nodemcu-firmware/app/lua/ltable.c

/*
** $Id: ltable.c,v 2.32.1.2 2007/12/28 15:32:23 roberto Exp $
** Lua tables (hash)
** See Copyright Notice in lua.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 at
** least half the slots between 0 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.
*/

#define ltable_c
#define LUA_CORE

#include "lua.h"
#include <math.h>
#include <string.h>

#include "ldebug.h"
#include "ldo.h"
#include "lgc.h"
#include "lmem.h"
#include "lobject.h"
#include "lstate.h"
#include "ltable.h"
#include "lstring.h"


/*
** max size of array part is 2^MAXBITS
*/
#if LUAI_BITSINT > 26
#define MAXBITS		26
#else
#define MAXBITS		(LUAI_BITSINT-2)
#endif

#define MAXASIZE	(1 << MAXBITS)


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

#define hashstr(t,str)  hashpow2(t, (str)->tsv.hash)
#define hashboolean(t,p)        hashpow2(t, p)


/*
** 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, IntPoint(p))


/*
** number of ints inside a lua_Number
*/
#define numints		cast_int(sizeof(lua_Number)/sizeof(int))

static const TValue* rotable_findentry(ROTable *rotable, TString *key, unsigned *ppos);
static void rotable_next_helper(lua_State *L, ROTable *pentries, int pos,
                             TValue *key, TValue *val);
static void rotable_next(lua_State *L, ROTable *rotable, TValue *key, TValue *val);


#define dummynode		(&dummynode_)

static const Node dummynode_ = {
  {LUA_TVALUE_NIL},  /* value */
  {LUA_TKEY_NIL}     /* key */
};


/*
** hash for lua_Numbers
*/
static Node *hashnum (const Table *t, lua_Number n) {
  unsigned int a[numints];
  int i;
  if (luai_numeq(n, 0))  /* avoid problems with -0 */
    return gnode(t, 0);
  memcpy(a, &n, sizeof(a));
  for (i = 1; i < numints; i++) a[0] += a[i];
  return hashmod(t, a[0]);
}



/*
** returns the `main' position of an element in a table (that is, the index
** of its hash value)
*/
static Node *mainposition (const Table *t, const TValue *key) {
  switch (ttype(key)) {
    case LUA_TNUMBER:
      return hashnum(t, nvalue(key));
    case LUA_TSTRING:
      return hashstr(t, rawtsvalue(key));
    case LUA_TBOOLEAN:
      return hashboolean(t, bvalue(key));
    case LUA_TLIGHTUSERDATA:
    case LUA_TLIGHTFUNCTION:
      return hashpointer(t, pvalue(key));
    case LUA_TROTABLE:
      return hashpointer(t, hvalue(key));
    default:
      return hashpointer(t, gcvalue(key));
  }
}


/*
** returns the index for `key' if `key' is an appropriate key to live in
** the array part of the table, -1 otherwise.
*/
static int arrayindex (const TValue *key) {
  if (ttisnumber(key)) {
    lua_Number n = nvalue(key);
    int k;
    lua_number2int(k, n);
    if (luai_numeq(cast_num(k), n))
      return k;
  }
  return -1;  /* `key' did not match some condition */
}


/*
** 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 signalled by -1.
*/
static int findindex (lua_State *L, Table *t, StkId key) {
  int i;
  if (ttisnil(key)) return -1;  /* first iteration */
  i = arrayindex(key);
  if (0 < i && i <= t->sizearray)  /* is `key' inside array part? */
    return i-1;  /* yes; that's the index (corrected to C) */
  else {
    Node *n = mainposition(t, key);
    do {  /* check whether `key' is somewhere in the chain */
      /* key may be dead already, but it is ok to use it in `next' */
      if (luaO_rawequalObj(key2tval(n), key) ||
            (ttype(gkey(n)) == LUA_TDEADKEY && iscollectable(key) &&
             gcvalue(gkey(n)) == gcvalue(key))) {
        i = cast_int(n - gnode(t, 0));  /* key index in hash table */
        /* hash elements are numbered after array ones */
        return i + t->sizearray;
      }
      else n = gnext(n);
    } while (n);
    luaG_runerror(L, "invalid key to " LUA_QL("next"));  /* key not found */
    return 0;  /* to avoid warnings */
  }
}


