size a shot */
|
|
}
|
|
break;
|
|
case 18:
|
|
if (form->speed == FAST_HS)
|
|
{
|
|
*alen = *smax/2;
|
|
*blen = *smax/2;
|
|
}
|
|
else
|
|
{
|
|
*alen = *smax/8; /* never require the multiword hash */
|
|
*blen = (nkeys <= *smax*(5.0/8.0)) ? *smax/4 : *smax/2;
|
|
}
|
|
break;
|
|
case 19:
|
|
case 20:
|
|
*alen = (nkeys <= *smax*(5.0/8.0)) ? *smax/8 : *smax/2;
|
|
*blen = (nkeys <= *smax*(5.0/8.0)) ? *smax/4 : *smax/2;
|
|
break;
|
|
default:
|
|
*alen = *smax/2; /* just find a hash as quick as possible */
|
|
*blen = *smax/2; /* we'll be thrashing virtual memory at this size */
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
|
|
/*
|
|
** Try to find a perfect hash function.
|
|
** Return the successful initializer for the initial hash.
|
|
** Return 0 if no perfect hash could be found.
|
|
*/
|
|
void findhash(
|
|
bstuff **tabb, /* output, tab[] of the perfect hash, length *blen */
|
|
hstuff **tabh, /* output, table of keys indexed by hash value */
|
|
ub4 *alen, /* output, 0..alen-1 is range for a of (a,b) */
|
|
ub4 *blen, /* output, 0..blen-1 is range for b of (a,b) */
|
|
ub4 *salt, /* output, initializes initial hash */
|
|
gencode *final, /* code for final hash */
|
|
ub4 *scramble, /* input, hash = a^scramble[tab[b]] */
|
|
ub4 *smax, /* input, scramble[i] in 0..smax-1 */
|
|
key *keys, /* input, keys to hash */
|
|
ub4 nkeys, /* input, number of keys being hashed */
|
|
hashform *form) /* user directives */
|
|
{
|
|
ub4 bad_initkey; /* how many times did initkey fail? */
|
|
ub4 bad_perfect; /* how many times did perfect fail? */
|
|
ub4 trysalt; /* trial initializer for initial hash */
|
|
ub4 maxalen;
|
|
qstuff *tabq; /* table of stuff indexed by queue value, used by augment */
|
|
|
|
/* The case of (A,B) supplied by the user is a special case */
|
|
if (form->hashtype == AB_HT)
|
|
{
|
|
hash_ab(tabb, alen, blen, salt, final,
|
|
scramble, smax, keys, nkeys, form);
|
|
return;
|
|
}
|
|
|
|
/* guess initial values for smax, alen and blen */
|
|
*smax = ((ub4)1<<phash_log2(nkeys));
|
|
initalen(alen, blen, smax, nkeys, form);
|
|
|
|
scrambleinit(scramble, *smax);
|
|
|
|
maxalen = (form->perfect == MINIMAL_HP) ? *smax/2 : *smax;
|
|
|
|
/* allocate working memory */
|
|
*tabb = (bstuff *)yasm_xmalloc((size_t)(sizeof(bstuff)*(*blen)));
|
|
tabq = (qstuff *)yasm_xmalloc(sizeof(qstuff)*(*blen+1));
|
|
*tabh = (hstuff *)yasm_xmalloc(sizeof(hstuff)*(form->perfect == MINIMAL_HP ?
