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# lua/ltable.c

Go to the documentation of this file.

    00001 /*
    00002 ** $Id: ltable.c,v 1.3 2007/07/15 17:56:11 rse Exp $
    00003 ** Lua tables (hash)
    00004 ** See Copyright Notice in lua.h
    00005 */
    00006
    00007
    00008 /*
    00009 ** Implementation of tables (aka arrays, objects, or hash tables).
    00010 ** Tables keep its elements in two parts: an array part and a hash part.
    00011 ** Non-negative integer keys are all candidates to be kept in the array
    00012 ** part. The actual size of the array is the largest `n' such that at
    00013 ** least half the slots between 0 and n are in use.
    00014 ** Hash uses a mix of chained scatter table with Brent's variation.
    00015 ** A main invariant of these tables is that, if an element is not
    00016 ** in its main position (i.e. the `original' position that its hash gives
    00017 ** to it), then the colliding element is in its own main position.
    00018 ** Hence even when the load factor reaches 100%, performance remains good.
    00019 */
    00020
    00021 #include <math.h>
    00022 #include <string.h>
    00023
    00024 #define ltable_c
    00025 #define LUA_CORE
    00026
    00027 #include "lua.h"
    00028
    00029 #include "ldebug.h"
    00030 #include "ldo.h"
    00031 #include "lgc.h"
    00032 #include "lmem.h"
    00033 #include "lobject.h"
    00034 #include "lstate.h"
    00035 #include "ltable.h"
    00036
    00037
    00038 /*
    00039 ** max size of array part is 2^MAXBITS
    00040 */
    00041 #if LUAI_BITSINT > 26
    00042 #define MAXBITS         26
    00043 #else
    00044 #define MAXBITS         (LUAI_BITSINT-2)
    00045 #endif
    00046
    00047 #define MAXASIZE        (1 << MAXBITS)
    00048
    00049
    00050 #define hashpow2(t,n)      (gnode(t, lmod((n), sizenode(t))))
    00051
    00052 #define hashstr(t,str)  hashpow2(t, (str)->tsv.hash)
    00053 #define hashboolean(t,p)        hashpow2(t, p)
    00054
    00055
    00056 /*
    00057 ** for some types, it is better to avoid modulus by power of 2, as
    00058 ** they tend to have many 2 factors.
    00059 */
    00060 #define hashmod(t,n)    (gnode(t, ((n) % ((sizenode(t)-1)|1))))
    00061
    00062
    00063 #define hashpointer(t,p)        hashmod(t, IntPoint(p))
    00064
    00065
    00066 /*
    00067 ** number of ints inside a lua_Number
    00068 */
    00069 #define numints         cast_int(sizeof(lua_Number)/sizeof(int))
    00070
    00071
    00072
    00073 #define dummynode               (&dummynode_)
    00074
    00075 static const Node dummynode_ = {
    00076   {{NULL}, LUA_TNIL},  /* value */
    00077   {{{NULL}, LUA_TNIL, NULL}}  /* key */
    00078 };
    00079
    00080
    00081 /*
    00082 ** hash for lua_Numbers
    00083 */
    00084 static Node *hashnum (const Table *t, lua_Number n) {
    00085   unsigned int a[numints];
    00086   int i;
    00087   if (luai_numeq(n, 0))  /* avoid problems with -0 */
    00088     return gnode(t, 0);
    00089   memcpy(a, &n, sizeof(a));
    00090   for (i = 1; i < numints; i++) a[0] += a[i];
    00091   return hashmod(t, a[0]);
    00092 }
    00093
    00094
    00095
    00096 /*
    00097 ** returns the `main' position of an element in a table (that is, the index
    00098 ** of its hash value)
    00099 */
    00100 static Node *mainposition (const Table *t, const TValue *key) {
    00101   switch (ttype(key)) {
    00102     case LUA_TNUMBER:
    00103       return hashnum(t, nvalue(key));
    00104     case LUA_TSTRING:
    00105       return hashstr(t, rawtsvalue(key));
    00106     case LUA_TBOOLEAN:
    00107       return hashboolean(t, bvalue(key));
    00108     case LUA_TLIGHTUSERDATA:
    00109       return hashpointer(t, pvalue(key));
    00110     default:
    00111       return hashpointer(t, gcvalue(key));
    00112   }
    00113 }
    00114
    00115
    00116 /*
    00117 ** returns the index for `key' if `key' is an appropriate key to live in
    00118 ** the array part of the table, -1 otherwise.
