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** $Id: ltable.c $

** Lua tables (hash)

** See Copyright Notice in lua.h

#define ltable_c

#define LUA_CORE

#include "lprefix.h"

** Implementation of tables (aka arrays, objects, or hash tables).

** Tables keep its elements in two parts: an array part and a hash part.

** Non-negative integer keys are all candidates to be kept in the array

** part. The actual size of the array is the largest 'n' such that

** more than half the slots between 1 and n are in use.

** Hash 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.

** Hence even when the load factor reaches 100%, performance remains good.

#include <math.h>

#include <limits.h>

#include "lua.h"

#include "ldebug.h"

#include "ldo.h"

#include "lgc.h"

#include "lmem.h"

#include "lobject.h"

#include "lstate.h"

#include "lstring.h"

#include "ltable.h"

#include "lvm.h"

** MAXABITS is the largest integer such that MAXASIZE fits in an

** unsigned int.

#define MAXABITS cast_int(sizeof(int) * CHAR_BIT - 1)

** MAXASIZE is the maximum size of the array part. It is the minimum

** between 2^MAXABITS and the maximum size that, measured in bytes,

** fits in a 'size_t'.

#define MAXASIZE luaM_limitN(1u << MAXABITS, TValue)

** MAXHBITS is the largest integer such that 2^MAXHBITS fits in a

** signed int.

#define MAXHBITS (MAXABITS - 1)

** MAXHSIZE is the maximum size of the hash part. It is the minimum

** between 2^MAXHBITS and the maximum size such that, measured in bytes,

** it fits in a 'size_t'.

#define MAXHSIZE luaM_limitN(1u << MAXHBITS, Node)

#define hashpow2(t,n) (gnode(t, lmod((n), sizenode(t))))

#define hashstr(t,str) hashpow2(t, (str)->hash)

#define hashboolean(t,p) hashpow2(t, p)

#define hashint(t,i) hashpow2(t, i)

** for some types, it is better to avoid modulus by power of 2, as

** they tend to have many 2 factors.

#define hashmod(t,n) (gnode(t, ((n) % ((sizenode(t)-1)|1))))

#define hashpointer(t,p) hashmod(t, point2uint(p))

#define dummynode (&dummynode_)

static const Node dummynode_ = {

{{NULL}, LUA_TEMPTY, /* value's value and type */

LUA_TNIL, 0, {NULL}} /* key type, next, and key value */

};

static const TValue absentkey = {ABSTKEYCONSTANT};

** Hash for floating-point numbers.

** The main computation should be just

** n = frexp(n, &i); return (n * INT_MAX) + i

** but there are some numerical subtleties.

** In a two-complement representation, INT_MAX does not has an exact

** representation as a float, but INT_MIN does; because the absolute

** value of 'frexp' is smaller than 1 (unless 'n' is inf/NaN), the

** absolute value of the product 'frexp * -INT_MIN' is smaller or equal

** to INT_MAX. Next, the use of 'unsigned int' avoids overflows when

** adding 'i'; the use of '~u' (instead of '-u') avoids problems with

** INT_MIN.

#if !defined(l_hashfloat)

static int l_hashfloat (lua_Number n) {

int i;

lua_Integer ni;

n = l_mathop(frexp)(n, &i) * -cast_num(INT_MIN);

if (!lua_numbertointeger(n, &ni)) { /* is 'n' inf/-inf/NaN? */

lua_assert(luai_numisnan(n) || l_mathop(fabs)(n) == cast_num(HUGE_VAL));

return 0;

}

else { /* normal case */

unsigned int u = cast_uint(i) + cast_uint(ni);

return cast_int(u <= cast_uint(INT_MAX) ? u : ~u);

}

#endif

** returns the 'main' position of an element in a table (that is,

** the index of its hash value). The key comes broken (tag in 'ktt'

** and value in 'vkl') so that we can call it on keys inserted into

** nodes.

static Node *mainposition (const Table *t, int ktt, const Value *kvl) {

switch (withvariant(ktt)) {

case LUA_TNUMINT:

return hashint(t, ivalueraw(*kvl));

case LUA_TNUMFLT:

return hashmod(t, l_hashfloat(fltvalueraw(*kvl)));

case LUA_TSHRSTR:

return hashstr(t, tsvalueraw(*kvl));

case LUA_TLNGSTR:

return hashpow2(t, luaS_hashlongstr(tsvalueraw(*kvl)));

case LUA_TBOOLEAN:

return hashboolean(t, bvalueraw(*kvl));

case LUA_TLIGHTUSERDATA:

return hashpointer(t, pvalueraw(*kvl));

case LUA_TLCF:

return hashpointer(t, fvalueraw(*kvl));

default:

return hashpointer(t, gcvalueraw(*kvl));