|
|
nkeys : *smax));
|
|
|
|
/* Actually find the perfect hash */
|
|
*salt = 0;
|
|
bad_initkey = 0;
|
|
bad_perfect = 0;
|
|
for (trysalt=1; ; ++trysalt)
|
|
{
|
|
ub4 rslinit;
|
|
/* Try to find distinct (A,B) for all keys */
|
|
|
|
rslinit = initkey(keys, nkeys, *tabb, *alen, *blen, *smax, trysalt,
|
|
form, final);
|
|
|
|
if (rslinit == 2)
|
|
{ /* initkey actually found a perfect hash, not just distinct (a,b) */
|
|
*salt = 1;
|
|
*blen = 0;
|
|
break;
|
|
}
|
|
else if (rslinit == 0)
|
|
{
|
|
/* didn't find distinct (a,b) */
|
|
if (++bad_initkey >= RETRY_INITKEY)
|
|
{
|
|
/* Try to put more bits in (A,B) to make distinct (A,B) more likely */
|
|
if (*alen < maxalen)
|
|
{
|
|
*alen *= 2;
|
|
}
|
|
else if (*blen < *smax)
|
|
{
|
|
*blen *= 2;
|
|
free(tabq);
|
|
free(*tabb);
|
|
*tabb = (bstuff *)yasm_xmalloc((size_t)(sizeof(bstuff)*(*blen)));
|
|
tabq = (qstuff *)yasm_xmalloc((size_t)(sizeof(qstuff)*(*blen+1)));
|
|
}
|
|
else
|
|
{
|
|
duplicates(*tabb, *blen, keys, form); /* check for duplicates */
|
|
fprintf(stderr, "fatal error: Cannot perfect hash: cannot find distinct (A,B)\n");
|
|
exit(EXIT_FAILURE);
|
|
}
|
|
bad_initkey = 0;
|
|
bad_perfect = 0;
|
|
}
|
|
continue; /* two keys have same (a,b) pair */
|
|
}
|
|
|
|
printf("found distinct (A,B) on attempt %ld\n", trysalt);
|
|
|
|
/* Given distinct (A,B) for all keys, build a perfect hash */
|
|
if (!perfect(*tabb, *tabh, tabq, *blen, *smax, scramble, nkeys, form))
|
|
{
|
|
if ((form->hashtype != INT_HT && ++bad_perfect >= RETRY_PERFECT) ||
|
|
(form->hashtype == INT_HT && ++bad_perfect >= RETRY_HEX))
|
|
{
|
|
if (*blen < *smax)
|
|
{
|
|
*blen *= 2;
|
|
free(*tabb);
|
|
free(tabq);
|
|
*tabb = (bstuff *)yasm_xmalloc((size_t)(sizeof(bstuff)*(*blen)));
|
|
tabq = (qstuff *)yasm_xmalloc((size_t)(sizeof(qstuff)*(*blen+1)));
|
|
--trysalt; /* we know this salt got distinct (A,B) */
|
|
}
|
|
else
|
|
{
|
|
fprintf(stderr, "fatal error: Cannot perfect hash: cannot build tab[]\n");
|
|
exit(EXIT_FAILURE);
|
|
}
|
|
bad_perfect = 0;
|
|
}
|
|
continue;
|
|
}
|
|
|
|
*salt = trysalt;
|
|
break;
|
|
}
|
|
|
|
printf("built perfect hash table of size %ld\n", *blen);
|
|
|
|
/* free working memory */
|
|
free((void *)tabq);
|
|
}
|
|
|
|
#if 0
|
|
/*
|
|
------------------------------------------------------------------------------
|
|
Input/output type routines
|
|
------------------------------------------------------------------------------
|
|
*/
|
|
|
|
/* get the list of keys */
|
|
static void getkeys(keys, nkeys, textroot, keyroot, form)
|
|
key **keys; /* list of all keys */
|
|
ub4 *nkeys; /* number of keys */
|
|
reroot *textroot; /* get space to store key text */
|
|
reroot *keyroot; /* get space for keys */
|
|
hashform *form; /* user directives */
|
|
{
|
|
key *mykey;
|
|
char *mytext;
|
|
mytext = (char *)renew(textroot);
|
|
*keys = 0;
|
|
*nkeys = 0;
|
|
while (fgets(mytext, MAXKEYLEN, stdin))
|
|
{
|
|
mykey = (key *)renew(keyroot);
|
|
if (form->mode == AB_HM)
|
|
{
|
|
sscanf(mytext, "%lx %lx ", &mykey->a_k, &mykey->b_k);
|
|
}
|
|
else if (form->mode == ABDEC_HM)
|
|
{
|
|
sscanf(mytext, "%ld %ld ", &mykey->a_k, &mykey->b_k);
|
|
}
|
|
else if (form->mode == HEX_HM)
|
|
{
|
|
sscanf(mytext, "%lx ", &mykey->hash_k);
