src/ltable.c

   1 /*
   2 ** $Id: ltable.c,v 2.32.1.2 2007/12/28 15:32:23 roberto Exp $
   3 ** Lua tables (hash)
   4 ** See Copyright Notice in lua.h
   5 */
   6
   7
   8 /*
   9 ** Implementation of tables (aka arrays, objects, or hash tables).
  10 ** Tables keep its elements in two parts: an array part and a hash part.
  11 ** Non-negative integer keys are all candidates to be kept in the array
  12 ** part. The actual size of the array is the largest `n' such that at
  13 ** least half the slots between 0 and n are in use.
  14 ** Hash uses a mix of chained scatter table with Brent's variation.
  15 ** A main invariant of these tables is that, if an element is not
  16 ** in its main position (i.e. the `original' position that its hash gives
  17 ** to it), then the colliding element is in its own main position.
  18 ** Hence even when the load factor reaches 100%, performance remains good.
  19 */
  20
  21 #include <math.h>
  22 #include <string.h>
  23
  24 #define ltable_c
  25 #define LUA_CORE
  26
  27 #include "lua.h"
  28
  29 #include "ldebug.h"
  30 #include "ldo.h"
  31 #include "lgc.h"
  32 #include "lmem.h"
  33 #include "lobject.h"
  34 #include "lstate.h"
  35 #include "ltable.h"
  36
  37
  38 /*
  39 ** max size of array part is 2^MAXBITS
  40 */
  41 #if LUAI_BITSINT > 26
  42 #define MAXBITS         26
  43 #else
  44 #define MAXBITS         (LUAI_BITSINT-2)
  45 #endif
  46
  47 #define MAXASIZE        (1 << MAXBITS)
  48
  49
  50 #define hashpow2(t,n)      (gnode(t, lmod((n), sizenode(t))))
  51
  52 #define hashstr(t,str)  hashpow2(t, (str)->tsv.hash)
  53 #define hashboolean(t,p)        hashpow2(t, p)
  54
  55
  56 /*
  57 ** for some types, it is better to avoid modulus by power of 2, as
  58 ** they tend to have many 2 factors.
  59 */
  60 #define hashmod(t,n)    (gnode(t, ((n) % ((sizenode(t)-1)|1))))
  61
  62
  63 #define hashpointer(t,p)        hashmod(t, IntPoint(p))
  64
  65
  66 /*
  67 ** number of ints inside a lua_Number
  68 */
  69 #define numints         cast_int(sizeof(lua_Number)/sizeof(int))
  70
  71
  72
  73 #define dummynode               (&dummynode_)
  74
  75 static const Node dummynode_ = {
  76   {{NULL}, LUA_TNIL},  /* value */
  77   {{{NULL}, LUA_TNIL, NULL}}  /* key */
  78 };
  79
  80
  81 /*
  82 ** hash for lua_Numbers
  83 */
  84 static Node *hashnum (const Table *t, lua_Number n) {
  85   unsigned int a[numints];
  86   int i;
  87   if (luai_numeq(n, 0))  /* avoid problems with -0 */
  88     return gnode(t, 0);
  89   memcpy(a, &n, sizeof(a));
  90   for (i = 1; i < numints; i++) a[0] += a[i];
  91   return hashmod(t, a[0]);
  92 }
  93
  94
  95
  96 /*
  97 ** returns the `main' position of an element in a table (that is, the index
  98 ** of its hash value)
  99 */
 100 static Node *mainposition (const Table *t, const TValue *key) {
 101   switch (ttype(key)) {
 102     case LUA_TNUMBER:
 103       return hashnum(t, nvalue(key));
 104     case LUA_TSTRING:
 105       return hashstr(t, rawtsvalue(key));
 106     case LUA_TBOOLEAN:
 107       return hashboolean(t, bvalue(key));
 108     case LUA_TLIGHTUSERDATA:
 109       return hashpointer(t, pvalue(key));
 110     default:
 111       return hashpointer(t, gcvalue(key));
 112   }
 113 }
 114
 115
 116 /*
 117 ** returns the index for `key' if `key' is an appropriate key to live in
 118 ** the array part of the table, -1 otherwise.
 119 */
 120 static int arrayindex (const TValue *key) {
 121   if (ttisnumber(key)) {
 122     lua_Number n = nvalue(key);
 123     int k;
 124     lua_number2int(k, n);
 125     if (luai_numeq(cast_num(k), n))
 126       return k;
 127   }
 128   return -1;  /* `key' did not match some condition */
 129 }
 130
 131
 132 /*
 133 ** returns the index of a `key' for table traversals. First goes all
 134 ** elements in the array part, then elements in the hash part. The
 135 ** beginning of a traversal is signalled by -1.
