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1 /*
2 ** $Id: ltable.c,v 2.118.1.4 2018/06/08 16:22:51 roberto Exp $
3 ** Lua tables (hash)
4 ** See Copyright Notice in lua.h
5 */
6 
7 #define ltable_c
8 #define LUA_CORE
9 
10 #include "lprefix.h"
11 
12 
13 /*
14 ** Implementation of tables (aka arrays, objects, or hash tables).
15 ** Tables keep its elements in two parts: an array part and a hash part.
16 ** Non-negative integer keys are all candidates to be kept in the array
17 ** part. The actual size of the array is the largest 'n' such that
18 ** more than half the slots between 1 and n are in use.
19 ** Hash uses a mix of chained scatter table with Brent's variation.
20 ** A main invariant of these tables is that, if an element is not
21 ** in its main position (i.e. the 'original' position that its hash gives
22 ** to it), then the colliding element is in its own main position.
23 ** Hence even when the load factor reaches 100%, performance remains good.
24 */
25 
26 #include <math.h>
27 #include <limits.h>
28 
29 #include "lua.h"
30 
31 #include "ldebug.h"
32 #include "ldo.h"
33 #include "lgc.h"
34 #include "lmem.h"
35 #include "lobject.h"
36 #include "lstate.h"
37 #include "lstring.h"
38 #include "ltable.h"
39 #include "lvm.h"
40 
41 
42 /*
43 ** Maximum size of array part (MAXASIZE) is 2^MAXABITS. MAXABITS is
44 ** the largest integer such that MAXASIZE fits in an unsigned int.
45 */
46 #define MAXABITS	cast_int(sizeof(int) * CHAR_BIT - 1)
47 #define MAXASIZE	(1u << MAXABITS)
48 
49 /*
50 ** Maximum size of hash part is 2^MAXHBITS. MAXHBITS is the largest
51 ** integer such that 2^MAXHBITS fits in a signed int. (Note that the
52 ** maximum number of elements in a table, 2^MAXABITS + 2^MAXHBITS, still
53 ** fits comfortably in an unsigned int.)
54 */
55 #define MAXHBITS	(MAXABITS - 1)
56 
57 
58 #define hashpow2(t,n)		(gnode(t, lmod((n), sizenode(t))))
59 
60 #define hashstr(t,str)		hashpow2(t, (str)->hash)
61 #define hashboolean(t,p)	hashpow2(t, p)
62 #define hashint(t,i)		hashpow2(t, i)
63 
64 
65 /*
66 ** for some types, it is better to avoid modulus by power of 2, as
67 ** they tend to have many 2 factors.
68 */
69 #define hashmod(t,n)	(gnode(t, ((n) % ((sizenode(t)-1)|1))))
70 
71 
72 #define hashpointer(t,p)	hashmod(t, point2uint(p))
73 
74 
75 #define dummynode		(&dummynode_)
76 
77 static const Node dummynode_ = {
78   {NILCONSTANT},  /* value */
79   {{NILCONSTANT, 0}}  /* key */
80 };
81 
82 
83 /*
84 ** Hash for floating-point numbers.
85 ** The main computation should be just
86 **     n = frexp(n, &i); return (n * INT_MAX) + i
87 ** but there are some numerical subtleties.
88 ** In a two-complement representation, INT_MAX does not has an exact
89 ** representation as a float, but INT_MIN does; because the absolute
90 ** value of 'frexp' is smaller than 1 (unless 'n' is inf/NaN), the
91 ** absolute value of the product 'frexp * -INT_MIN' is smaller or equal
92 ** to INT_MAX. Next, the use of 'unsigned int' avoids overflows when
93 ** adding 'i'; the use of '~u' (instead of '-u') avoids problems with
94 ** INT_MIN.