    00119 */
    00120 static int arrayindex (const TValue *key) {
    00121   if (ttisnumber(key)) {
    00122     lua_Number n = nvalue(key);
    00123     int k;
    00124     lua_number2int(k, n);
    00125     if (luai_numeq(cast_num(k), n))
    00126       return k;
    00127   }
    00128   return -1;  /* `key' did not match some condition */
    00129 }
    00130
    00131
    00132 /*
    00133 ** returns the index of a `key' for table traversals. First goes all
    00134 ** elements in the array part, then elements in the hash part. The
    00135 ** beginning of a traversal is signalled by -1.
    00136 */
    00137 static int findindex (lua_State *L, Table *t, StkId key) {
    00138   int i;
    00139   if (ttisnil(key)) return -1;  /* first iteration */
    00140   i = arrayindex(key);
    00141   if (0 < i && i <= t->sizearray)  /* is `key' inside array part? */
    00142     return i-1;  /* yes; that's the index (corrected to C) */
    00143   else {
    00144     Node *n = mainposition(t, key);
    00145     do {  /* check whether `key' is somewhere in the chain */
    00146       /* key may be dead already, but it is ok to use it in `next' */
    00147       if (luaO_rawequalObj(key2tval(n), key) ||
    00148             (ttype(gkey(n)) == LUA_TDEADKEY && iscollectable(key) &&
    00149              gcvalue(gkey(n)) == gcvalue(key))) {
    00150         i = cast_int(n - gnode(t, 0));  /* key index in hash table */
    00151         /* hash elements are numbered after array ones */
    00152         return i + t->sizearray;
    00153       }
    00154       else n = gnext(n);
    00155     } while (n);
    00156     luaG_runerror(L, "invalid key to " LUA_QL("next"));  /* key not found */
    00157     return 0;  /* to avoid warnings */
    00158   }
    00159 }
    00160
    00161
    00162 int luaH_next (lua_State *L, Table *t, StkId key) {
    00163   int i = findindex(L, t, key);  /* find original element */
    00164   for (i++; i < t->sizearray; i++) {  /* try first array part */
    00165     if (!ttisnil(&t->array[i])) {  /* a non-nil value? */
    00166       setnvalue(key, cast_num(i+1));
    00167       setobj2s(L, key+1, &t->array[i]);
    00168       return 1;
    00169     }
    00170   }
    00171   for (i -= t->sizearray; i < sizenode(t); i++) {  /* then hash part */
    00172     if (!ttisnil(gval(gnode(t, i)))) {  /* a non-nil value? */
    00173       setobj2s(L, key, key2tval(gnode(t, i)));
    00174       setobj2s(L, key+1, gval(gnode(t, i)));
    00175       return 1;
    00176     }
    00177   }
    00178   return 0;  /* no more elements */
    00179 }
    00180
    00181
    00182 /*
    00183 ** {=============================================================
    00184 ** Rehash
    00185 ** ==============================================================
    00186 */
    00187
    00188
    00189 static int computesizes (int nums[], int *narray) {
    00190   int i;
    00191   int twotoi;  /* 2^i */
    00192   int a = 0;  /* number of elements smaller than 2^i */
    00193   int na = 0;  /* number of elements to go to array part */
    00194   int n = 0;  /* optimal size for array part */
    00195   for (i = 0, twotoi = 1; twotoi/2 < *narray; i++, twotoi *= 2) {
    00196     if (nums[i] > 0) {
    00197       a += nums[i];
    00198       if (a > twotoi/2) {  /* more than half elements present? */
    00199         n = twotoi;  /* optimal size (till now) */
    00200         na = a;  /* all elements smaller than n will go to array part */
    00201       }
    00202     }
    00203     if (a == *narray) break;  /* all elements already counted */