 136 */
 137 static int findindex (lua_State *L, Table *t, StkId key) {
 138   int i;
 139   if (ttisnil(key)) return -1;  /* first iteration */
 140   i = arrayindex(key);
 141   if (0 < i && i <= t->sizearray)  /* is `key' inside array part? */
 142     return i-1;  /* yes; that's the index (corrected to C) */
 143   else {
 144     Node *n = mainposition(t, key);
 145     do {  /* check whether `key' is somewhere in the chain */
 146       /* key may be dead already, but it is ok to use it in `next' */
 147       if (luaO_rawequalObj(key2tval(n), key) ||
 148             (ttype(gkey(n)) == LUA_TDEADKEY && iscollectable(key) &&
 149              gcvalue(gkey(n)) == gcvalue(key))) {
 150         i = cast_int(n - gnode(t, 0));  /* key index in hash table */
 151         /* hash elements are numbered after array ones */
 152         return i + t->sizearray;
 153       }
 154       else n = gnext(n);
 155     } while (n);
 156     luaG_runerror(L, "invalid key to " LUA_QL("next"));  /* key not found */
 157     return 0;  /* to avoid warnings */
 158   }
 159 }
 160
 161
 162 int luaH_next (lua_State *L, Table *t, StkId key) {
 163   int i = findindex(L, t, key);  /* find original element */
 164   for (i++; i < t->sizearray; i++) {  /* try first array part */
 165     if (!ttisnil(&t->array[i])) {  /* a non-nil value? */
 166       setnvalue(key, cast_num(i+1));
 167       setobj2s(L, key+1, &t->array[i]);
 168       return 1;
 169     }
 170   }
 171   for (i -= t->sizearray; i < sizenode(t); i++) {  /* then hash part */
 172     if (!ttisnil(gval(gnode(t, i)))) {  /* a non-nil value? */
 173       setobj2s(L, key, key2tval(gnode(t, i)));
 174       setobj2s(L, key+1, gval(gnode(t, i)));
 175       return 1;
 176     }
 177   }
 178   return 0;  /* no more elements */
 179 }
 180
 181
 182 /*
 183 ** {=============================================================
 184 ** Rehash
 185 ** ==============================================================
 186 */
 187
 188
 189 static int computesizes (int nums[], int *narray) {
 190   int i;
 191   int twotoi;  /* 2^i */
 192   int a = 0;  /* number of elements smaller than 2^i */
 193   int na = 0;  /* number of elements to go to array part */
 194   int n = 0;  /* optimal size for array part */
 195   for (i = 0, twotoi = 1; twotoi/2 < *narray; i++, twotoi *= 2) {
 196     if (nums[i] > 0) {
 197       a += nums[i];
 198       if (a > twotoi/2) {  /* more than half elements present? */
 199         n = twotoi;  /* optimal size (till now) */
 200         na = a;  /* all elements smaller than n will go to array part */
 201       }
 202     }
 203     if (a == *narray) break;  /* all elements already counted */
 204   }
 205   *narray = n;
 206   lua_assert(*narray/2 <= na && na <= *narray);
 207   return na;
 208 }
 209
 210
 211 static int countint (const TValue *key, int *nums) {
 212   int k = arrayindex(key);
 213   if (0 < k && k <= MAXASIZE) {  /* is `key' an appropriate array index? */
 214     nums[ceillog2(k)]++;  /* count as such */
 215     return 1;
 216   }
 217   else
 218     return 0;
 219 }
 220
 221
 222 static int numusearray (const Table *t, int *nums) {
 223   int lg;
 224   int ttlg;  /* 2^lg */
 225   int ause = 0;  /* summation of `nums' */
 226   int i = 1;  /* count to traverse all array keys */
 227   for (lg=0, ttlg=1; lg<=MAXBITS; lg++, ttlg*=2) {  /* for each slice */
 228     int lc = 0;  /* counter */
 229     int lim = ttlg;
 230     if (lim > t->sizearray) {
 231       lim = t->sizearray;  /* adjust upper limit */
 232       if (i > lim)
 233         break;  /* no more elements to count */
 234     }
 235     /* count elements in range (2^(lg-1), 2^lg] */
 236     for (; i <= lim; i++) {
 237       if (!ttisnil(&t->array[i-1]))
 238         lc++;
 239     }
