blob: 299821caf60a5f676d3875b73dae42aa16da5b55 [file] [log] [blame]
** $Id: ltable.c,v 1.38 2000/03/29 20:19:20 roberto Exp roberto $
** Lua tables (hash)
** See Copyright Notice in lua.h
** Implementation of tables (aka arrays, objects, or hash tables);
** uses a mix of chained scatter table with Brent's variation.
** A main invariant of these tables is that, if an element is not
** in its main position (i.e. the `original' position that its hash gives
** to it), then the colliding element is in its own main position.
** In other words, there are collisions only when two elements have the
** same main position (i.e. the same hash values for that table size).
** Because of that, the load factor of these tables can be 100% without
** performance penalties.
#include "lauxlib.h"
#include "lmem.h"
#include "lobject.h"
#include "lstate.h"
#include "ltable.h"
#include "lua.h"
#define gcsize(L, n) numblocks(L, n*2, sizeof(Hash))
#define TagDefault TAG_TABLE
** returns the `main' position of an element in a table (that is, the index
** of its hash value)
Node *luaH_mainposition (const Hash *t, const TObject *key) {
unsigned long h;
switch (ttype(key)) {
h = (unsigned long)(long)nvalue(key);
h = tsvalue(key)->hash;
h = IntPoint(L, avalue(key));
h = IntPoint(L, clvalue(key));
return NULL; /* invalid key */
LUA_ASSERT(L, h%(unsigned int)t->size == (h&((unsigned int)t->size-1)),
"a&(x-1) == a%x, for x power of 2");
return &t->node[h&((unsigned int)t->size-1)];
const TObject *luaH_get (lua_State *L, const Hash *t, const TObject *key) {
Node *n = luaH_mainposition(t, key);
if (!n)
lua_error(L, "unexpected type to index table");
else do {
if (luaO_equalObj(key, &n->key))
return &n->val;
n = n->next;
} while (n);
return &luaO_nilobject; /* key not found */
int luaH_pos (lua_State *L, const Hash *t, const TObject *key) {
const TObject *v = luaH_get(L, t, key);
return (v == &luaO_nilobject) ? -1 : /* key not found */
(int)(((const char *)v - (const char *)(&t->node[0].val))/sizeof(Node));
static Node *hashnodecreate (lua_State *L, int nhash) {
Node *v = luaM_newvector(L, nhash, Node);
int i;
for (i=0; i<nhash; i++) {
ttype(&v[i].key) = ttype(&v[i].val) = TAG_NIL;
v[i].next = NULL;
return v;
static void setnodevector (lua_State *L, Hash *t, int size) {
t->node = hashnodecreate(L, size);
t->size = size;
t->firstfree = &t->node[size-1]; /* first free position to be used */
L->nblocks += gcsize(L, size);
Hash *luaH_new (lua_State *L, int size) {
Hash *t = luaM_new(L, Hash);
setnodevector(L, t, luaO_power2(size));
t->htag = TagDefault;
t->next = L->roottable;
L->roottable = t;
t->marked = 0;
return t;
void luaH_free (lua_State *L, Hash *t) {
L->nblocks -= gcsize(L, t->size);
luaM_free(L, t->node);
luaM_free(L, t);
static int newsize (const Hash *t) {
Node *v = t->node;
int size = t->size;
int realuse = 0;
int i;
for (i=0; i<size; i++) {
if (ttype(&v[i].val) != TAG_NIL)
return luaO_power2(realuse+realuse/4+1);
static void rehash (lua_State *L, Hash *t) {
int oldsize = t->size;
Node *nold = t->node;
int i;
L->nblocks -= gcsize(L, oldsize);
setnodevector(L, t, newsize(t)); /* create new array of nodes */
for (i=0; i<oldsize; i++) {
Node *old = nold+i;
if (ttype(&old->val) != TAG_NIL)
luaH_set(L, t, &old->key, &old->val);
luaM_free(L, nold); /* free old array */
** sets a pair key-value in a hash table; first, check whether key is
** already present; if not, check whether key's main position is free;
** if not, check whether colliding node is in its main position or not;
** if it is not, move colliding node to an empty place and put new pair
** in its main position; otherwise (colliding node is in its main position),
** new pair goes to an empty position.
** Tricky point: the only place where an old element is moved is when
** we move the colliding node to an empty place; nevertheless, its old
** value is still in that position until we set the value for the new
** pair; therefore, even when `val' points to an element of this table
** (this happens when we use `luaH_move'), there is no problem.
void luaH_set (lua_State *L, Hash *t, const TObject *key, const TObject *val) {
Node *mp = luaH_mainposition(t, key);
Node *n = mp;
if (!mp)
lua_error(L, "unexpected type to index table");
do { /* check whether `key' is somewhere in the chain */
if (luaO_equalObj(key, &n->key)) {
n->val = *val; /* update value */
return; /* that's all */
else n = n->next;
} while (n);
/* `key' not found; must insert it */
if (ttype(&mp->key) != TAG_NIL) { /* main position is not free? */
Node *othern; /* main position of colliding node */
n = t->firstfree; /* get a free place */
/* is colliding node out of its main position? (can only happens if
its position if after "firstfree") */
if (mp > n && (othern=luaH_mainposition(t, &mp->key)) != mp) {
/* yes; move colliding node into free position */
while (othern->next != mp) othern = othern->next; /* find previous */
othern->next = n; /* redo the chain with `n' in place of `mp' */
*n = *mp; /* copy colliding node into free pos. (mp->next also goes) */
mp->next = NULL; /* now `mp' is free */
else { /* colliding node is in its own main position */
/* new node will go into free position */
n->next = mp->next; /* chain new position */
mp->next = n;
mp = n;
mp->key = *key;
mp->val = *val;
for (;;) { /* check free places */
if (ttype(&t->firstfree->key) == TAG_NIL)
return; /* OK; table still has a free place */
else if (t->firstfree == t->node) break; /* cannot decrement from here */
else (t->firstfree)--;
rehash(L, t); /* no more free places */
void luaH_setint (lua_State *L, Hash *t, int key, const TObject *val) {
TObject index;
ttype(&index) = TAG_NUMBER;
nvalue(&index) = key;
luaH_set(L, t, &index, val);
const TObject *luaH_getint (lua_State *L, const Hash *t, int key) {
TObject index;
ttype(&index) = TAG_NUMBER;
nvalue(&index) = key;
return luaH_get(L, t, &index);