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#include <stdlib.h>
#include <string.h>
#include <search.h>
/*
open addressing hash table with 2^n table size
quadratic probing is used in case of hash collision
tab indices and hash are size_t
after resize fails with ENOMEM the state of tab is still usable
with the posix api items cannot be iterated and length cannot be queried
*/
#define MINSIZE 8
#define MAXSIZE ((size_t)-1/2 + 1)
struct elem {
ENTRY item;
size_t hash;
};
static size_t mask;
static size_t used;
static struct elem *tab;
static size_t keyhash(char *k)
{
unsigned char *p = (void *)k;
size_t h = 0;
while (*p)
h = 31*h + *p++;
return h;
}
static int resize(size_t nel)
{
size_t newsize;
size_t i, j;
struct elem *e, *newe;
struct elem *oldtab = tab;
struct elem *oldend = tab + mask + 1;
if (nel > MAXSIZE)
nel = MAXSIZE;
for (newsize = MINSIZE; newsize < nel; newsize *= 2);
tab = calloc(newsize, sizeof *tab);
if (!tab) {
tab = oldtab;
return 0;
}
mask = newsize - 1;
if (!oldtab)
return 1;
for (e = oldtab; e < oldend; e++)
if (e->item.key) {
for (i=e->hash,j=1; ; i+=j++) {
newe = tab + (i & mask);
if (!newe->item.key)
break;
}
*newe = *e;
}
free(oldtab);
return 1;
}
int hcreate(size_t nel)
{
mask = 0;
used = 0;
tab = 0;
return resize(nel);
}
void hdestroy(void)
{
free(tab);
tab = 0;
mask = 0;
used = 0;
}
static struct elem *lookup(char *key, size_t hash)
{
size_t i, j;
struct elem *e;
for (i=hash,j=1; ; i+=j++) {
e = tab + (i & mask);
if (!e->item.key ||
(e->hash==hash && strcmp(e->item.key, key)==0))
break;
}
return e;
}
ENTRY *hsearch(ENTRY item, ACTION action)
{
size_t hash = keyhash(item.key);
struct elem *e = lookup(item.key, hash);
if (e->item.key)
return &e->item;
if (action == FIND)
return 0;
e->item = item;
e->hash = hash;
if (++used > mask - mask/4) {
if (!resize(2*used)) {
used--;
e->item.key = 0;
return 0;
}
e = lookup(item.key, hash);
}
return &e->item;
}
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