95 */
96 #if !defined(l_hashfloat)
l_hashfloat(lua_Number n)97 static int l_hashfloat (lua_Number n) {
98   int i;
99   lua_Integer ni;
100   n = l_mathop(frexp)(n, &i) * -cast_num(INT_MIN);
101   if (!lua_numbertointeger(n, &ni)) {  /* is 'n' inf/-inf/NaN? */
102     lua_assert(luai_numisnan(n) || l_mathop(fabs)(n) == cast_num(HUGE_VAL));
103     return 0;
104   }
105   else {  /* normal case */
106     unsigned int u = cast(unsigned int, i) + cast(unsigned int, ni);
107     return cast_int(u <= cast(unsigned int, INT_MAX) ? u : ~u);
108   }
109 }
110 #endif
111 
112 
113 /*
114 ** returns the 'main' position of an element in a table (that is, the index
115 ** of its hash value)
116 */
mainposition(const Table * t,const TValue * key)117 static Node *mainposition (const Table *t, const TValue *key) {
118   switch (ttype(key)) {
119     case LUA_TNUMINT:
120       return hashint(t, ivalue(key));
121     case LUA_TNUMFLT:
122       return hashmod(t, l_hashfloat(fltvalue(key)));
123     case LUA_TSHRSTR:
124       return hashstr(t, tsvalue(key));
125     case LUA_TLNGSTR:
126       return hashpow2(t, luaS_hashlongstr(tsvalue(key)));
127     case LUA_TBOOLEAN:
128       return hashboolean(t, bvalue(key));
129     case LUA_TLIGHTUSERDATA:
130       return hashpointer(t, pvalue(key));
131     case LUA_TLCF:
132       return hashpointer(t, fvalue(key));
133     default:
134       lua_assert(!ttisdeadkey(key));
135       return hashpointer(t, gcvalue(key));
136   }
137 }
138 
139 
140 /*
141 ** returns the index for 'key' if 'key' is an appropriate key to live in
142 ** the array part of the table, 0 otherwise.
143 */
arrayindex(const TValue * key)144 static unsigned int arrayindex (const TValue *key) {
145   if (ttisinteger(key)) {
146     lua_Integer k = ivalue(key);
147     if (0 < k && (lua_Unsigned)k <= MAXASIZE)
148       return cast(unsigned int, k);  /* 'key' is an appropriate array index */
149   }
150   return 0;  /* 'key' did not match some condition */
151 }
152 
153 
154 /*
155 ** returns the index of a 'key' for table traversals. First goes all
156 ** elements in the array part, then elements in the hash part. The
157 ** beginning of a traversal is signaled by 0.
158 */
findindex(lua_State * L,Table * t,StkId key)159 static unsigned int findindex (lua_State *L, Table *t, StkId key) {
160   unsigned int i;
161   if (ttisnil(key)) return 0;  /* first iteration */
162   i = arrayindex(key);
163   if (i != 0 && i <= t->sizearray)  /* is 'key' inside array part? */
164     return i;  /* yes; that's the index */
165   else {
166     int nx;
167     Node *n = mainposition(t, key);
168     for (;;) {  /* check whether 'key' is somewhere in the chain */
169       /* key may be dead already, but it is ok to use it in 'next' */
170       if (luaV_rawequalobj(gkey(n), key) ||
171             (ttisdeadkey(gkey(n)) && iscollectable(key) &&
172              deadvalue(gkey(n)) == gcvalue(key))) {
173         i = cast_int(n - gnode(t, 0));  /* key index in hash table */
174         /* hash elements are numbered after array ones */
175         return (i + 1) + t->sizearray;
176       }
177       nx = gnext(n);
178       if (nx == 0)
179         luaG_runerror(L, "invalid key to 'next'");  /* key not found */
180       else n += nx;
181     }
182   }
183 }
184 
185 
luaH_next(lua_State * L,Table * t,StkId key)186 int luaH_next (lua_State *L, Table *t, StkId key) {
187   unsigned int i = findindex(L, t, key);  /* find original element */
188   for (; i < t->sizearray; i++) {  /* try first array part */
189     if (!ttisnil(&t->array[i])) {  /* a non-nil value? */
190       setivalue(key, i + 1);
191       setobj2s(L, key+1, &t->array[i]);
192       return 1;
193     }
194   }
195   for (i -= t->sizearray; cast_int(i) < sizenode(t); i++) {  /* hash part */
196     if (!ttisnil(gval(gnode(t, i)))) {  /* a non-nil value? */
197       setobj2s(L, key, gkey(gnode(t, i)));
198       setobj2s(L, key+1, gval(gnode(t, i)));
199       return 1;
200     }
201   }
202   return 0;  /* no more elements */
203 }
204 
205 
206 /*
207 ** {=============================================================
208 ** Rehash
209 ** ==============================================================
210 */
211 
212 /*
213 ** Compute the optimal size for the array part of table 't'. 'nums' is a
214 ** "count array" where 'nums[i]' is the number of integers in the table
215 ** between 2^(i - 1) + 1 and 2^i. 'pna' enters with the total number of
216 ** integer keys in the table and leaves with the number of keys that
217 ** will go to the array part; return the optimal size.
