liblua/ltable.c

   1 /*
   2 ** $Id: ltable.c,v 2.72 2012/09/11 19:37:16 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 <string.h>
  22
  23 #define ltable_c
  24 #define LUA_CORE
  25
  26 #include "lua.h"
  27
  28 #include "ldebug.h"
  29 #include "ldo.h"
  30 #include "lgc.h"
  31 #include "lmem.h"
  32 #include "lobject.h"
  33 #include "lstate.h"
  34 #include "lstring.h"
  35 #include "ltable.h"
  36 #include "lvm.h"
  37
  38
  39 /*
  40 ** max size of array part is 2^MAXBITS
  41 */
  42 #if LUAI_BITSINT >= 32
  43 #define MAXBITS         30
  44 #else
  45 #define MAXBITS         (LUAI_BITSINT-2)
  46 #endif
  47
  48 #define MAXASIZE        (1 << MAXBITS)
  49
  50
  51 #define hashpow2(t,n)           (gnode(t, lmod((n), sizenode(t))))
  52
  53 #define hashstr(t,str)          hashpow2(t, (str)->tsv.hash)
  54 #define hashboolean(t,p)        hashpow2(t, p)
  55
  56
  57 /*
  58 ** for some types, it is better to avoid modulus by power of 2, as
  59 ** they tend to have many 2 factors.
  60 */
  61 #define hashmod(t,n)    (gnode(t, ((n) % ((sizenode(t)-1)|1))))
  62
  63
  64 #define hashpointer(t,p)        hashmod(t, IntPoint(p))
  65
  66
  67 #define dummynode               (&dummynode_)
  68
  69 #define isdummy(n)              ((n) == dummynode)
  70
  71 static const Node dummynode_ = {
  72   {NILCONSTANT},  /* value */
  73   {{NILCONSTANT, NULL}}  /* key */
  74 };
  75
  76
  77 /*
  78 ** hash for lua_Numbers
  79 */
  80 static Node *hashnum (const Table *t, lua_Number n) {
  81   int i;
  82   luai_hashnum(i, n);
  83   if (i < 0) {
  84     if (cast(unsigned int, i) == 0u - i)  /* use unsigned to avoid overflows */
  85       i = 0;  /* handle INT_MIN */
  86     i = -i;  /* must be a positive value */
  87   }
  88   return hashmod(t, i);
  89 }
  90
  91
  92
  93 /*
  94 ** returns the `main' position of an element in a table (that is, the index
  95 ** of its hash value)
  96 */
  97 static Node *mainposition (const Table *t, const TValue *key) {
  98   switch (ttype(key)) {
  99     case LUA_TNUMBER:
 100       return hashnum(t, nvalue(key));
 101     case LUA_TLNGSTR: {
 102       TString *s = rawtsvalue(key);
 103       if (s->tsv.extra == 0) {  /* no hash? */
 104         s->tsv.hash = luaS_hash(getstr(s), s->tsv.len, s->tsv.hash);
 105         s->tsv.extra = 1;  /* now it has its hash */
 106       }
 107       return hashstr(t, rawtsvalue(key));
 108     }
 109     case LUA_TSHRSTR:
 110       return hashstr(t, rawtsvalue(key));
 111     case LUA_TBOOLEAN:
 112       return hashboolean(t, bvalue(key));
 113     case LUA_TLIGHTUSERDATA:
 114       return hashpointer(t, pvalue(key));
 115     case LUA_TLCF:
 116       return hashpointer(t, fvalue(key));
 117     default:
 118       return hashpointer(t, gcvalue(key));
 119   }
 120 }
 121
 122
 123 /*
 124 ** returns the index for `key' if `key' is an appropriate key to live in
 125 ** the array part of the table, -1 otherwise.