}

static Node *mainpositionTV (const Table *t, const TValue *key) {

return mainposition(t, rawtt(key), valraw(key));

}

** Check whether key 'k1' is equal to the key in node 'n2'.

** This equality is raw, so there are no metamethods. Floats

** with integer values have been normalized, so integers cannot

** be equal to floats. It is assumed that 'eqshrstr' is simply

** pointer equality, so that short strings are handled in the

** default case.

static int equalkey (const TValue *k1, const Node *n2) {

if (rawtt(k1) != keytt(n2)) /* not the same variants? */

return 0; /* cannot be same key */

switch (ttypetag(k1)) {

case LUA_TNIL:

return 1;

case LUA_TNUMINT:

return (ivalue(k1) == keyival(n2));

case LUA_TNUMFLT:

return luai_numeq(fltvalue(k1), fltvalueraw(keyval(n2)));

case LUA_TBOOLEAN:

return bvalue(k1) == bvalueraw(keyval(n2));

case LUA_TLIGHTUSERDATA:

return pvalue(k1) == pvalueraw(keyval(n2));

case LUA_TLCF:

return fvalue(k1) == fvalueraw(keyval(n2));

case LUA_TLNGSTR:

return luaS_eqlngstr(tsvalue(k1), keystrval(n2));

default:

return gcvalue(k1) == gcvalueraw(keyval(n2));

}

** True if value of 'alimit' is equal to the real size of the array

** part of table 't'. (Otherwise, the array part must be larger than

** 'alimit'.)

#define limitequalsasize(t) (isrealasize(t) || ispow2((t)->alimit))

** Returns the real size of the 'array' array

LUAI_FUNC unsigned int luaH_realasize (const Table *t) {

if (limitequalsasize(t))

return t->alimit; /* this is the size */

else {

unsigned int size = t->alimit;

/* compute the smallest power of 2 not smaller than 'n' */

size |= (size >> 1);

size |= (size >> 2);

size |= (size >> 4);

size |= (size >> 8);

size |= (size >> 16);

#if (UINT_MAX >> 30) > 3

size |= (size >> 32); /* unsigned int has more than 32 bits */

#endif

size++;

lua_assert(ispow2(size) && size/2 < t->alimit && t->alimit < size);

return size;

}

** Check whether real size of the array is a power of 2.

** (If it is not, 'alimit' cannot be changed to any other value

** without changing the real size.)

static int ispow2realasize (const Table *t) {

return (!isrealasize(t) || ispow2(t->alimit));

}

static unsigned int setlimittosize (Table *t) {

t->alimit = luaH_realasize(t);

setrealasize(t);

return t->alimit;

}

#define limitasasize(t) check_exp(isrealasize(t), t->alimit)

** "Generic" get version. (Not that generic: not valid for integers,

** which may be in array part, nor for floats with integral values.)

static const TValue *getgeneric (Table *t, const TValue *key) {

Node *n = mainpositionTV(t, key);

for (;;) { /* check whether 'key' is somewhere in the chain */

if (equalkey(key, n))

return gval(n); /* that's it */

else {

int nx = gnext(n);

if (nx == 0)

return &absentkey; /* not found */

n += nx;

}

** returns the index for 'k' if 'k' is an appropriate key to live in

** the array part of a table, 0 otherwise.

static unsigned int arrayindex (lua_Integer k) {

if (l_castS2U(k) - 1u < MAXASIZE) /* 'k' in [1, MAXASIZE]? */

return cast_uint(k); /* 'key' is an appropriate array index */

else

return 0;