 240     nums[lg] += lc;
 241     ause += lc;
 242   }
 243   return ause;
 244 }
 245
 246
 247 static int numusehash (const Table *t, int *nums, int *pnasize) {
 248   int totaluse = 0;  /* total number of elements */
 249   int ause = 0;  /* summation of `nums' */
 250   int i = sizenode(t);
 251   while (i--) {
 252     Node *n = &t->node[i];
 253     if (!ttisnil(gval(n))) {
 254       ause += countint(key2tval(n), nums);
 255       totaluse++;
 256     }
 257   }
 258   *pnasize += ause;
 259   return totaluse;
 260 }
 261
 262
 263 static void setarrayvector (lua_State *L, Table *t, int size) {
 264   int i;
 265   luaM_reallocvector(L, t->array, t->sizearray, size, TValue);
 266   for (i=t->sizearray; i<size; i++)
 267      setnilvalue(&t->array[i]);
 268   t->sizearray = size;
 269 }
 270
 271
 272 static void setnodevector (lua_State *L, Table *t, int size) {
 273   int lsize;
 274   if (size == 0) {  /* no elements to hash part? */
 275     t->node = cast(Node *, dummynode);  /* use common `dummynode' */
 276     lsize = 0;
 277   }
 278   else {
 279     int i;
 280     lsize = ceillog2(size);
 281     if (lsize > MAXBITS)
 282       luaG_runerror(L, "table overflow");
 283     size = twoto(lsize);
 284     t->node = luaM_newvector(L, size, Node);
 285     for (i=0; i<size; i++) {
 286       Node *n = gnode(t, i);
 287       gnext(n) = NULL;
 288       setnilvalue(gkey(n));
 289       setnilvalue(gval(n));
 290     }
 291   }
 292   t->lsizenode = cast_byte(lsize);
 293   t->lastfree = gnode(t, size);  /* all positions are free */
 294 }
 295
 296
 297 static void resize (lua_State *L, Table *t, int nasize, int nhsize) {
 298   int i;
 299   int oldasize = t->sizearray;
 300   int oldhsize = t->lsizenode;
 301   Node *nold = t->node;  /* save old hash ... */
 302   if (nasize > oldasize)  /* array part must grow? */
 303     setarrayvector(L, t, nasize);
 304   /* create new hash part with appropriate size */
 305   setnodevector(L, t, nhsize);
 306   if (nasize < oldasize) {  /* array part must shrink? */
 307     t->sizearray = nasize;
 308     /* re-insert elements from vanishing slice */
 309     for (i=nasize; i<oldasize; i++) {
 310       if (!ttisnil(&t->array[i]))
 311         setobjt2t(L, luaH_setnum(L, t, i+1), &t->array[i]);
 312     }
 313     /* shrink array */
 314     luaM_reallocvector(L, t->array, oldasize, nasize, TValue);
 315   }
 316   /* re-insert elements from hash part */
 317   for (i = twoto(oldhsize) - 1; i >= 0; i--) {
 318     Node *old = nold+i;
 319     if (!ttisnil(gval(old)))
 320       setobjt2t(L, luaH_set(L, t, key2tval(old)), gval(old));
 321   }
 322   if (nold != dummynode)
 323     luaM_freearray(L, nold, twoto(oldhsize), Node);  /* free old array */
 324 }
 325
 326
 327 void luaH_resizearray (lua_State *L, Table *t, int nasize) {
 328   int nsize = (t->node == dummynode) ? 0 : sizenode(t);
 329   resize(L, t, nasize, nsize);
 330 }
 331
 332
 333 static void rehash (lua_State *L, Table *t, const TValue *ek) {
 334   int nasize, na;
 335   int nums[MAXBITS+1];  /* nums[i] = number of keys between 2^(i-1) and 2^i */
 336   int i;
 337   int totaluse;
 338   for (i=0; i<=MAXBITS; i++) nums[i] = 0;  /* reset counts */
 339   nasize = numusearray(t, nums);  /* count keys in array part */
 340   totaluse = nasize;  /* all those keys are integer keys */
 341   totaluse += numusehash(t, nums, &nasize);  /* count keys in hash part */
 342   /* count extra key */
 343   nasize += countint(ek, nums);
 344   totaluse++;
 345   /* compute new size for array part */
 346   na = computesizes(nums, &nasize);
 347   /* resize the table to new computed sizes */
 348   resize(L, t, nasize, totaluse - na);
 349 }
 350
 351
 352
 353 /*
 354 ** }=============================================================