 126 */
 127 static int arrayindex (const TValue *key) {
 128   if (ttisnumber(key)) {
 129     lua_Number n = nvalue(key);
 130     int k;
 131     lua_number2int(k, n);
 132     if (luai_numeq(cast_num(k), n))
 133       return k;
 134   }
 135   return -1;  /* `key' did not match some condition */
 136 }
 137
 138
 139 /*
 140 ** returns the index of a `key' for table traversals. First goes all
 141 ** elements in the array part, then elements in the hash part. The
 142 ** beginning of a traversal is signaled by -1.
 143 */
 144 static int findindex (lua_State *L, Table *t, StkId key) {
 145   int i;
 146   if (ttisnil(key)) return -1;  /* first iteration */
 147   i = arrayindex(key);
 148   if (0 < i && i <= t->sizearray)  /* is `key' inside array part? */
 149     return i-1;  /* yes; that's the index (corrected to C) */
 150   else {
 151     Node *n = mainposition(t, key);
 152     for (;;) {  /* check whether `key' is somewhere in the chain */
 153       /* key may be dead already, but it is ok to use it in `next' */
 154       if (luaV_rawequalobj(gkey(n), key) ||
 155             (ttisdeadkey(gkey(n)) && iscollectable(key) &&
 156              deadvalue(gkey(n)) == gcvalue(key))) {
 157         i = cast_int(n - gnode(t, 0));  /* key index in hash table */
 158         /* hash elements are numbered after array ones */
 159         return i + t->sizearray;
 160       }
 161       else n = gnext(n);
 162       if (n == NULL)
 163         luaG_runerror(L, "invalid key to " LUA_QL("next"));  /* key not found */
 164     }
 165   }
 166 }
 167
 168
 169 int luaH_next (lua_State *L, Table *t, StkId key) {
 170   int i = findindex(L, t, key);  /* find original element */
 171   for (i++; i < t->sizearray; i++) {  /* try first array part */
 172     if (!ttisnil(&t->array[i])) {  /* a non-nil value? */
 173       setnvalue(key, cast_num(i+1));
 174       setobj2s(L, key+1, &t->array[i]);
 175       return 1;
 176     }
 177   }
 178   for (i -= t->sizearray; i < sizenode(t); i++) {  /* then hash part */
 179     if (!ttisnil(gval(gnode(t, i)))) {  /* a non-nil value? */
 180       setobj2s(L, key, gkey(gnode(t, i)));
 181       setobj2s(L, key+1, gval(gnode(t, i)));
 182       return 1;
 183     }
 184   }
 185   return 0;  /* no more elements */
 186 }
 187
 188
 189 /*
 190 ** {=============================================================
 191 ** Rehash
 192 ** ==============================================================
 193 */
 194
 195
 196 static int computesizes (int nums[], int *narray) {
 197   int i;
 198   int twotoi;  /* 2^i */
 199   int a = 0;  /* number of elements smaller than 2^i */
 200   int na = 0;  /* number of elements to go to array part */
 201   int n = 0;  /* optimal size for array part */
 202   for (i = 0, twotoi = 1; twotoi/2 < *narray; i++, twotoi *= 2) {
 203     if (nums[i] > 0) {
 204       a += nums[i];
 205       if (a > twotoi/2) {  /* more than half elements present? */
 206         n = twotoi;  /* optimal size (till now) */
 207         na = a;  /* all elements smaller than n will go to array part */
 208       }
 209     }
 210     if (a == *narray) break;  /* all elements already counted */
 211   }
 212   *narray = n;
 213   lua_assert(*narray/2 <= na && na <= *narray);
 214   return na;
 215 }
 216
 217
 218 static int countint (const TValue *key, int *nums) {
 219   int k = arrayindex(key);
 220   if (0 < k && k <= MAXASIZE) {  /* is `key' an appropriate array index? */
 221     nums[luaO_ceillog2(k)]++;  /* count as such */
 222     return 1;
