491 lines
12 KiB
C
491 lines
12 KiB
C
/* Compile time switches:
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MULT - use a multiplicative hashing function.
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DIV - use the remainder mod table size as a hashing function.
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CHAINED - use a linked list to resolve collisions.
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OPEN - use open addressing to resolve collisions.
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BRENT - use Brent's modification to improve the OPEN algorithm.
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SORTUP - CHAINED list is sorted in increasing order.
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SORTDOWN - CHAINED list is sorted in decreasing order.
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START - CHAINED list with entries appended at front.
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DRIVER - compile in a main program to drive the tests.
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DEBUG - compile some debugging printout statements.
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USCR - user supplied comparison routine.
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*/
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#include <stdio.h>
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#define SUCCEED 0
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#define FAIL 1
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#define TRUE 1
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#define FALSE 0
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#define repeat for(;;)
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#define until(A) if(A) break;
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#ifdef OPEN
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# undef CHAINED
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#else
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#ifndef CHAINED
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# define OPEN
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#endif
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#endif
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#ifdef MULT
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# undef DIV
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#else
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#ifndef DIV
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# define MULT
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#endif
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#endif
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#ifdef START
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# undef SORTUP
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# undef SORTDOWN
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#else
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#ifdef SORTUP
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# undef SORTDOWN
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#endif
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#endif
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#ifdef USCR
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# define COMPARE(A, B) (* hcompar)((A), (B))
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extern int (* hcompar)();
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#else
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# define COMPARE(A, B) strcmp((A), (B))
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#endif
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#ifdef MULT
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# define SHIFT ((bitsper * sizeof(int)) - m) /* Shift factor */
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# define FACTOR 035761254233 /* Magic multiplication factor */
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# define HASH hashm /* Multiplicative hash function */
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# define HASH2 hash2m /* Secondary hash function */
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static unsigned int bitsper; /* Bits per byte */
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static unsigned int hashm();
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static unsigned int hash2m();
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#else
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#ifdef DIV
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# define HASH hashd /* Division hashing routine */
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# define HASH2(A) 1 /* Secondary hash function */
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static unsigned int hashd();
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#endif
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#endif
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typedef enum {
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FIND, /* Find, if present */
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ENTER /* Find; enter if not present */
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} ACTION;
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typedef char *POINTER;
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typedef struct entry { /* Hash table entry */
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POINTER key;
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POINTER data;
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} ENTRY;
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#ifdef CHAINED
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typedef struct node { /* Part of the linked list of entries */
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ENTRY item;
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struct node *next;
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} NODE;
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typedef NODE *TABELEM;
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static NODE **table; /* The address of the hash table */
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static ENTRY *build();
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#else
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#ifdef OPEN
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typedef ENTRY TABELEM; /* What the table contains (TABle ELEMents) */
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static TABELEM *table; /* The address of the hash table */
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static unsigned int count = 0; /* Number of entries in hash table */
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#endif
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#endif
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static unsigned int length; /* Size of the hash table */
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static unsigned int m; /* Log base 2 of length */
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static unsigned int prcnt; /* Number of probes this item */
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extern void free();
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extern int printf(), fprintf();
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extern char *malloc(), *calloc(), *strcpy();
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int hcreate();
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void hdestroy();
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ENTRY *hsearch();
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static unsigned int crunch();
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#ifdef DRIVER
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static void hdump();
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main()
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{
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char line[80]; /* Room for the input line */
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int i = 0; /* Data generator */
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ENTRY *res; /* Result of hsearch */
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ENTRY *new; /* Test entry */
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if(hcreate(5))
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printf("Length = %u, m = %u\n", length, m);
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else {
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fprintf(stderr, "Out of core\n");
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exit(FAIL);
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}
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repeat {
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hdump();
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printf("Enter a probe: ");
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until (EOF == scanf("%s", line));
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#ifdef DEBUG
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printf("%s, ", line);
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printf("division: %d, ", hashd(line));
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printf("multiplication: %d\n", hashm(line));
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#endif
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new = (ENTRY *) malloc(sizeof(ENTRY));
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if(new == NULL) {
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fprintf(stderr, "Out of core \n");
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exit(FAIL);
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}
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else {
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new->key = malloc((unsigned) strlen(line) + 1);
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if(new->key == NULL) {
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fprintf(stderr, "Out of core \n");
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exit(FAIL);
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}
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strcpy(new->key, line);
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new->data = malloc(sizeof(int));
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if(new->data == NULL) {
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fprintf(stderr, "Out of core \n");
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exit(FAIL);
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}
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*new->data = i++;
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}
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res = hsearch(*new, ENTER);
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printf("The number of probes required was %d\n", prcnt);
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if(res == (ENTRY *) 0)
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printf("Table is full\n");
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else {
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printf("Success: ");
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printf("Key = %s, Value = %d\n", res->key, *res->data);
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}
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}
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exit(SUCCEED);
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}
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#endif
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int
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hcreate(size) /* Create a hash table no smaller than size */
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int size; /* Minimum size for hash table */
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{
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unsigned int unsize; /* Holds the shifted size */
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if(size <= 0)
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return(FALSE);
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unsize = size; /* +1 for empty table slot; -1 for ceiling */
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length = 1; /* Maximum entries in tabbe */
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m = 0; /* Log2 length */
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while(unsize) {
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unsize >>= 1;
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length <<= 1;
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m++;
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}
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table = (TABELEM *) calloc(length, sizeof(TABELEM));
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return(table != NULL);
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}
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void
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hdestroy() /* Reset the module to its initial state */
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{
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free((POINTER) table);
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#ifdef OPEN
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count = 0;
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#endif
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}
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#ifdef OPEN
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/* Hash search of a fixed-capacity table. Open addressing used to
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resolve collisions. Algorithm modified from Knuth, Volume 3,
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section 6.4, algorithm D. Labels flag corresponding actions.