}

** returns the index of a 'key' for table traversals. First goes all

** elements in the array part, then elements in the hash part. The

** beginning of a traversal is signaled by 0.

static unsigned int findindex (lua_State *L, Table *t, TValue *key,

unsigned int asize) {

unsigned int i;

if (ttisnil(key)) return 0; /* first iteration */

i = ttisinteger(key) ? arrayindex(ivalue(key)) : 0;

if (i - 1u < asize) /* is 'key' inside array part? */

return i; /* yes; that's the index */

else {

const TValue *n = getgeneric(t, key);

if (unlikely(isabstkey(n)))

luaG_runerror(L, "invalid key to 'next'"); /* key not found */

i = cast_int(nodefromval(n) - gnode(t, 0)); /* key index in hash table */

/* hash elements are numbered after array ones */

return (i + 1) + asize;

}

int luaH_next (lua_State *L, Table *t, StkId key) {

unsigned int asize = luaH_realasize(t);

unsigned int i = findindex(L, t, s2v(key), asize); /* find original key */

for (; i < asize; i++) { /* try first array part */

if (!isempty(&t->array[i])) { /* a non-empty entry? */

setivalue(s2v(key), i + 1);

setobj2s(L, key + 1, &t->array[i]);

return 1;

}

for (i -= asize; cast_int(i) < sizenode(t); i++) { /* hash part */

if (!isempty(gval(gnode(t, i)))) { /* a non-empty entry? */

Node *n = gnode(t, i);

getnodekey(L, s2v(key), n);

setobj2s(L, key + 1, gval(n));

return 1;

}

return 0; /* no more elements */

}

static void freehash (lua_State *L, Table *t) {

if (!isdummy(t))

luaM_freearray(L, t->node, cast_sizet(sizenode(t)));

}

** {=============================================================

** Rehash

** ==============================================================

** Compute the optimal size for the array part of table 't'. 'nums' is a

** "count array" where 'nums[i]' is the number of integers in the table

** between 2^(i - 1) + 1 and 2^i. 'pna' enters with the total number of

** integer keys in the table and leaves with the number of keys that

** will go to the array part; return the optimal size. (The condition

** 'twotoi > 0' in the for loop stops the loop if 'twotoi' overflows.)

static unsigned int computesizes (unsigned int nums[], unsigned int *pna) {

int i;

unsigned int twotoi; /* 2^i (candidate for optimal size) */

unsigned int a = 0; /* number of elements smaller than 2^i */

unsigned int na = 0; /* number of elements to go to array part */

unsigned int optimal = 0; /* optimal size for array part */

/* loop while keys can fill more than half of total size */

for (i = 0, twotoi = 1;

twotoi > 0 && *pna > twotoi / 2;

i++, twotoi *= 2) {

a += nums[i];

if (a > twotoi/2) { /* more than half elements present? */

optimal = twotoi; /* optimal size (till now) */

na = a; /* all elements up to 'optimal' will go to array part */

}

lua_assert((optimal == 0 || optimal / 2 < na) && na <= optimal);

*pna = na;

return optimal;

}

static int countint (lua_Integer key, unsigned int *nums) {

unsigned int k = arrayindex(key);

if (k != 0) { /* is 'key' an appropriate array index? */

nums[luaO_ceillog2(k)]++; /* count as such */

return 1;

}

else

return 0;

}

** Count keys in array part of table 't': Fill 'nums[i]' with

** number of keys that will go into corresponding slice and return

** total number of non-nil keys.

static unsigned int numusearray (const Table *t, unsigned int *nums) {

int lg;

unsigned int ttlg; /* 2^lg */

unsigned int ause = 0; /* summation of 'nums' */

unsigned int i = 1; /* count to traverse all array keys */

unsigned int asize = limitasasize(t); /* real array size */

/* traverse each slice */

for (lg = 0, ttlg = 1; lg <= MAXABITS; lg++, ttlg *= 2) {

unsigned int lc = 0; /* counter */

unsigned int lim = ttlg;

if (lim > asize) {

lim = asize; /* adjust upper limit */

if (i > lim)

break; /* no more elements to count */

}

/* count elements in range (2^(lg - 1), 2^lg] */

for (; i <= lim; i++) {

if (!isempty(&t->array[i-1]))

lc++;

}

nums[lg] += lc;

ause += lc;

}

return ause;

}

static int numusehash (const Table *t, unsigned int *nums, unsigned int *pna) {

int totaluse = 0; /* total number of elements */

int ause = 0; /* elements added to 'nums' (can go to array part) */

int i = sizenode(t);

while (i--) {

Node *n = &t->node[i];

if (!isempty(gval(n))) {

if (keyisinteger(n))

ause += countint(keyival(n), nums);

totaluse++;