 223   }
 224   else
 225     return 0;
 226 }
 227
 228
 229 static int numusearray (const Table *t, int *nums) {
 230   int lg;
 231   int ttlg;  /* 2^lg */
 232   int ause = 0;  /* summation of `nums' */
 233   int i = 1;  /* count to traverse all array keys */
 234   for (lg=0, ttlg=1; lg<=MAXBITS; lg++, ttlg*=2) {  /* for each slice */
 235     int lc = 0;  /* counter */
 236     int lim = ttlg;
 237     if (lim > t->sizearray) {
 238       lim = t->sizearray;  /* adjust upper limit */
 239       if (i > lim)
 240         break;  /* no more elements to count */
 241     }
 242     /* count elements in range (2^(lg-1), 2^lg] */
 243     for (; i <= lim; i++) {
 244       if (!ttisnil(&t->array[i-1]))
 245         lc++;
 246     }
 247     nums[lg] += lc;
 248     ause += lc;
 249   }
 250   return ause;
 251 }
 252
 253
 254 static int numusehash (const Table *t, int *nums, int *pnasize) {
 255   int totaluse = 0;  /* total number of elements */
 256   int ause = 0;  /* summation of `nums' */
 257   int i = sizenode(t);
 258   while (i--) {
 259     Node *n = &t->node[i];
 260     if (!ttisnil(gval(n))) {
 261       ause += countint(gkey(n), nums);
 262       totaluse++;
 263     }
 264   }
 265   *pnasize += ause;
 266   return totaluse;
 267 }
 268
 269
 270 static void setarrayvector (lua_State *L, Table *t, int size) {
 271   int i;
 272   luaM_reallocvector(L, t->array, t->sizearray, size, TValue);
 273   for (i=t->sizearray; i<size; i++)
 274      setnilvalue(&t->array[i]);
 275   t->sizearray = size;
 276 }
 277
 278
 279 static void setnodevector (lua_State *L, Table *t, int size) {
 280   int lsize;
 281   if (size == 0) {  /* no elements to hash part? */
 282     t->node = cast(Node *, dummynode);  /* use common `dummynode' */
 283     lsize = 0;
 284   }
 285   else {
 286     int i;
 287     lsize = luaO_ceillog2(size);
 288     if (lsize > MAXBITS)
 289       luaG_runerror(L, "table overflow");
 290     size = twoto(lsize);
 291     t->node = luaM_newvector(L, size, Node);
 292     for (i=0; i<size; i++) {
 293       Node *n = gnode(t, i);
 294       gnext(n) = NULL;
 295       setnilvalue(gkey(n));
 296       setnilvalue(gval(n));
 297     }
 298   }
 299   t->lsizenode = cast_byte(lsize);
 300   t->lastfree = gnode(t, size);  /* all positions are free */
 301 }
 302
 303
 304 void luaH_resize (lua_State *L, Table *t, int nasize, int nhsize) {
 305   int i;
 306   int oldasize = t->sizearray;
 307   int oldhsize = t->lsizenode;
 308   Node *nold = t->node;  /* save old hash ... */
 309   if (nasize > oldasize)  /* array part must grow? */
 310     setarrayvector(L, t, nasize);
 311   /* create new hash part with appropriate size */
 312   setnodevector(L, t, nhsize);
 313   if (nasize < oldasize) {  /* array part must shrink? */
 314     t->sizearray = nasize;
 315     /* re-insert elements from vanishing slice */
 316     for (i=nasize; i<oldasize; i++) {
 317       if (!ttisnil(&t->array[i]))
 318         luaH_setint(L, t, i + 1, &t->array[i]);
 319     }
 320     /* shrink array */
 321     luaM_reallocvector(L, t->array, oldasize, nasize, TValue);
 322   }
 323   /* re-insert elements from hash part */
 324   for (i = twoto(oldhsize) - 1; i >= 0; i--) {
 325     Node *old = nold+i;
 326     if (!ttisnil(gval(old))) {
 327       /* doesn't need barrier/invalidate cache, as entry was
 328          already present in the table */
 329       setobjt2t(L, luaH_set(L, t, gkey(old)), gval(old));
 330     }
 331   }
 332   if (!isdummy(nold))