 355 */
 356
 357
 358 Table *luaH_new (lua_State *L, int narray, int nhash) {
 359   Table *t = luaM_new(L, Table);
 360   luaC_link(L, obj2gco(t), LUA_TTABLE);
 361   t->metatable = NULL;
 362   t->flags = cast_byte(~0);
 363   /* temporary values (kept only if some malloc fails) */
 364   t->array = NULL;
 365   t->sizearray = 0;
 366   t->lsizenode = 0;
 367   t->node = cast(Node *, dummynode);
 368   setarrayvector(L, t, narray);
 369   setnodevector(L, t, nhash);
 370   return t;
 371 }
 372
 373
 374 void luaH_free (lua_State *L, Table *t) {
 375   if (t->node != dummynode)
 376     luaM_freearray(L, t->node, sizenode(t), Node);
 377   luaM_freearray(L, t->array, t->sizearray, TValue);
 378   luaM_free(L, t);
 379 }
 380
 381
 382 static Node *getfreepos (Table *t) {
 383   while (t->lastfree-- > t->node) {
 384     if (ttisnil(gkey(t->lastfree)))
 385       return t->lastfree;
 386   }
 387   return NULL;  /* could not find a free place */
 388 }
 389
 390
 391
 392 /*
 393 ** inserts a new key into a hash table; first, check whether key's main
 394 ** position is free. If not, check whether colliding node is in its main
 395 ** position or not: if it is not, move colliding node to an empty place and
 396 ** put new key in its main position; otherwise (colliding node is in its main
 397 ** position), new key goes to an empty position.
 398 */
 399 static TValue *newkey (lua_State *L, Table *t, const TValue *key) {
 400   Node *mp = mainposition(t, key);
 401   if (!ttisnil(gval(mp)) || mp == dummynode) {
 402     Node *othern;
 403     Node *n = getfreepos(t);  /* get a free place */
 404     if (n == NULL) {  /* cannot find a free place? */
 405       rehash(L, t, key);  /* grow table */
 406       return luaH_set(L, t, key);  /* re-insert key into grown table */
 407     }
 408     lua_assert(n != dummynode);
 409     othern = mainposition(t, key2tval(mp));
 410     if (othern != mp) {  /* is colliding node out of its main position? */
 411       /* yes; move colliding node into free position */
 412       while (gnext(othern) != mp) othern = gnext(othern);  /* find previous */
 413       gnext(othern) = n;  /* redo the chain with `n' in place of `mp' */
 414       *n = *mp;  /* copy colliding node into free pos. (mp->next also goes) */
 415       gnext(mp) = NULL;  /* now `mp' is free */
 416       setnilvalue(gval(mp));
 417     }
 418     else {  /* colliding node is in its own main position */
 419       /* new node will go into free position */
 420       gnext(n) = gnext(mp);  /* chain new position */
 421       gnext(mp) = n;
 422       mp = n;
 423     }
 424   }
 425   gkey(mp)->value = key->value; gkey(mp)->tt = key->tt;
 426   luaC_barriert(L, t, key);
 427   lua_assert(ttisnil(gval(mp)));
 428   return gval(mp);
 429 }
 430
 431
 432 /*
 433 ** search function for integers
 434 */
 435 const TValue *luaH_getnum (Table *t, int key) {
 436   /* (1 <= key && key <= t->sizearray) */
 437   if (cast(unsigned int, key-1) < cast(unsigned int, t->sizearray))
 438     return &t->array[key-1];
 439   else {
 440     lua_Number nk = cast_num(key);
 441     Node *n = hashnum(t, nk);
 442     do {  /* check whether `key' is somewhere in the chain */
 443       if (ttisnumber(gkey(n)) && luai_numeq(nvalue(gkey(n)), nk))
 444         return gval(n);  /* that's it */
 445       else n = gnext(n);
 446     } while (n);
 447     return luaO_nilobject;
 448   }
 449 }
 450
 451
 452 /*
 453 ** search function for strings
 454 */
 455 const TValue *luaH_getstr (Table *t, TString *key) {
 456   Node *n = hashstr(t, key);
 457   do {  /* check whether `key' is somewhere in the chain */
 458     if (ttisstring(gkey(n)) && rawtsvalue(gkey(n)) == key)
 459       return gval(n);  /* that's it */
 460     else n = gnext(n);
 461   } while (n);