218 */
computesizes(unsigned int nums[],unsigned int * pna)219 static unsigned int computesizes (unsigned int nums[], unsigned int *pna) {
220   int i;
221   unsigned int twotoi;  /* 2^i (candidate for optimal size) */
222   unsigned int a = 0;  /* number of elements smaller than 2^i */
223   unsigned int na = 0;  /* number of elements to go to array part */
224   unsigned int optimal = 0;  /* optimal size for array part */
225   /* loop while keys can fill more than half of total size */
226   for (i = 0, twotoi = 1;
227        twotoi > 0 && *pna > twotoi / 2;
228        i++, twotoi *= 2) {
229     if (nums[i] > 0) {
230       a += nums[i];
231       if (a > twotoi/2) {  /* more than half elements present? */
232         optimal = twotoi;  /* optimal size (till now) */
233         na = a;  /* all elements up to 'optimal' will go to array part */
234       }
235     }
236   }
237   lua_assert((optimal == 0 || optimal / 2 < na) && na <= optimal);
238   *pna = na;
239   return optimal;
240 }
241 
242 
countint(const TValue * key,unsigned int * nums)243 static int countint (const TValue *key, unsigned int *nums) {
244   unsigned int k = arrayindex(key);
245   if (k != 0) {  /* is 'key' an appropriate array index? */
246     nums[luaO_ceillog2(k)]++;  /* count as such */
247     return 1;
248   }
249   else
250     return 0;
251 }
252 
253 
254 /*
255 ** Count keys in array part of table 't': Fill 'nums[i]' with
256 ** number of keys that will go into corresponding slice and return
257 ** total number of non-nil keys.
258 */
numusearray(const Table * t,unsigned int * nums)259 static unsigned int numusearray (const Table *t, unsigned int *nums) {
260   int lg;
261   unsigned int ttlg;  /* 2^lg */
262   unsigned int ause = 0;  /* summation of 'nums' */
263   unsigned int i = 1;  /* count to traverse all array keys */
264   /* traverse each slice */
265   for (lg = 0, ttlg = 1; lg <= MAXABITS; lg++, ttlg *= 2) {
266     unsigned int lc = 0;  /* counter */
267     unsigned int lim = ttlg;
268     if (lim > t->sizearray) {
269       lim = t->sizearray;  /* adjust upper limit */
270       if (i > lim)
271         break;  /* no more elements to count */
272     }
273     /* count elements in range (2^(lg - 1), 2^lg] */
274     for (; i <= lim; i++) {
275       if (!ttisnil(&t->array[i-1]))
276         lc++;
277     }
278     nums[lg] += lc;
279     ause += lc;
280   }
281   return ause;
282 }
283 
284 
numusehash(const Table * t,unsigned int * nums,unsigned int * pna)285 static int numusehash (const Table *t, unsigned int *nums, unsigned int *pna) {
286   int totaluse = 0;  /* total number of elements */
287   int ause = 0;  /* elements added to 'nums' (can go to array part) */
288   int i = sizenode(t);
289   while (i--) {
290     Node *n = &t->node[i];
291     if (!ttisnil(gval(n))) {
292       ause += countint(gkey(n), nums);
293       totaluse++;
294     }
295   }