}

*pna += ause;

return totaluse;

}

** Creates an array for the hash part of a table with the given

** size, or reuses the dummy node if size is zero.

** The computation for size overflow is in two steps: the first

** comparison ensures that the shift in the second one does not

** overflow.

static void setnodevector (lua_State *L, Table *t, unsigned int size) {

if (size == 0) { /* no elements to hash part? */

t->node = cast(Node *, dummynode); /* use common 'dummynode' */

t->lsizenode = 0;

t->lastfree = NULL; /* signal that it is using dummy node */

}

else {

int i;

int lsize = luaO_ceillog2(size);

if (lsize > MAXHBITS || (1u << lsize) > MAXHSIZE)

luaG_runerror(L, "table overflow");

size = twoto(lsize);

t->node = luaM_newvector(L, size, Node);

for (i = 0; i < (int)size; i++) {

Node *n = gnode(t, i);

gnext(n) = 0;

setnilkey(n);

setempty(gval(n));

}

t->lsizenode = cast_byte(lsize);

t->lastfree = gnode(t, size); /* all positions are free */

}

** (Re)insert all elements from the hash part of 'ot' into table 't'.

static void reinsert (lua_State *L, Table *ot, Table *t) {

int j;

int size = sizenode(ot);

for (j = 0; j < size; j++) {

Node *old = gnode(ot, j);

if (!isempty(gval(old))) {

/* doesn't need barrier/invalidate cache, as entry was

already present in the table */

TValue k;

getnodekey(L, &k, old);

setobjt2t(L, luaH_set(L, t, &k), gval(old));

}

** Exchange the hash part of 't1' and 't2'.

static void exchangehashpart (Table *t1, Table *t2) {

lu_byte lsizenode = t1->lsizenode;

Node *node = t1->node;

Node *lastfree = t1->lastfree;

t1->lsizenode = t2->lsizenode;

t1->node = t2->node;

t1->lastfree = t2->lastfree;

t2->lsizenode = lsizenode;

t2->node = node;

t2->lastfree = lastfree;

}

** Resize table 't' for the new given sizes. Both allocations (for

** the hash part and for the array part) can fail, which creates some

** subtleties. If the first allocation, for the hash part, fails, an

** error is raised and that is it. Otherwise, it copies the elements from

** the shrinking part of the array (if it is shrinking) into the new

** hash. Then it reallocates the array part. If that fails, the table

** is in its original state; the function frees the new hash part and then

** raises the allocation error. Otherwise, it sets the new hash part

** into the table, initializes the new part of the array (if any) with

** nils and reinserts the elements of the old hash back into the new

** parts of the table.

void luaH_resize (lua_State *L, Table *t, unsigned int newasize,

unsigned int nhsize) {

unsigned int i;

Table newt; /* to keep the new hash part */

unsigned int oldasize = setlimittosize(t);

TValue *newarray;

/* create new hash part with appropriate size into 'newt' */

setnodevector(L, &newt, nhsize);

if (newasize < oldasize) { /* will array shrink? */

t->alimit = newasize; /* pretend array has new size... */

exchangehashpart(t, &newt); /* and new hash */

/* re-insert into the new hash the elements from vanishing slice */

for (i = newasize; i < oldasize; i++) {

if (!isempty(&t->array[i]))

luaH_setint(L, t, i + 1, &t->array[i]);

}

t->alimit = oldasize; /* restore current size... */

exchangehashpart(t, &newt); /* and hash (in case of errors) */

}

/* allocate new array */

newarray = luaM_reallocvector(L, t->array, oldasize, newasize, TValue);

if (unlikely(newarray == NULL && newasize > 0)) { /* allocation failed? */

freehash(L, &newt); /* release new hash part */

luaM_error(L); /* raise error (with array unchanged) */

}

/* allocation ok; initialize new part of the array */

exchangehashpart(t, &newt); /* 't' has the new hash ('newt' has the old) */

t->array = newarray; /* set new array part */

t->alimit = newasize;

for (i = oldasize; i < newasize; i++) /* clear new slice of the array */

setempty(&t->array[i]);