 333     luaM_freearray(L, nold, cast(size_t, twoto(oldhsize))); /* free old array */
 334 }
 335
 336
 337 void luaH_resizearray (lua_State *L, Table *t, int nasize) {
 338   int nsize = isdummy(t->node) ? 0 : sizenode(t);
 339   luaH_resize(L, t, nasize, nsize);
 340 }
 341
 342
 343 static void rehash (lua_State *L, Table *t, const TValue *ek) {
 344   int nasize, na;
 345   int nums[MAXBITS+1];  /* nums[i] = number of keys with 2^(i-1) < k <= 2^i */
 346   int i;
 347   int totaluse;
 348   for (i=0; i<=MAXBITS; i++) nums[i] = 0;  /* reset counts */
 349   nasize = numusearray(t, nums);  /* count keys in array part */
 350   totaluse = nasize;  /* all those keys are integer keys */
 351   totaluse += numusehash(t, nums, &nasize);  /* count keys in hash part */
 352   /* count extra key */
 353   nasize += countint(ek, nums);
 354   totaluse++;
 355   /* compute new size for array part */
 356   na = computesizes(nums, &nasize);
 357   /* resize the table to new computed sizes */
 358   luaH_resize(L, t, nasize, totaluse - na);
 359 }
 360
 361
 362
 363 /*
 364 ** }=============================================================
 365 */
 366
 367
 368 Table *luaH_new (lua_State *L) {
 369   Table *t = &luaC_newobj(L, LUA_TTABLE, sizeof(Table), NULL, 0)->h;
 370   t->metatable = NULL;
 371   t->flags = cast_byte(~0);
 372   t->array = NULL;
 373   t->sizearray = 0;
 374   setnodevector(L, t, 0);
 375   return t;
 376 }
 377
 378
 379 void luaH_free (lua_State *L, Table *t) {
 380   if (!isdummy(t->node))
 381     luaM_freearray(L, t->node, cast(size_t, sizenode(t)));
 382   luaM_freearray(L, t->array, t->sizearray);
 383   luaM_free(L, t);
 384 }
 385
 386
 387 static Node *getfreepos (Table *t) {
 388   while (t->lastfree > t->node) {
 389     t->lastfree--;
 390     if (ttisnil(gkey(t->lastfree)))
 391       return t->lastfree;
 392   }
 393   return NULL;  /* could not find a free place */
 394 }
 395
 396
 397
 398 /*
 399 ** inserts a new key into a hash table; first, check whether key's main
 400 ** position is free. If not, check whether colliding node is in its main
 401 ** position or not: if it is not, move colliding node to an empty place and
 402 ** put new key in its main position; otherwise (colliding node is in its main
 403 ** position), new key goes to an empty position.
 404 */
 405 TValue *luaH_newkey (lua_State *L, Table *t, const TValue *key) {
 406   Node *mp;
 407   if (ttisnil(key)) luaG_runerror(L, "table index is nil");
 408   else if (ttisnumber(key) && luai_numisnan(L, nvalue(key)))
 409     luaG_runerror(L, "table index is NaN");
 410   mp = mainposition(t, key);
 411   if (!ttisnil(gval(mp)) || isdummy(mp)) {  /* main position is taken? */
 412     Node *othern;
 413     Node *n = getfreepos(t);  /* get a free place */
 414     if (n == NULL) {  /* cannot find a free place? */
 415       rehash(L, t, key);  /* grow table */
 416       /* whatever called 'newkey' take care of TM cache and GC barrier */
 417       return luaH_set(L, t, key);  /* insert key into grown table */
 418     }
 419     lua_assert(!isdummy(n));
 420     othern = mainposition(t, gkey(mp));
 421     if (othern != mp) {  /* is colliding node out of its main position? */
 422       /* yes; move colliding node into free position */
 423       while (gnext(othern) != mp) othern = gnext(othern);  /* find previous */
 424       gnext(othern) = n;  /* redo the chain with `n' in place of `mp' */
 425       *n = *mp;  /* copy colliding node into free pos. (mp->next also goes) */
 426       gnext(mp) = NULL;  /* now `mp' is free */