 462   return luaO_nilobject;
 463 }
 464
 465
 466 /*
 467 ** main search function
 468 */
 469 const TValue *luaH_get (Table *t, const TValue *key) {
 470   switch (ttype(key)) {
 471     case LUA_TNIL: return luaO_nilobject;
 472     case LUA_TSTRING: return luaH_getstr(t, rawtsvalue(key));
 473     case LUA_TNUMBER: {
 474       int k;
 475       lua_Number n = nvalue(key);
 476       lua_number2int(k, n);
 477       if (luai_numeq(cast_num(k), nvalue(key))) /* index is int? */
 478         return luaH_getnum(t, k);  /* use specialized version */
 479       /* else go through */
 480     }
 481     default: {
 482       Node *n = mainposition(t, key);
 483       do {  /* check whether `key' is somewhere in the chain */
 484         if (luaO_rawequalObj(key2tval(n), key))
 485           return gval(n);  /* that's it */
 486         else n = gnext(n);
 487       } while (n);
 488       return luaO_nilobject;
 489     }
 490   }
 491 }
 492
 493
 494 TValue *luaH_set (lua_State *L, Table *t, const TValue *key) {
 495   const TValue *p = luaH_get(t, key);
 496   t->flags = 0;
 497   if (p != luaO_nilobject)
 498     return cast(TValue *, p);
 499   else {
 500     if (ttisnil(key)) luaG_runerror(L, "table index is nil");
 501     else if (ttisnumber(key) && luai_numisnan(nvalue(key)))
 502       luaG_runerror(L, "table index is NaN");
 503     return newkey(L, t, key);
 504   }
 505 }
 506
 507
 508 TValue *luaH_setnum (lua_State *L, Table *t, int key) {
 509   const TValue *p = luaH_getnum(t, key);
 510   if (p != luaO_nilobject)
 511     return cast(TValue *, p);
 512   else {
 513     TValue k;
 514     setnvalue(&k, cast_num(key));
 515     return newkey(L, t, &k);
 516   }
 517 }
 518
 519
 520 TValue *luaH_setstr (lua_State *L, Table *t, TString *key) {
 521   const TValue *p = luaH_getstr(t, key);
 522   if (p != luaO_nilobject)
 523     return cast(TValue *, p);
 524   else {
 525     TValue k;
 526     setsvalue(L, &k, key);
 527     return newkey(L, t, &k);
 528   }
 529 }
 530
 531
 532 static int unbound_search (Table *t, unsigned int j) {
 533   unsigned int i = j;  /* i is zero or a present index */
 534   j++;
 535   /* find `i' and `j' such that i is present and j is not */
 536   while (!ttisnil(luaH_getnum(t, j))) {
 537     i = j;
 538     j *= 2;
 539     if (j > cast(unsigned int, MAX_INT)) {  /* overflow? */
 540       /* table was built with bad purposes: resort to linear search */
 541       i = 1;
 542       while (!ttisnil(luaH_getnum(t, i))) i++;
 543       return i - 1;
 544     }
 545   }
 546   /* now do a binary search between them */
 547   while (j - i > 1) {
 548     unsigned int m = (i+j)/2;
 549     if (ttisnil(luaH_getnum(t, m))) j = m;
 550     else i = m;
 551   }
 552   return i;
 553 }
 554
 555
 556 /*
 557 ** Try to find a boundary in table `t'. A `boundary' is an integer index
 558 ** such that t[i] is non-nil and t[i+1] is nil (and 0 if t[1] is nil).
 559 */
 560 int luaH_getn (Table *t) {
 561   unsigned int j = t->sizearray;
 562   if (j > 0 && ttisnil(&t->array[j - 1])) {
 563     /* there is a boundary in the array part: (binary) search for it */
 564     unsigned int i = 0;
 565     while (j - i > 1) {
 566       unsigned int m = (i+j)/2;
 567       if (ttisnil(&t->array[m - 1])) j = m;
 568       else i = m;
 569     }
 570     return i;
 571   }
 572   /* else must find a boundary in hash part */
 573   else if (t->node == dummynode)  /* hash part is empty? */
 574     return j;  /* that is easy... */
 575   else return unbound_search(t, j);
 576 }
 577
 578
 579
 580 #if defined(LUA_DEBUG)
 581
 582 Node *luaH_mainposition (const Table *t, const TValue *key) {
 583   return mainposition(t, key);
 584 }
 585
 586 int luaH_isdummy (Node *n) { return n == dummynode; }
 587
 588 #endif