/* re-insert elements from old hash part into new parts */

reinsert(L, &newt, t); /* 'newt' now has the old hash */

freehash(L, &newt); /* free old hash part */

}

void luaH_resizearray (lua_State *L, Table *t, unsigned int nasize) {

int nsize = allocsizenode(t);

luaH_resize(L, t, nasize, nsize);

}

** nums[i] = number of keys 'k' where 2^(i - 1) < k <= 2^i

static void rehash (lua_State *L, Table *t, const TValue *ek) {

unsigned int asize; /* optimal size for array part */

unsigned int na; /* number of keys in the array part */

unsigned int nums[MAXABITS + 1];

int i;

int totaluse;

for (i = 0; i <= MAXABITS; i++) nums[i] = 0; /* reset counts */

setlimittosize(t);

na = numusearray(t, nums); /* count keys in array part */

totaluse = na; /* all those keys are integer keys */

totaluse += numusehash(t, nums, &na); /* count keys in hash part */

/* count extra key */

if (ttisinteger(ek))

na += countint(ivalue(ek), nums);

totaluse++;

/* compute new size for array part */

asize = computesizes(nums, &na);

/* resize the table to new computed sizes */

luaH_resize(L, t, asize, totaluse - na);

}

** }=============================================================

Table *luaH_new (lua_State *L) {

GCObject *o = luaC_newobj(L, LUA_TTABLE, sizeof(Table));

Table *t = gco2t(o);

t->metatable = NULL;

t->flags = cast_byte(~0);

t->array = NULL;

t->alimit = 0;

setnodevector(L, t, 0);

return t;

}

void luaH_free (lua_State *L, Table *t) {

freehash(L, t);

luaM_freearray(L, t->array, luaH_realasize(t));

luaM_free(L, t);

}

static Node *getfreepos (Table *t) {

if (!isdummy(t)) {

while (t->lastfree > t->node) {

t->lastfree--;

if (keyisnil(t->lastfree))

return t->lastfree;

}

return NULL; /* could not find a free place */

}

** inserts a new key into a hash table; first, 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 key in its main position; otherwise (colliding node is in its main

** position), new key goes to an empty position.

TValue *luaH_newkey (lua_State *L, Table *t, const TValue *key) {

Node *mp;

TValue aux;

if (unlikely(ttisnil(key)))

luaG_runerror(L, "table index is nil");

else if (ttisfloat(key)) {

lua_Number f = fltvalue(key);

lua_Integer k;

if (luaV_flttointeger(f, &k, 0)) { /* does key fit in an integer? */

setivalue(&aux, k);

key = &aux; /* insert it as an integer */

}

else if (unlikely(luai_numisnan(f)))

luaG_runerror(L, "table index is NaN");

}

mp = mainpositionTV(t, key);

if (!isempty(gval(mp)) || isdummy(t)) { /* main position is taken? */

Node *othern;

Node *f = getfreepos(t); /* get a free place */

if (f == NULL) { /* cannot find a free place? */

rehash(L, t, key); /* grow table */

/* whatever called 'newkey' takes care of TM cache */

return luaH_set(L, t, key); /* insert key into grown table */

}

lua_assert(!isdummy(t));

othern = mainposition(t, keytt(mp), &keyval(mp));

if (othern != mp) { /* is colliding node out of its main position? */

/* yes; move colliding node into free position */

while (othern + gnext(othern) != mp) /* find previous */

othern += gnext(othern);

gnext(othern) = cast_int(f - othern); /* rechain to point to 'f' */

*f = *mp; /* copy colliding node into free pos. (mp->next also goes) */

if (gnext(mp) != 0) {

gnext(f) += cast_int(mp - f); /* correct 'next' */

gnext(mp) = 0; /* now 'mp' is free */

}

setempty(gval(mp));

}

else { /* colliding node is in its own main position */

/* new node will go into free position */

if (gnext(mp) != 0)

gnext(f) = cast_int((mp + gnext(mp)) - f); /* chain new position */

else lua_assert(gnext(f) == 0);

gnext(mp) = cast_int(f - mp);

mp = f;

}

setnodekey(L, mp, key);

luaC_barrierback(L, obj2gco(t), key);

lua_assert(isempty(gval(mp)));

return gval(mp);