|
|
}
|
|
else if (form->mode == DECIMAL_HM)
|
|
{
|
|
sscanf(mytext, "%ld ", &mykey->hash_k);
|
|
}
|
|
else
|
|
{
|
|
mykey->name_k = (ub1 *)mytext;
|
|
mytext = (char *)renew(textroot);
|
|
mykey->len_k = (ub4)(strlen((char *)mykey->name_k)-1);
|
|
}
|
|
mykey->next_k = *keys;
|
|
*keys = mykey;
|
|
++*nkeys;
|
|
}
|
|
redel(textroot, mytext);
|
|
}
|
|
|
|
/* make the .c file */
|
|
static void make_c(tab, smax, blen, scramble, final, form)
|
|
bstuff *tab; /* table indexed by b */
|
|
ub4 smax; /* range of scramble[] */
|
|
ub4 blen; /* b in 0..blen-1, power of 2 */
|
|
ub4 *scramble; /* used in final hash */
|
|
gencode *final; /* code for the final hash */
|
|
hashform *form; /* user directives */
|
|
{
|
|
ub4 i;
|
|
FILE *f;
|
|
f = fopen("phash.c", "w");
|
|
fprintf(f, "/* table for the mapping for the perfect hash */\n");
|
|
fprintf(f, "#include \"lookupa.h\"\n");
|
|
fprintf(f, "\n");
|
|
if (blen >= USE_SCRAMBLE)
|
|
{
|
|
fprintf(f, "/* A way to make the 1-byte values in tab bigger */\n");
|
|
if (smax > UB2MAXVAL+1)
|
|
{
|
|
fprintf(f, "unsigned long scramble[] = {\n");
|
|
for (i=0; i<=UB1MAXVAL; i+=4)
|
|
fprintf(f, "0x%.8lx, 0x%.8lx, 0x%.8lx, 0x%.8lx,\n",
|
|
scramble[i+0], scramble[i+1], scramble[i+2], scramble[i+3]);
|
|
}
|
|
else
|
|
{
|
|
fprintf(f, "unsigned short scramble[] = {\n");
|
|
for (i=0; i<=UB1MAXVAL; i+=8)
|
|
fprintf(f,
|
|
"0x%.4lx, 0x%.4lx, 0x%.4lx, 0x%.4lx, 0x%.4lx, 0x%.4lx, 0x%.4lx, 0x%.4lx,\n",
|
|
scramble[i+0], scramble[i+1], scramble[i+2], scramble[i+3],
|
|
scramble[i+4], scramble[i+5], scramble[i+6], scramble[i+7]);
|
|
}
|
|
fprintf(f, "};\n");
|
|
fprintf(f, "\n");
|
|
}
|
|
if (blen > 0)
|
|
{
|
|
fprintf(f, "/* small adjustments to _a_ to make values distinct */\n");
|
|
|
|
if (smax <= UB1MAXVAL+1 || blen >= USE_SCRAMBLE)
|
|
fprintf(f, "unsigned char tab[] = {\n");
|
|
else
|
|
fprintf(f, "unsigned short tab[] = {\n");
|
|
|
|
if (blen < 16)
|
|
{
|
|
for (i=0; i<blen; ++i) fprintf(f, "%3d,", scramble[tab[i].val_b]);
|
|
}
|
|
else if (blen <= 1024)
|
|
{
|
|
for (i=0; i<blen; i+=16)
|
|
fprintf(f, "%ld,%ld,%ld,%ld,%ld,%ld,%ld,%ld,%ld,%ld,%ld,%ld,%ld,%ld,%ld,%ld,\n",
|
|
scramble[tab[i+0].val_b], scramble[tab[i+1].val_b],
|
|
scramble[tab[i+2].val_b], scramble[tab[i+3].val_b],
|
|
scramble[tab[i+4].val_b], scramble[tab[i+5].val_b],
|
|
scramble[tab[i+6].val_b], scramble[tab[i+7].val_b],
|
|
scramble[tab[i+8].val_b], scramble[tab[i+9].val_b],
|
|
scramble[tab[i+10].val_b], scramble[tab[i+11].val_b],
|
|
scramble[tab[i+12].val_b], scramble[tab[i+13].val_b],
|
|
scramble[tab[i+14].val_b], scramble[tab[i+15].val_b]);
|
|
}
|
|
else if (blen < USE_SCRAMBLE)
|
|
{
|
|
for (i=0; i<blen; i+=8)
|
|
fprintf(f, "%ld,%ld,%ld,%ld,%ld,%ld,%ld,%ld,\n",
|
|
scramble[tab[i+0].val_b], scramble[tab[i+1].val_b],
|
|
scramble[tab[i+2].val_b], scramble[tab[i+3].val_b],
|
|
scramble[tab[i+4].val_b], scramble[tab[i+5].val_b],
|
|
scramble[tab[i+6].val_b], scramble[tab[i+7].val_b]);
|
|
}
|
|
else
|
|
{
|
|
for (i=0; i<blen; i+=16)
|
|
fprintf(f, "%ld,%ld,%ld,%ld,%ld,%ld,%ld,%ld,%ld,%ld,%ld,%ld,%ld,%ld,%ld,%ld,\n",
|
|
tab[i+0].val_b, tab[i+1].val_b,
|
|
tab[i+2].val_b, tab[i+3].val_b,
|
|
tab[i+4].val_b, tab[i+5].val_b,
|
|