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*/
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ENTRY
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*hsearch(item, action) /* Find or insert the item into the table */
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ENTRY item; /* Item to be inserted or found */
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ACTION action; /* FIND or ENTER */
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{
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unsigned int i; /* Insertion index */
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unsigned int c; /* Secondary probe displacement */
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prcnt = 1;
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/* D1: */
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i = HASH(item.key); /* Primary hash on key */
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#ifdef DEBUG
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if(action == ENTER)
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printf("hash = %o\n", i);
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#endif
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/* D2: */
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if(table[i].key == NULL) /* Empty slot? */
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goto D6;
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else if(COMPARE(table[i].key, item.key) == 0) /* Match? */
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return(&table[i]);
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/* D3: */
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c = HASH2(item.key); /* No match => compute secondary hash */
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#ifdef DEBUG
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if(action == ENTER)
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printf("hash2 = %o\n", c);
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#endif
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D4:
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i = (i + c) % length; /* Advance to next slot */
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prcnt++;
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/* D5: */
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if(table[i].key == NULL) /* Empty slot? */
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goto D6;
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else if(COMPARE(table[i].key, item.key) == 0) /* Match? */
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return(&table[i]);
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else
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goto D4;
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D6: if(action == FIND) /* Insert if requested */
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return((ENTRY *) NULL);
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if(count == (length - 1)) /* Table full? */
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return((ENTRY *) 0);
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#ifdef BRENT
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/* Brent's variation of the open addressing algorithm. Do extra
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work during insertion to speed retrieval. May require switching
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of previously placed items. Adapted from Knuth, Volume 3, section
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4.6 and Brent's article in CACM, volume 10, #2, February 1973.
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*/
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{ unsigned int p0 = HASH(item.key); /* First probe index */
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unsigned int c0 = HASH2(item.key); /* Main branch increment */
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unsigned int r = prcnt - 1; /* Current minimum distance */
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unsigned int j; /* Counts along main branch */
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unsigned int k; /* Counts along secondary branch */
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unsigned int curj; /* Current best main branch site */
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unsigned int curpos; /* Current best table index */
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unsigned int pj; /* Main branch indices */
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unsigned int cj; /* Secondary branch increment distance*/
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unsigned int pjk; /* Secondary branch probe indices */
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if(prcnt >= 3) {
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for(j = 0; j < prcnt; j++) { /* Count along main branch */
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pj = (p0 + j * c0) % length; /* New main branch index */
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cj = HASH2(table[pj].key); /* Secondary branch incr. */
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for(k=1; j+k <= r; k++) { /* Count on secondary branch*/
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pjk = (pj + k * cj) % length; /* Secondary probe */
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if(table[pjk].key == NULL) { /* Improvement found */
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r = j + k; /* Decrement upper bound */
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curj = pj; /* Save main probe index */
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curpos = pjk; /* Save secondeary index */
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}
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}
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}
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if(r != prcnt - 1) { /* If an improvement occurred */
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table[curpos] = table[curj]; /* Old key to new site */
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#ifdef DEBUG
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printf("Switch curpos = %o, curj = %o, oldi = %o\n",
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curj, curpos, i);
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#endif
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i = curj;
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}
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}
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}
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#endif
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count++; /* Increment table occupancy count */
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table[i] = item; /* Save item */
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return(&table[i]); /* Address of item is returned */
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}
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#endif
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#ifdef USCR
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# ifdef DRIVER
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static int
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compare(a, b)
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POINTER a;
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POINTER b;
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{
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return(strcmp(a, b));
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}
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int (* hcompar)() = compare;
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# endif
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#endif
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#ifdef CHAINED
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# ifdef SORTUP
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# define STRCMP(A, B) (COMPARE((A), (B)) > 0)
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# else
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# ifdef SORTDOWN
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# define STRCMP(A, B) (COMPARE((A), (B)) < 0)
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# else
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# define STRCMP(A, B) (COMPARE((A), (B)) != 0)
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# endif
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# endif
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ENTRY
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*hsearch(item, action) /* Chained search with sorted lists */
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ENTRY item; /* Item to be inserted or found */
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ACTION action; /* FIND or ENTER */
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{
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NODE *p; /* Searches through the linked list */
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NODE **q; /* Where to store the pointer to a new NODE */
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unsigned int i; /* Result of hash */
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int res; /* Result of string comparison */
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prcnt = 1;
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i = HASH(item.key); /* Table[i] contains list head */
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if(table[i] == (NODE*)NULL) { /* List has not yet been begun */
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if(action == FIND)
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return((ENTRY *) NULL);
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else
