133 lines
5.6 KiB
C
133 lines
5.6 KiB
C
/*
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------------------------------------------------------------------------------
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perfect.h: code to generate code for a hash for perfect hashing.
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(c) Bob Jenkins, September 1996
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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.h
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------------------------------------------------------------------------------
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*/
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#ifndef STANDARD
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#include "standard.h"
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#endif
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#ifndef PERFECT
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#define PERFECT
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#define MAXKEYLEN 30 /* maximum length of a key */
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#define USE_SCRAMBLE 4096 /* use scramble if blen >= USE_SCRAMBLE */
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#define SCRAMBLE_LEN ((ub4)1<<16) /* length of *scramble* */
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#define RETRY_INITKEY 2048 /* number of times to try to find distinct (a,b) */
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#define RETRY_PERFECT 1 /* number of times to try to make a perfect hash */
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#define RETRY_HEX 200 /* RETRY_PERFECT when hex keys given */
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/* the generated code for the final hash, assumes initial hash is done */
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struct gencode
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{
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char **line; /* array of text lines, 80 bytes apiece */
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/*
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* The code placed here must declare "ub4 rsl"
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* and assign it the value of the perfect hash using the function inputs.
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* Later code will be tacked on which returns rsl or manipulates it according
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* to the user directives.
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*
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* This code is at the top of the routine; it may and must declare any
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* local variables it needs.
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*
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* Each way of filling in **line should be given a comment that is a unique
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* tag. A testcase named with that tag should also be found which tests
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* the generated code.
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*/
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ub4 len; /* number of lines available for final hash */
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ub4 used; /* number of lines used by final hash */
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ub4 lowbit; /* for HEX, lowest interesting bit */
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ub4 highbit; /* for HEX, highest interesting bit */
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ub4 diffbits; /* bits which differ for some key */
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ub4 i,j,k,l,m,n,o; /* state machine used in hexn() */
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};
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typedef struct gencode gencode;
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/* user directives: perfect hash? minimal perfect hash? input is an int? */
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struct hashform
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{
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enum {
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NORMAL_HM, /* key is a string */
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INLINE_HM, /* user will do initial hash, we must choose salt for them */
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HEX_HM, /* key to be hashed is a hexidecimal 4-byte integer */
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DECIMAL_HM, /* key to be hashed is a decimal 4-byte integer */
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AB_HM, /* key to be hashed is "A B", where A and B are (A,B) in hex */
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ABDEC_HM /* like AB_HM, but in decimal */
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} mode;
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enum {
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STRING_HT, /* key is a string */
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INT_HT, /* key is an integer */
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AB_HT /* dunno what key is, but input is distinct (A,B) pair */
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} hashtype;
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enum {
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NORMAL_HP, /* just find a perfect hash */
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MINIMAL_HP /* find a minimal perfect hash */
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} perfect;
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enum {
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FAST_HS, /* fast mode */
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SLOW_HS /* slow mode */
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} speed;
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};
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typedef struct hashform hashform;
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/* representation of a key */
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struct key
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{
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char *name_k; /* the actual key */
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ub4 len_k; /* the length of the actual key */
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ub4 hash_k; /* the initial hash value for this key */
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struct key *next_k; /* next key */
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/* beyond this point is mapping-dependent */
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ub4 a_k; /* a, of the key maps to (a,b) */
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ub4 b_k; /* b, of the key maps to (a,b) */
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struct key *nextb_k; /* next key with this b */
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};
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typedef struct key key;
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/* things indexed by b of original (a,b) pair */
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struct bstuff
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{
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ub2 val_b; /* hash=a^tabb[b].val_b */
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key *list_b; /* tabb[i].list_b is list of keys with b==i */
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ub4 listlen_b; /* length of list_b */
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ub4 water_b; /* high watermark of who has visited this map node */
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};
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typedef struct bstuff bstuff;
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/* things indexed by final hash value */
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struct hstuff
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{
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key *key_h; /* tabh[i].key_h is the key with a hash of i */
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};
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typedef struct hstuff hstuff;
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/* things indexed by queue position */
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struct qstuff
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{
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bstuff *b_q; /* b that currently occupies this hash */
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ub4 parent_q; /* queue position of parent that could use this hash */
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ub2 newval_q; /* what to change parent tab[b] to to use this hash */
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ub2 oldval_q; /* original value of tab[b] */
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};
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typedef struct qstuff qstuff;
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/* return ceiling(log based 2 of x) */
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ub4 phash_log2(ub4 x);
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/* Given the keys, scramble[], and hash mode, find the perfect hash */
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void findhash(bstuff **tabb, hstuff **tabh, ub4 *alen, ub4 *blen, ub4 *salt,
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gencode *final, ub4 *scramble, ub4 *smax, key *keys, ub4 nkeys,
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hashform *form);
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/* private, but in a different file because it's excessively verbose */
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int inithex(key *keys, ub4 nkeys, ub4 alen, ub4 blen, ub4 smax, ub4 salt,
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gencode *final, hashform *form);
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#endif /* PERFECT */
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