296   *pna += ause;
297   return totaluse;
298 }
299 
300 
setarrayvector(lua_State * L,Table * t,unsigned int size)301 static void setarrayvector (lua_State *L, Table *t, unsigned int size) {
302   unsigned int i;
303   luaM_reallocvector(L, t->array, t->sizearray, size, TValue);
304   for (i=t->sizearray; i<size; i++)
305      setnilvalue(&t->array[i]);
306   t->sizearray = size;
307 }
308 
309 
setnodevector(lua_State * L,Table * t,unsigned int size)310 static void setnodevector (lua_State *L, Table *t, unsigned int size) {
311   if (size == 0) {  /* no elements to hash part? */
312     t->node = cast(Node *, dummynode);  /* use common 'dummynode' */
313     t->lsizenode = 0;
314     t->lastfree = NULL;  /* signal that it is using dummy node */
315   }
316   else {
317     int i;
318     int lsize = luaO_ceillog2(size);
319     if (lsize > MAXHBITS)
320       luaG_runerror(L, "table overflow");
321     size = twoto(lsize);
322     t->node = luaM_newvector(L, size, Node);
323     for (i = 0; i < (int)size; i++) {
324       Node *n = gnode(t, i);
325       gnext(n) = 0;
326       setnilvalue(wgkey(n));
327       setnilvalue(gval(n));
328     }
329     t->lsizenode = cast_byte(lsize);
330     t->lastfree = gnode(t, size);  /* all positions are free */
331   }
332 }
333 
334 
335 typedef struct {
336   Table *t;
337   unsigned int nhsize;
338 } AuxsetnodeT;
339 
340 
auxsetnode(lua_State * L,void * ud)341 static void auxsetnode (lua_State *L, void *ud) {
342   AuxsetnodeT *asn = cast(AuxsetnodeT *, ud);
343   setnodevector(L, asn->t, asn->nhsize);
344 }
345 
346 
luaH_resize(lua_State * L,Table * t,unsigned int nasize,unsigned int nhsize)347 void luaH_resize (lua_State *L, Table *t, unsigned int nasize,
348                                           unsigned int nhsize) {
349   unsigned int i;
350   int j;
351   AuxsetnodeT asn;
352   unsigned int oldasize = t->sizearray;
353   int oldhsize = allocsizenode(t);
354   Node *nold = t->node;  /* save old hash ... */
355   if (nasize > oldasize)  /* array part must grow? */
356     setarrayvector(L, t, nasize);
357   /* create new hash part with appropriate size */
358   asn.t = t; asn.nhsize = nhsize;
359   if (luaD_rawrunprotected(L, auxsetnode, &asn) != LUA_OK) {  /* mem. error? */
360     setarrayvector(L, t, oldasize);  /* array back to its original size */
361     luaD_throw(L, LUA_ERRMEM);  /* rethrow memory error */
362   }
363   if (nasize < oldasize) {  /* array part must shrink? */
364     t->sizearray = nasize;
365     /* re-insert elements from vanishing slice */
366     for (i=nasize; i<oldasize; i++) {
367       if (!ttisnil(&t->array[i]))
368         luaH_setint(L, t, i + 1, &t->array[i]);
369     }
370     /* shrink array */
371     luaM_reallocvector(L, t->array, oldasize, nasize, TValue);
372   }
373   /* re-insert elements from hash part */
374   for (j = oldhsize - 1; j >= 0; j--) {