tab[i+6].val_b, tab[i+7].val_b,
|
|
tab[i+8].val_b, tab[i+9].val_b,
|
|
tab[i+10].val_b, tab[i+11].val_b,
|
|
tab[i+12].val_b, tab[i+13].val_b,
|
|
tab[i+14].val_b, tab[i+15].val_b);
|
|
}
|
|
fprintf(f, "};\n");
|
|
fprintf(f, "\n");
|
|
}
|
|
fprintf(f, "/* The hash function */\n");
|
|
switch(form->mode)
|
|
{
|
|
case NORMAL_HM:
|
|
fprintf(f, "ub4 phash(key, len)\n");
|
|
fprintf(f, "char *key;\n");
|
|
fprintf(f, "int len;\n");
|
|
break;
|
|
case INLINE_HM:
|
|
case HEX_HM:
|
|
case DECIMAL_HM:
|
|
fprintf(f, "ub4 phash(val)\n");
|
|
fprintf(f, "ub4 val;\n");
|
|
break;
|
|
case AB_HM:
|
|
case ABDEC_HM:
|
|
fprintf(f, "ub4 phash(a,b)\n");
|
|
fprintf(f, "ub4 a;\n");
|
|
fprintf(f, "ub4 b;\n");
|
|
break;
|
|
}
|
|
fprintf(f, "{\n");
|
|
for (i=0; i<final->used; ++i)
|
|
fprintf(f, final->line[i]);
|
|
fprintf(f, " return rsl;\n");
|
|
fprintf(f, "}\n");
|
|
fprintf(f, "\n");
|
|
fclose(f);
|
|
}
|
|
|
|
/*
|
|
------------------------------------------------------------------------------
|
|
Read in the keys, find the hash, and write the .c and .h files
|
|
------------------------------------------------------------------------------
|
|
*/
|
|
static void driver(form)
|
|
hashform *form; /* user directives */
|
|
{
|
|
ub4 nkeys; /* number of keys */
|
|
key *keys; /* head of list of keys */
|
|
bstuff *tab; /* table indexed by b */
|
|
ub4 smax; /* scramble[] values in 0..smax-1, a power of 2 */
|
|
ub4 alen; /* a in 0..alen-1, a power of 2 */
|
|
ub4 blen; /* b in 0..blen-1, a power of 2 */
|
|
ub4 salt; /* a parameter to the hash function */
|
|
reroot *textroot; /* MAXKEYLEN-character text lines */
|
|
reroot *keyroot; /* source of keys */
|
|
gencode final; /* code for final hash */
|
|
ub4 i;
|
|
ub4 scramble[SCRAMBLE_LEN]; /* used in final hash function */
|
|
char buf[10][80]; /* buffer for generated code */
|
|
char *buf2[10]; /* also for generated code */
|
|
|
|
/* set up memory sources */
|
|
textroot = remkroot((size_t)MAXKEYLEN);
|
|
keyroot = remkroot(sizeof(key));
|
|
|
|
/* set up code for final hash */
|
|
final.line = buf2;
|
|
final.used = 0;
|
|
final.len = 10;
|
|
for (i=0; i<10; ++i) final.line[i] = buf[i];
|
|
|
|
/* read in the list of keywords */
|
|
getkeys(&keys, &nkeys, textroot, keyroot, form);
|
|
printf("Read in %ld keys\n",nkeys);
|
|
|
|
/* find the hash */
|
|
findhash(&tab, &alen, &blen, &salt, &final,
|
|
scramble, &smax, keys, nkeys, form);
|
|
|
|
/* generate the phash.c file */
|
|
make_c(tab, smax, blen, scramble, &final, form);
|
|
printf("Wrote phash.c\n");
|
|
|
|
/* clean up memory sources */
|
|
refree(textroot);
|
|
refree(keyroot);
|
|
free((void *)tab);
|
|
printf("Cleaned up\n");
|
|
}
|
|
|
|
|
|
/* Interpret arguments and call the driver */
|
|
/* See usage_error for the expected arguments */
|
|
int main(argc, argv)
|
|
int argc;
|
|
char **argv;
|
|
{
|
|
int mode_given = FALSE;
|
|
int minimal_given = FALSE;
|
|
int speed_given = FALSE;
|
|
hashform form;
|
|
char *c;
|
|
|
|
/* default behavior */
|
|
form.mode = NORMAL_HM;
|
|
form.hashtype = STRING_HT;
|
|
form.perfect = MINIMAL_HP;
|
|
form.speed = SLOW_HS;
|
|
|
|
/* Generate the [minimal] perfect hash */
|
|
driver(&form);
|
|
|
|
return EXIT_SUCCESS;
|
|
}
|
|
#endif
|