    00204   }
    00205   *narray = n;
    00206   lua_assert(*narray/2 <= na && na <= *narray);
    00207   return na;
    00208 }
    00209
    00210
    00211 static int countint (const TValue *key, int *nums) {
    00212   int k = arrayindex(key);
    00213   if (0 < k && k <= MAXASIZE) {  /* is `key' an appropriate array index? */
    00214     nums[ceillog2(k)]++;  /* count as such */
    00215     return 1;
    00216   }
    00217   else
    00218     return 0;
    00219 }
    00220
    00221
    00222 static int numusearray (const Table *t, int *nums) {
    00223   int lg;
    00224   int ttlg;  /* 2^lg */
    00225   int ause = 0;  /* summation of `nums' */
    00226   int i = 1;  /* count to traverse all array keys */
    00227   for (lg=0, ttlg=1; lg<=MAXBITS; lg++, ttlg*=2) {  /* for each slice */
    00228     int lc = 0;  /* counter */
    00229     int lim = ttlg;
    00230     if (lim > t->sizearray) {
    00231       lim = t->sizearray;  /* adjust upper limit */
    00232       if (i > lim)
    00233         break;  /* no more elements to count */
    00234     }
    00235     /* count elements in range (2^(lg-1), 2^lg] */
    00236     for (; i <= lim; i++) {
    00237       if (!ttisnil(&t->array[i-1]))
    00238         lc++;
    00239     }
    00240     nums[lg] += lc;
    00241     ause += lc;
    00242   }
    00243   return ause;
    00244 }
    00245
    00246
    00247 static int numusehash (const Table *t, int *nums, int *pnasize) {
    00248   int totaluse = 0;  /* total number of elements */
    00249   int ause = 0;  /* summation of `nums' */
    00250   int i = sizenode(t);
    00251   while (i--) {
    00252     Node *n = &t->node[i];
    00253     if (!ttisnil(gval(n))) {
    00254       ause += countint(key2tval(n), nums);
    00255       totaluse++;
    00256     }
    00257   }
    00258   *pnasize += ause;
    00259   return totaluse;
    00260 }
    00261
    00262
    00263 static void setarrayvector (lua_State *L, Table *t, int size) {
    00264   int i;
    00265   luaM_reallocvector(L, t->array, t->sizearray, size, TValue);
    00266   for (i=t->sizearray; i<size; i++)
    00267      setnilvalue(&t->array[i]);
    00268   t->sizearray = size;
    00269 }
    00270
    00271
    00272 static void setnodevector (lua_State *L, Table *t, int size) {
    00273   int lsize;
    00274   if (size == 0) {  /* no elements to hash part? */
    00275     t->node = cast(Node *, dummynode);  /* use common `dummynode' */
    00276     lsize = 0;
    00277   }
    00278   else {
    00279     int i;
    00280     lsize = ceillog2(size);
    00281     if (lsize > MAXBITS)
    00282       luaG_runerror(L, "table overflow");
    00283     size = twoto(lsize);
    00284     t->node = luaM_newvector(L, size, Node);
    00285     for (i=0; i<size; i++) {
    00286       Node *n = gnode(t, i);
    00287       gnext(n) = NULL;
    00288       setnilvalue(gkey(n));
    00289       setnilvalue(gval(n));
    00290     }
    00291   }
    00292   t->lsizenode = cast_byte(lsize);
    00293   t->lastfree = gnode(t, size);  /* all positions are free */
    00294 }
    00295
    00296
    00297 static void resize (lua_State *L, Table *t, int nasize, int nhsize) {
    00298   int i;
    00299   int oldasize = t->sizearray;
    00300   int oldhsize = t->lsizenode;
    00301   Node *nold = t->node;  /* save old hash ... */
    00302   if (nasize > oldasize)  /* array part must grow? */
    00303     setarrayvector(L, t, nasize);
    00304   /* create new hash part with appropriate size */
    00305   setnodevector(L, t, nhsize);