375     Node *old = nold + j;
376     if (!ttisnil(gval(old))) {
377       /* doesn't need barrier/invalidate cache, as entry was
378          already present in the table */
379       setobjt2t(L, luaH_set(L, t, gkey(old)), gval(old));
380     }
381   }
382   if (oldhsize > 0)  /* not the dummy node? */
383     luaM_freearray(L, nold, cast(size_t, oldhsize)); /* free old hash */
384 }
385 
386 
luaH_resizearray(lua_State * L,Table * t,unsigned int nasize)387 void luaH_resizearray (lua_State *L, Table *t, unsigned int nasize) {
388   int nsize = allocsizenode(t);
389   luaH_resize(L, t, nasize, nsize);
390 }
391 
392 /*
393 ** nums[i] = number of keys 'k' where 2^(i - 1) < k <= 2^i
394 */
rehash(lua_State * L,Table * t,const TValue * ek)395 static void rehash (lua_State *L, Table *t, const TValue *ek) {
396   unsigned int asize;  /* optimal size for array part */
397   unsigned int na;  /* number of keys in the array part */
398   unsigned int nums[MAXABITS + 1];
399   int i;
400   int totaluse;
401   for (i = 0; i <= MAXABITS; i++) nums[i] = 0;  /* reset counts */
402   na = numusearray(t, nums);  /* count keys in array part */
403   totaluse = na;  /* all those keys are integer keys */
404   totaluse += numusehash(t, nums, &na);  /* count keys in hash part */
405   /* count extra key */
406   na += countint(ek, nums);
407   totaluse++;
408   /* compute new size for array part */
409   asize = computesizes(nums, &na);
410   /* resize the table to new computed sizes */
411   luaH_resize(L, t, asize, totaluse - na);
412 }
413 
414 
415 
416 /*
417 ** }=============================================================
418 */
419 
420 
luaH_new(lua_State * L)421 Table *luaH_new (lua_State *L) {
422   GCObject *o = luaC_newobj(L, LUA_TTABLE, sizeof(Table));
423   Table *t = gco2t(o);
424   t->metatable = NULL;
425   t->flags = cast_byte(~0);
426   t->array = NULL;
427   t->sizearray = 0;
428   setnodevector(L, t, 0);
429   return t;
430 }
431 
432 
luaH_free(lua_State * L,Table * t)433 void luaH_free (lua_State *L, Table *t) {
434   if (!isdummy(t))
435     luaM_freearray(L, t->node, cast(size_t, sizenode(t)));
436   luaM_freearray(L, t->array, t->sizearray);
437   luaM_free(L, t);
438 }
439 
440 
getfreepos(Table * t)441 static Node *getfreepos (Table *t) {
442   if (!isdummy(t)) {
443     while (t->lastfree > t->node) {
444       t->lastfree--;
445       if (ttisnil(gkey(t->lastfree)))
446         return t->lastfree;
447     }
448   }
449   return NULL;  /* could not find a free place */
450 }
451 
452 
453 
454 /*
455 ** inserts a new key into a hash table; first, check whether key's main
456 ** position is free. If not, check whether colliding node is in its main
457 ** position or not: if it is not, move colliding node to an empty place and
458 ** put new key in its main position; otherwise (colliding node is in its main
459 ** position), new key goes to an empty position.