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return(build(&table[i], (NODE *) NULL, item));
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}
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else { /* List is not empty */
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q = &table[i];
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p = table[i];
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while(p != NULL && (res = STRCMP(item.key, p->item.key))) {
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prcnt++;
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q = &(p->next);
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p = p->next;
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}
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if(p != NULL && res == 0) /* Item has been found */
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return(&(p->item));
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else { /* Item is not yet on list */
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if(action == FIND)
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return((ENTRY *) NULL);
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else
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#ifdef START
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return(build(&table[i], table[i], item));
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#else
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return(build(q, p, item));
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#endif
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}
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}
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}
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static ENTRY
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*build(last, next, item)
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NODE **last; /* Where to store in last list item */
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NODE *next; /* Link to next list item */
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ENTRY item; /* Item to be kept in node */
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{
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NODE *p = (NODE *) malloc(sizeof(NODE));
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if(p != NULL) {
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p->item = item;
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*last = p;
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p->next = next;
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return(&(p->item));
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}
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else
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return(NULL);
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}
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#endif
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#ifdef DIV
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static unsigned int
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hashd(key) /* Division hashing scheme */
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POINTER key; /* Key to be hashed */
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{
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return(crunch(key) % length);
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}
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#else
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#ifdef MULT
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/*
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NOTE: The following algorithm only works on machines where
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the results of multiplying two integers is the least
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significant part of the double word integer required to hold
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the result. It is adapted from Knuth, Volume 3, section 6.4.
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*/
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static unsigned int
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hashm(key) /* Multiplication hashing scheme */
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POINTER key; /* Key to be hashed */
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{
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static int first = TRUE; /* TRUE on the first call only */
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if(first) { /* Compute the number of bits in a byte */
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unsigned char c = ~0; /* A byte full of 1's */
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bitsper = 0;
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while(c) { /* Shift until no more 1's */
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c = c >> 1;
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bitsper++; /* Count number of shifts */
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}
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first = FALSE;
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}
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return((int) (((unsigned) (crunch(key) * FACTOR)) >> SHIFT));
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}
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/*
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* Secondary hashing, for use with multiplicitive hashing scheme.
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* Adapted from Knuth, Volume 3, section 6.4.
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*/
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static unsigned int
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hash2m(key) /* Secondary hashing routine */
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POINTER key; /* String to be hashed */
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{
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return((int) (((unsigned) ((crunch(key) * FACTOR) << m) >> SHIFT) | 1));
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}
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#endif
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#endif
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static unsigned int
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crunch(key) /* Convert multicharacter key to unsigned int */
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POINTER key;
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{
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unsigned int sum = 0; /* Results */
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int s; /* Length of the key */
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for(s = 0; *key; s++) /* Simply add up the bytes */
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sum += *key++;
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return(sum + s);
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}
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#ifdef DRIVER
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static void
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hdump() /* Dumps loc, data, probe count, key */
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{
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unsigned int i; /* Counts table slots */
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#ifdef OPEN
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unsigned int sum = 0; /* Counts probes */
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#else
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#ifdef CHAINED
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NODE *a; /* Current Node on list */
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#endif
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#endif
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for(i = 0; i < length; i++)
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#ifdef OPEN
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if(table[i].key == NULL)
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printf("%o.\t-,\t-,\t(NULL)\n", i);
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else {
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unsigned int oldpr = prcnt; /* Save current probe count */
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hsearch(table[i], FIND);
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sum += prcnt;
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printf("%o.\t%d,\t%d,\t%s\n", i,
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*table[i].data, prcnt, table[i].key);
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prcnt = oldpr;
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}
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printf("Total probes = %d\n", sum);
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#else
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#ifdef CHAINED
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if(table[i] == NULL)
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printf("%o.\t-,\t-,\t(NULL)\n", i);
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else {
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printf("%o.", i);
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for(a = table[i]; a != NULL; a = a->next)
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printf("\t%d,\t%#0.4x,\t%s\n",
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*a->item.data, a, a->item.key);
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}
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#endif
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#endif
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}
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#endif
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