    00306   if (nasize < oldasize) {  /* array part must shrink? */
    00307     t->sizearray = nasize;
    00308     /* re-insert elements from vanishing slice */
    00309     for (i=nasize; i<oldasize; i++) {
    00310       if (!ttisnil(&t->array[i]))
    00311         setobjt2t(L, luaH_setnum(L, t, i+1), &t->array[i]);
    00312     }
    00313     /* shrink array */
    00314     luaM_reallocvector(L, t->array, oldasize, nasize, TValue);
    00315   }
    00316   /* re-insert elements from hash part */
    00317   for (i = twoto(oldhsize) - 1; i >= 0; i--) {
    00318     Node *old = nold+i;
    00319     if (!ttisnil(gval(old)))
    00320       setobjt2t(L, luaH_set(L, t, key2tval(old)), gval(old));
    00321   }
    00322   if (nold != dummynode)
    00323     luaM_freearray(L, nold, twoto(oldhsize), Node);  /* free old array */
    00324 }
    00325
    00326
    00327 void luaH_resizearray (lua_State *L, Table *t, int nasize) {
    00328   int nsize = (t->node == dummynode) ? 0 : sizenode(t);
    00329   resize(L, t, nasize, nsize);
    00330 }
    00331
    00332
    00333 static void rehash (lua_State *L, Table *t, const TValue *ek) {
    00334   int nasize, na;
    00335   int nums[MAXBITS+1];  /* nums[i] = number of keys between 2^(i-1) and 2^i */
    00336   int i;
    00337   int totaluse;
    00338   for (i=0; i<=MAXBITS; i++) nums[i] = 0;  /* reset counts */
    00339   nasize = numusearray(t, nums);  /* count keys in array part */
    00340   totaluse = nasize;  /* all those keys are integer keys */
    00341   totaluse += numusehash(t, nums, &nasize);  /* count keys in hash part */
    00342   /* count extra key */
    00343   nasize += countint(ek, nums);
    00344   totaluse++;
    00345   /* compute new size for array part */
    00346   na = computesizes(nums, &nasize);
    00347   /* resize the table to new computed sizes */
    00348   resize(L, t, nasize, totaluse - na);
    00349 }
    00350
    00351
    00352
    00353 /*
    00354 ** }=============================================================
    00355 */
    00356
    00357
    00358 Table *luaH_new (lua_State *L, int narray, int nhash) {
    00359   Table *t = luaM_new(L, Table);
    00360   luaC_link(L, obj2gco(t), LUA_TTABLE);
    00361   t->metatable = NULL;
    00362   t->flags = cast_byte(~0);
    00363   /* temporary values (kept only if some malloc fails) */
    00364   t->array = NULL;
    00365   t->sizearray = 0;
    00366   t->lsizenode = 0;
    00367   t->node = cast(Node *, dummynode);
    00368   setarrayvector(L, t, narray);
    00369   setnodevector(L, t, nhash);
    00370   return t;
    00371 }
    00372
    00373
    00374 void luaH_free (lua_State *L, Table *t) {
    00375   if (t->node != dummynode)
    00376     luaM_freearray(L, t->node, sizenode(t), Node);
    00377   luaM_freearray(L, t->array, t->sizearray, TValue);
    00378   luaM_free(L, t);
    00379 }
    00380
    00381
    00382 static Node *getfreepos (Table *t) {
    00383   while (t->lastfree-- > t->node) {
    00384     if (ttisnil(gkey(t->lastfree)))
    00385       return t->lastfree;
    00386   }
    00387   return NULL;  /* could not find a free place */
    00388 }
    00389
    00390
    00391
    00392 /*
    00393 ** inserts a new key into a hash table; first, check whether key's main
    00394 ** position is free. If not, check whether colliding node is in its main
    00395 ** position or not: if it is not, move colliding node to an empty place and
    00396 ** put new key in its main position; otherwise (colliding node is in its main
    00397 ** position), new key goes to an empty position.