 427       setnilvalue(gval(mp));
 428     }
 429     else {  /* colliding node is in its own main position */
 430       /* new node will go into free position */
 431       gnext(n) = gnext(mp);  /* chain new position */
 432       gnext(mp) = n;
 433       mp = n;
 434     }
 435   }
 436   setobj2t(L, gkey(mp), key);
 437   luaC_barrierback(L, obj2gco(t), key);
 438   lua_assert(ttisnil(gval(mp)));
 439   return gval(mp);
 440 }
 441
 442
 443 /*
 444 ** search function for integers
 445 */
 446 const TValue *luaH_getint (Table *t, int key) {
 447   /* (1 <= key && key <= t->sizearray) */
 448   if (cast(unsigned int, key-1) < cast(unsigned int, t->sizearray))
 449     return &t->array[key-1];
 450   else {
 451     lua_Number nk = cast_num(key);
 452     Node *n = hashnum(t, nk);
 453     do {  /* check whether `key' is somewhere in the chain */
 454       if (ttisnumber(gkey(n)) && luai_numeq(nvalue(gkey(n)), nk))
 455         return gval(n);  /* that's it */
 456       else n = gnext(n);
 457     } while (n);
 458     return luaO_nilobject;
 459   }
 460 }
 461
 462
 463 /*
 464 ** search function for short strings
 465 */
 466 const TValue *luaH_getstr (Table *t, TString *key) {
 467   Node *n = hashstr(t, key);
 468   lua_assert(key->tsv.tt == LUA_TSHRSTR);
 469   do {  /* check whether `key' is somewhere in the chain */
 470     if (ttisshrstring(gkey(n)) && eqshrstr(rawtsvalue(gkey(n)), key))
 471       return gval(n);  /* that's it */
 472     else n = gnext(n);
 473   } while (n);
 474   return luaO_nilobject;
 475 }
 476
 477
 478 /*
 479 ** main search function
 480 */
 481 const TValue *luaH_get (Table *t, const TValue *key) {
 482   switch (ttype(key)) {
 483     case LUA_TSHRSTR: return luaH_getstr(t, rawtsvalue(key));
 484     case LUA_TNIL: return luaO_nilobject;
 485     case LUA_TNUMBER: {
 486       int k;
 487       lua_Number n = nvalue(key);
 488       lua_number2int(k, n);
 489       if (luai_numeq(cast_num(k), n)) /* index is int? */
 490         return luaH_getint(t, k);  /* use specialized version */
 491       /* else go through */
 492     }
 493     default: {
 494       Node *n = mainposition(t, key);
 495       do {  /* check whether `key' is somewhere in the chain */
 496         if (luaV_rawequalobj(gkey(n), key))
 497           return gval(n);  /* that's it */
 498         else n = gnext(n);
 499       } while (n);
 500       return luaO_nilobject;
 501     }
 502   }
 503 }
 504
 505
 506 /*
 507 ** beware: when using this function you probably need to check a GC
 508 ** barrier and invalidate the TM cache.
 509 */
 510 TValue *luaH_set (lua_State *L, Table *t, const TValue *key) {
 511   const TValue *p = luaH_get(t, key);
 512   if (p != luaO_nilobject)
 513     return cast(TValue *, p);
 514   else return luaH_newkey(L, t, key);
 515 }
 516
 517
 518 void luaH_setint (lua_State *L, Table *t, int key, TValue *value) {
 519   const TValue *p = luaH_getint(t, key);
 520   TValue *cell;
 521   if (p != luaO_nilobject)
 522     cell = cast(TValue *, p);
 523   else {
 524     TValue k;
 525     setnvalue(&k, cast_num(key));
 526     cell = luaH_newkey(L, t, &k);
 527   }
 528   setobj2t(L, cell, value);
 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_getint(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_getint(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_getint(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 (isdummy(t->node))  /* 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 isdummy(n); }
 587
 588 #endif