460 */
luaH_newkey(lua_State * L,Table * t,const TValue * key)461 TValue *luaH_newkey (lua_State *L, Table *t, const TValue *key) {
462   Node *mp;
463   TValue aux;
464   if (ttisnil(key)) luaG_runerror(L, "table index is nil");
465   else if (ttisfloat(key)) {
466     lua_Integer k;
467     if (luaV_tointeger(key, &k, 0)) {  /* does index fit in an integer? */
468       setivalue(&aux, k);
469       key = &aux;  /* insert it as an integer */
470     }
471     else if (luai_numisnan(fltvalue(key)))
472       luaG_runerror(L, "table index is NaN");
473   }
474   mp = mainposition(t, key);
475   if (!ttisnil(gval(mp)) || isdummy(t)) {  /* main position is taken? */
476     Node *othern;
477     Node *f = getfreepos(t);  /* get a free place */
478     if (f == NULL) {  /* cannot find a free place? */
479       rehash(L, t, key);  /* grow table */
480       /* whatever called 'newkey' takes care of TM cache */
481       return luaH_set(L, t, key);  /* insert key into grown table */
482     }
483     lua_assert(!isdummy(t));
484     othern = mainposition(t, gkey(mp));
485     if (othern != mp) {  /* is colliding node out of its main position? */
486       /* yes; move colliding node into free position */
487       while (othern + gnext(othern) != mp)  /* find previous */
488         othern += gnext(othern);
489       gnext(othern) = cast_int(f - othern);  /* rechain to point to 'f' */
490       *f = *mp;  /* copy colliding node into free pos. (mp->next also goes) */
491       if (gnext(mp) != 0) {
492         gnext(f) += cast_int(mp - f);  /* correct 'next' */
493         gnext(mp) = 0;  /* now 'mp' is free */
494       }
495       setnilvalue(gval(mp));
496     }
497     else {  /* colliding node is in its own main position */
498       /* new node will go into free position */
499       if (gnext(mp) != 0)
500         gnext(f) = cast_int((mp + gnext(mp)) - f);  /* chain new position */
501       else lua_assert(gnext(f) == 0);
502       gnext(mp) = cast_int(f - mp);
503       mp = f;
504     }
505   }
506   setnodekey(L, &mp->i_key, key);
507   luaC_barrierback(L, t, key);
508   lua_assert(ttisnil(gval(mp)));
509   return gval(mp);
510 }
511 
512 
513 /*
514 ** search function for integers
515 */
luaH_getint(Table * t,lua_Integer key)516 const TValue *luaH_getint (Table *t, lua_Integer key) {
517   /* (1 <= key && key <= t->sizearray) */
518   if (l_castS2U(key) - 1 < t->sizearray)
519     return &t->array[key - 1];
520   else {
521     Node *n = hashint(t, key);
522     for (;;) {  /* check whether 'key' is somewhere in the chain */
523       if (ttisinteger(gkey(n)) && ivalue(gkey(n)) == key)
524         return gval(n);  /* that's it */
525       else {
526         int nx = gnext(n);
527         if (nx == 0) break;
528         n += nx;
529       }
530     }
531     return luaO_nilobject;
532   }
533 }
534 
535 
536 /*
537 ** search function for short strings
538 */
luaH_getshortstr(Table * t,TString * key)539 const TValue *luaH_getshortstr (Table *t, TString *key) {
540   Node *n = hashstr(t, key);
541   lua_assert(key->tt == LUA_TSHRSTR);
542   for (;;) {  /* check whether 'key' is somewhere in the chain */
543     const TValue *k = gkey(n);
544     if (ttisshrstring(k) && eqshrstr(tsvalue(k), key))
545       return gval(n);  /* that's it */
546     else {
547       int nx = gnext(n);
548       if (nx == 0)
549         return luaO_nilobject;  /* not found */
550       n += nx;
551     }
552   }
553 }
554 
555 
556 /*
557 ** "Generic" get version. (Not that generic: not valid for integers,
558 ** which may be in array part, nor for floats with integral values.)
559 */
getgeneric(Table * t,const TValue * key)560 static const TValue *getgeneric (Table *t, const TValue *key) {
561   Node *n = mainposition(t, key);
562   for (;;) {  /* check whether 'key' is somewhere in the chain */
563     if (luaV_rawequalobj(gkey(n), key))
564       return gval(n);  /* that's it */
565     else {
566       int nx = gnext(n);
567       if (nx == 0)
568         return luaO_nilobject;  /* not found */
569       n += nx;
570     }
571   }
572 }
573 
574 
luaH_getstr(Table * t,TString * key)575 const TValue *luaH_getstr (Table *t, TString *key) {
576   if (key->tt == LUA_TSHRSTR)
577     return luaH_getshortstr(t, key);
578   else {  /* for long strings, use generic case */
579     TValue ko;
580     setsvalue(cast(lua_State *, NULL), &ko, key);
581     return getgeneric(t, &ko);
582   }
583 }
584 
585 
586 /*
587 ** main search function
588 */
luaH_get(Table * t,const TValue * key)589 const TValue *luaH_get (Table *t, const TValue *key) {
590   switch (ttype(key)) {
591     case LUA_TSHRSTR: return luaH_getshortstr(t, tsvalue(key));
592     case LUA_TNUMINT: return luaH_getint(t, ivalue(key));
593     case LUA_TNIL: return luaO_nilobject;
594     case LUA_TNUMFLT: {
595       lua_Integer k;
596       if (luaV_tointeger(key, &k, 0)) /* index is int? */
597         return luaH_getint(t, k);  /* use specialized version */
598       /* else... */
599     }  /* FALLTHROUGH */
600     default:
601       return getgeneric(t, key);
602   }
603 }
604 
605 
606 /*
607 ** beware: when using this function you probably need to check a GC
608 ** barrier and invalidate the TM cache.