}

** Search function for integers. If integer is inside 'alimit', get it

** directly from the array part. Otherwise, if 'alimit' is not equal to

** the real size of the array, key still can be in the array part. In

** this case, try to avoid a call to 'luaH_realasize' when key is just

** one more than the limit (so that it can be incremented without

** changing the real size of the array).

const TValue *luaH_getint (Table *t, lua_Integer key) {

if (l_castS2U(key) - 1u < t->alimit) /* 'key' in [1, t->alimit]? */

return &t->array[key - 1];

else if (!limitequalsasize(t) && /* key still may be in the array part? */

(l_castS2U(key) == t->alimit + 1 ||

l_castS2U(key) - 1u < luaH_realasize(t))) {

t->alimit = cast_uint(key); /* probably '#t' is here now */

return &t->array[key - 1];

}

else {

Node *n = hashint(t, key);

for (;;) { /* check whether 'key' is somewhere in the chain */

if (keyisinteger(n) && keyival(n) == key)

return gval(n); /* that's it */

else {

int nx = gnext(n);

if (nx == 0) break;

n += nx;

}

return &absentkey;

}

** search function for short strings

const TValue *luaH_getshortstr (Table *t, TString *key) {

Node *n = hashstr(t, key);

lua_assert(key->tt == LUA_TSHRSTR);

for (;;) { /* check whether 'key' is somewhere in the chain */

if (keyisshrstr(n) && eqshrstr(keystrval(n), key))

return gval(n); /* that's it */

else {

int nx = gnext(n);

if (nx == 0)

return &absentkey; /* not found */

n += nx;

}

const TValue *luaH_getstr (Table *t, TString *key) {

if (key->tt == LUA_TSHRSTR)

return luaH_getshortstr(t, key);

else { /* for long strings, use generic case */

TValue ko;

setsvalue(cast(lua_State *, NULL), &ko, key);

return getgeneric(t, &ko);

}

** main search function

const TValue *luaH_get (Table *t, const TValue *key) {

switch (ttypetag(key)) {

case LUA_TSHRSTR: return luaH_getshortstr(t, tsvalue(key));

case LUA_TNUMINT: return luaH_getint(t, ivalue(key));

case LUA_TNIL: return &absentkey;

case LUA_TNUMFLT: {

lua_Integer k;

if (luaV_flttointeger(fltvalue(key), &k, 0)) /* index is an integral? */

return luaH_getint(t, k); /* use specialized version */

/* else... */

} /* FALLTHROUGH */

default:

return getgeneric(t, key);

}

** beware: when using this function you probably need to check a GC

** barrier and invalidate the TM cache.

TValue *luaH_set (lua_State *L, Table *t, const TValue *key) {

const TValue *p = luaH_get(t, key);

if (!isabstkey(p))

return cast(TValue *, p);

else return luaH_newkey(L, t, key);

}

void luaH_setint (lua_State *L, Table *t, lua_Integer key, TValue *value) {

const TValue *p = luaH_getint(t, key);

TValue *cell;

if (!isabstkey(p))

cell = cast(TValue *, p);

else {

TValue k;

setivalue(&k, key);

cell = luaH_newkey(L, t, &k);

}

setobj2t(L, cell, value);

}

** Try to find a boundary in the hash part of table 't'. From the

** caller, we know that 'j' is zero or present and that 'j + 1' is

** present. We want to find a larger key that is absent from the

** table, so that we can do a binary search between the two keys to

** find a boundary. We keep doubling 'j' until we get an absent index.

** If the doubling would overflow, we try LUA_MAXINTEGER. If it is

** absent, we are ready for the binary search. ('j', being max integer,

** is larger or equal to 'i', but it cannot be equal because it is

** absent while 'i' is present; so 'j > i'.) Otherwise, 'j' is a

** boundary. ('j + 1' cannot be a present integer key because it is

** not a valid integer in Lua.)

static lua_Unsigned hash_search (Table *t, lua_Unsigned j) {

lua_Unsigned i;

if (j == 0) j++; /* the caller ensures 'j + 1' is present */

do {

i = j; /* 'i' is a present index */

if (j <= l_castS2U(LUA_MAXINTEGER) / 2)

j *= 2;

else {

j = LUA_MAXINTEGER;

if (isempty(luaH_getint(t, j))) /* t[j] not present? */

break; /* 'j' now is an absent index */

else /* weird case */

return j; /* well, max integer is a boundary... */

}

} while (!isempty(luaH_getint(t, j))); /* repeat until an absent t[j] */

/* i < j && t[i] present && t[j] absent */

while (j - i > 1u) { /* do a binary search between them */

lua_Unsigned m = (i + j) / 2;

if (isempty(luaH_getint(t, m))) j = m;

else i = m;