    00398 */
    00399 static TValue *newkey (lua_State *L, Table *t, const TValue *key) {
    00400   Node *mp = mainposition(t, key);
    00401   if (!ttisnil(gval(mp)) || mp == dummynode) {
    00402     Node *othern;
    00403     Node *n = getfreepos(t);  /* get a free place */
    00404     if (n == NULL) {  /* cannot find a free place? */
    00405       rehash(L, t, key);  /* grow table */
    00406       return luaH_set(L, t, key);  /* re-insert key into grown table */
    00407     }
    00408     lua_assert(n != dummynode);
    00409     othern = mainposition(t, key2tval(mp));
    00410     if (othern != mp) {  /* is colliding node out of its main position? */
    00411       /* yes; move colliding node into free position */
    00412       while (gnext(othern) != mp) othern = gnext(othern);  /* find previous */
    00413       gnext(othern) = n;  /* redo the chain with `n' in place of `mp' */
    00414       *n = *mp;  /* copy colliding node into free pos. (mp->next also goes) */
    00415       gnext(mp) = NULL;  /* now `mp' is free */
    00416       setnilvalue(gval(mp));
    00417     }
    00418     else {  /* colliding node is in its own main position */
    00419       /* new node will go into free position */
    00420       gnext(n) = gnext(mp);  /* chain new position */
    00421       gnext(mp) = n;
    00422       mp = n;
    00423     }
    00424   }
    00425   gkey(mp)->value = key->value; gkey(mp)->tt = key->tt;
    00426   luaC_barriert(L, t, key);
    00427   lua_assert(ttisnil(gval(mp)));
    00428   return gval(mp);
    00429 }
    00430
    00431
    00432 /*
    00433 ** search function for integers
    00434 */
    00435 const TValue *luaH_getnum (Table *t, int key) {
    00436   /* (1 <= key && key <= t->sizearray) */
    00437   if (cast(unsigned int, key-1) < cast(unsigned int, t->sizearray))
    00438     return &t->array[key-1];
    00439   else {
    00440     lua_Number nk = cast_num(key);
    00441     Node *n = hashnum(t, nk);
    00442     do {  /* check whether `key' is somewhere in the chain */
    00443       if (ttisnumber(gkey(n)) && luai_numeq(nvalue(gkey(n)), nk))
    00444         return gval(n);  /* that's it */
    00445       else n = gnext(n);
    00446     } while (n);
    00447     return luaO_nilobject;
    00448   }
    00449 }
    00450
    00451
    00452 /*
    00453 ** search function for strings
    00454 */
    00455 const TValue *luaH_getstr (Table *t, TString *key) {
    00456   Node *n = hashstr(t, key);
    00457   do {  /* check whether `key' is somewhere in the chain */
    00458     if (ttisstring(gkey(n)) && rawtsvalue(gkey(n)) == key)
    00459       return gval(n);  /* that's it */
    00460     else n = gnext(n);
    00461   } while (n);
    00462   return luaO_nilobject;
    00463 }
    00464
    00465
    00466 /*
    00467 ** main search function
    00468 */
    00469 const TValue *luaH_get (Table *t, const TValue *key) {
    00470   switch (ttype(key)) {
    00471     case LUA_TNIL: return luaO_nilobject;
    00472     case LUA_TSTRING: return luaH_getstr(t, rawtsvalue(key));
    00473     case LUA_TNUMBER: {
    00474       int k;
    00475       lua_Number n = nvalue(key);
    00476       lua_number2int(k, n);
    00477       if (luai_numeq(cast_num(k), nvalue(key))) /* index is int? */
    00478         return luaH_getnum(t, k);  /* use specialized version */
    00479       /* else go through */
    00480     }
    00481     default: {
    00482       Node *n = mainposition(t, key);
    00483       do {  /* check whether `key' is somewhere in the chain */