609 */
luaH_set(lua_State * L,Table * t,const TValue * key)610 TValue *luaH_set (lua_State *L, Table *t, const TValue *key) {
611   const TValue *p = luaH_get(t, key);
612   if (p != luaO_nilobject)
613     return cast(TValue *, p);
614   else return luaH_newkey(L, t, key);
615 }
616 
617 
luaH_setint(lua_State * L,Table * t,lua_Integer key,TValue * value)618 void luaH_setint (lua_State *L, Table *t, lua_Integer key, TValue *value) {
619   const TValue *p = luaH_getint(t, key);
620   TValue *cell;
621   if (p != luaO_nilobject)
622     cell = cast(TValue *, p);
623   else {
624     TValue k;
625     setivalue(&k, key);
626     cell = luaH_newkey(L, t, &k);
627   }
628   setobj2t(L, cell, value);
629 }
630 
631 
unbound_search(Table * t,lua_Unsigned j)632 static lua_Unsigned unbound_search (Table *t, lua_Unsigned j) {
633   lua_Unsigned i = j;  /* i is zero or a present index */
634   j++;
635   /* find 'i' and 'j' such that i is present and j is not */
636   while (!ttisnil(luaH_getint(t, j))) {
637     i = j;
638     if (j > l_castS2U(LUA_MAXINTEGER) / 2) {  /* overflow? */
639       /* table was built with bad purposes: resort to linear search */
640       i = 1;
641       while (!ttisnil(luaH_getint(t, i))) i++;
642       return i - 1;
643     }
644     j *= 2;
645   }
646   /* now do a binary search between them */
647   while (j - i > 1) {
648     lua_Unsigned m = (i+j)/2;
649     if (ttisnil(luaH_getint(t, m))) j = m;
650     else i = m;
651   }
652   return i;
653 }
654 
655 
656 /*
657 ** Try to find a boundary in table 't'. A 'boundary' is an integer index
658 ** such that t[i] is non-nil and t[i+1] is nil (and 0 if t[1] is nil).
659 */
luaH_getn(Table * t)660 lua_Unsigned luaH_getn (Table *t) {
661   unsigned int j = t->sizearray;
662   if (j > 0 && ttisnil(&t->array[j - 1])) {
663     /* there is a boundary in the array part: (binary) search for it */
664     unsigned int i = 0;
665     while (j - i > 1) {
666       unsigned int m = (i+j)/2;
667       if (ttisnil(&t->array[m - 1])) j = m;
668       else i = m;
669     }
670     return i;
671   }
672   /* else must find a boundary in hash part */
673   else if (isdummy(t))  /* hash part is empty? */
674     return j;  /* that is easy... */
675   else return unbound_search(t, j);
676 }
677 
678 
679 
680 #if defined(LUA_DEBUG)
681 
luaH_mainposition(const Table * t,const TValue * key)682 Node *luaH_mainposition (const Table *t, const TValue *key) {
683   return mainposition(t, key);
684 }
685 
luaH_isdummy(const Table * t)686 int luaH_isdummy (const Table *t) { return isdummy(t); }
687 
688 #endif
689