}

return i;

}

static unsigned int binsearch (const TValue *array, unsigned int i,

unsigned int j) {

while (j - i > 1u) { /* binary search */

unsigned int m = (i + j) / 2;

if (isempty(&array[m - 1])) j = m;

else i = m;

}

return i;

}

** Try to find a boundary in table 't'. (A 'boundary' is an integer index

** such that t[i] is present and t[i+1] is absent, or 0 if t[1] is absent

** and 'maxinteger' if t[maxinteger] is present.)

** (In the next explanation, we use Lua indices, that is, with base 1.

** The code itself uses base 0 when indexing the array part of the table.)

** The code starts with 'limit = t->alimit', a position in the array

** part that may be a boundary.

** (1) If 't[limit]' is empty, there must be a boundary before it.

** As a common case (e.g., after 't[#t]=nil'), check whether 'limit-1'

** is present. If so, it is a boundary. Otherwise, do a binary search

** between 0 and limit to find a boundary. In both cases, try to

** use this boundary as the new 'alimit', as a hint for the next call.

** (2) If 't[limit]' is not empty and the array has more elements

** after 'limit', try to find a boundary there. Again, try first

** the special case (which should be quite frequent) where 'limit+1'

** is empty, so that 'limit' is a boundary. Otherwise, check the

** last element of the array part. If it is empty, there must be a

** boundary between the old limit (present) and the last element

** (absent), which is found with a binary search. (This boundary always

** can be a new limit.)

** (3) The last case is when there are no elements in the array part

** (limit == 0) or its last element (the new limit) is present.

** In this case, must check the hash part. If there is no hash part

** or 'limit+1' is absent, 'limit' is a boundary. Otherwise, call

** 'hash_search' to find a boundary in the hash part of the table.

** (In those cases, the boundary is not inside the array part, and

** therefore cannot be used as a new limit.)

lua_Unsigned luaH_getn (Table *t) {

unsigned int limit = t->alimit;

if (limit > 0 && isempty(&t->array[limit - 1])) { /* (1)? */

/* there must be a boundary before 'limit' */

if (limit >= 2 && !isempty(&t->array[limit - 2])) {

/* 'limit - 1' is a boundary; can it be a new limit? */

if (ispow2realasize(t) && !ispow2(limit - 1)) {

t->alimit = limit - 1;

setnorealasize(t); /* now 'alimit' is not the real size */

}

return limit - 1;

}

else { /* must search for a boundary in [0, limit] */

unsigned int boundary = binsearch(t->array, 0, limit);

/* can this boundary represent the real size of the array? */

if (ispow2realasize(t) && boundary > luaH_realasize(t) / 2) {

t->alimit = boundary; /* use it as the new limit */

setnorealasize(t);

}

return boundary;

}

/* 'limit' is zero or present in table */

if (!limitequalsasize(t)) { /* (2)? */

/* 'limit' > 0 and array has more elements after 'limit' */

if (isempty(&t->array[limit])) /* 'limit + 1' is empty? */

return limit; /* this is the boundary */

/* else, try last element in the array */

limit = luaH_realasize(t);

if (isempty(&t->array[limit - 1])) { /* empty? */

/* there must be a boundary in the array after old limit,

and it must be a valid new limit */

unsigned int boundary = binsearch(t->array, t->alimit, limit);

t->alimit = boundary;

return boundary;

}

/* else, new limit is present in the table; check the hash part */

}

/* (3) 'limit' is the last element and either is zero or present in table */

lua_assert(limit == luaH_realasize(t) &&

(limit == 0 || !isempty(&t->array[limit - 1])));

if (isdummy(t) || isempty(luaH_getint(t, cast(lua_Integer, limit + 1))))

return limit; /* 'limit + 1' is absent */

else /* 'limit + 1' is also present */

return hash_search(t, limit);

}

#if defined(LUA_DEBUG)

/* export these functions for the test library */

Node *luaH_mainposition (const Table *t, const TValue *key) {

return mainpositionTV(t, key);

}

int luaH_isdummy (const Table *t) { return isdummy(t); }

#endif

lua/ltable.c at master · 19as/lua · GitHub

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