    00484         if (luaO_rawequalObj(key2tval(n), key))
    00485           return gval(n);  /* that's it */
    00486         else n = gnext(n);
    00487       } while (n);
    00488       return luaO_nilobject;
    00489     }
    00490   }
    00491 }
    00492
    00493
    00494 TValue *luaH_set (lua_State *L, Table *t, const TValue *key) {
    00495   const TValue *p = luaH_get(t, key);
    00496   t->flags = 0;
    00497   if (p != luaO_nilobject)
    00498     return cast(TValue *, p);
    00499   else {
    00500     if (ttisnil(key)) luaG_runerror(L, "table index is nil");
    00501     else if (ttisnumber(key) && luai_numisnan(nvalue(key)))
    00502       luaG_runerror(L, "table index is NaN");
    00503     return newkey(L, t, key);
    00504   }
    00505 }
    00506
    00507
    00508 TValue *luaH_setnum (lua_State *L, Table *t, int key) {
    00509   const TValue *p = luaH_getnum(t, key);
    00510   if (p != luaO_nilobject)
    00511     return cast(TValue *, p);
    00512   else {
    00513     TValue k;
    00514     setnvalue(&k, cast_num(key));
    00515     return newkey(L, t, &k);
    00516   }
    00517 }
    00518
    00519
    00520 TValue *luaH_setstr (lua_State *L, Table *t, TString *key) {
    00521   const TValue *p = luaH_getstr(t, key);
    00522   if (p != luaO_nilobject)
    00523     return cast(TValue *, p);
    00524   else {
    00525     TValue k;
    00526     setsvalue(L, &k, key);
    00527     return newkey(L, t, &k);
    00528   }
    00529 }
    00530
    00531
    00532 static int unbound_search (Table *t, unsigned int j) {
    00533   unsigned int i = j;  /* i is zero or a present index */
    00534   j++;
    00535   /* find `i' and `j' such that i is present and j is not */
    00536   while (!ttisnil(luaH_getnum(t, j))) {
    00537     i = j;
    00538     j *= 2;
    00539     if (j > cast(unsigned int, MAX_INT)) {  /* overflow? */
    00540       /* table was built with bad purposes: resort to linear search */
    00541       i = 1;
    00542       while (!ttisnil(luaH_getnum(t, i))) i++;
    00543       return i - 1;
    00544     }
    00545   }
    00546   /* now do a binary search between them */
    00547   while (j - i > 1) {
    00548     unsigned int m = (i+j)/2;
    00549     if (ttisnil(luaH_getnum(t, m))) j = m;
    00550     else i = m;
    00551   }
    00552   return i;
    00553 }
    00554
    00555
    00556 /*
    00557 ** Try to find a boundary in table `t'. A `boundary' is an integer index
    00558 ** such that t[i] is non-nil and t[i+1] is nil (and 0 if t[1] is nil).
    00559 */
    00560 int luaH_getn (Table *t) {
    00561   unsigned int j = t->sizearray;
    00562   if (j > 0 && ttisnil(&t->array[j - 1])) {
    00563     /* there is a boundary in the array part: (binary) search for it */
    00564     unsigned int i = 0;
    00565     while (j - i > 1) {
    00566       unsigned int m = (i+j)/2;
    00567       if (ttisnil(&t->array[m - 1])) j = m;
    00568       else i = m;
    00569     }
    00570     return i;
    00571   }
    00572   /* else must find a boundary in hash part */
    00573   else if (t->node == dummynode)  /* hash part is empty? */
    00574     return j;  /* that is easy... */
    00575   else return unbound_search(t, j);
    00576 }
    00577
    00578
    00579
    00580 #if defined(LUA_DEBUG)
    00581
    00582 Node *luaH_mainposition (const Table *t, const TValue *key) {
    00583   return mainposition(t, key);
    00584 }
    00585
    00586 int luaH_isdummy (Node *n) { return n == dummynode; }
    00587
    00588 #endif