int luaH_next (lua_State *L, Table *t, StkId key) {
  int i;
  if (isrotable(t)) {
    rotable_next(L, (ROTable *) t, key, key+1);
    return ttisnil(key) ? 0 : 1;
  }
  i = findindex(L, t, key);  /* find original element */
  for (i++; i < t->sizearray; i++) {  /* try first array part */
    if (!ttisnil(&t->array[i])) {  /* a non-nil value? */
      setnvalue(key, cast_num(i+1));
      setobj2s(L, key+1, &t->array[i]);
      return 1;
    }
  }
  for (i -= t->sizearray; i < sizenode(t); i++) {  /* then hash part */
    if (!ttisnil(gval(gnode(t, i)))) {  /* a non-nil value? */
      setobj2s(L, key, key2tval(gnode(t, i)));
      setobj2s(L, key+1, gval(gnode(t, i)));
      return 1;
    }
  }
  return 0;  /* no more elements */
}


/*
** {=============================================================
** Rehash
** ==============================================================
*/


static int computesizes (int nums[], int *narray) {
  int i;
  int twotoi;  /* 2^i */
  int a = 0;  /* number of elements smaller than 2^i */
  int na = 0;  /* number of elements to go to array part */
  int n = 0;  /* optimal size for array part */
  for (i = 0, twotoi = 1; twotoi/2 < *narray; i++, twotoi *= 2) {
    if (nums[i] > 0) {
      a += nums[i];
      if (a > twotoi/2) {  /* more than half elements present? */
        n = twotoi;  /* optimal size (till now) */
        na = a;  /* all elements smaller than n will go to array part */
      }
    }
    if (a == *narray) break;  /* all elements already counted */
  }
  *narray = n;
  lua_assert(*narray/2 <= na && na <= *narray);
  return na;
}


static int countint (const TValue *key, int *nums) {
  int k = arrayindex(key);
  if (0 < k && k <= MAXASIZE) {  /* is `key' an appropriate array index? */
    nums[ceillog2(k)]++;  /* count as such */
    return 1;
  }
  else
    return 0;
}


static int numusearray (const Table *t, int *nums) {
  int lg;
  int ttlg;  /* 2^lg */
  int ause = 0;  /* summation of `nums' */
  int i = 1;  /* count to traverse all array keys */
  for (lg=0, ttlg=1; lg<=MAXBITS; lg++, ttlg*=2) {  /* for each slice */
    int lc = 0;  /* counter */
    int lim = ttlg;
    if (lim > t->sizearray) {
      lim = t->sizearray;  /* 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 (!ttisnil(&t->array[i-1]))
        lc++;
    }
    nums[lg] += lc;
    ause += lc;
  }
  return ause;
}


static int numusehash (const Table *t, int *nums, int *pnasize) {
  int totaluse = 0;  /* total number of elements */
  int ause = 0;  /* summation of `nums' */
  int i = sizenode(t);
  while (i--) {
    Node *n = &t->node[i];
    if (!ttisnil(gval(n))) {
      ause += countint(key2tval(n), nums);
      totaluse++;
    }
  }
  *pnasize += ause;
  return totaluse;
}


static void setarrayvector (lua_State *L, Table *t, int size) {
  int i;
  luaM_reallocvector(L, t->array, t->sizearray, size, TValue);
  for (i=t->sizearray; i<size; i++)
     setnilvalue(&t->array[i]);
  t->sizearray = size;
}


static Node *getfreepos (Table *t) {
  while (t->lastfree-- > t->node) {
    if (ttisnil(gkey(t->lastfree)))
      return t->lastfree;
  }
  return NULL;  /* could not find a free place */
}


static void resizenodevector (lua_State *L, Table *t, int oldsize, int newsize) {
  int lsize;
  if (newsize == 0) {  /* no elements to hash part? */
    t->node = cast(Node *, dummynode);  /* use common `dummynode' */
    lsize = 0;
  }
  else {
    Node *node = t->node;
    int i;
    lsize = ceillog2(newsize);
    if (lsize > MAXBITS)
      luaG_runerror(L, "table overflow");
    newsize = twoto(lsize);
    if (node == dummynode) {
      oldsize = 0;
      node = NULL; /* don't try to realloc `dummynode' pointer. */
    }
    luaM_reallocvector(L, node, oldsize, newsize, Node);
    t->node = node;
    for (i=oldsize; i<newsize; i++) {
      Node *n = gnode(t, i);
      gnext(n) = NULL;
      setnilvalue(gkey(n));
      setnilvalue(gval(n));
    }
  }
  t->lsizenode = cast_byte(lsize);
  t->lastfree = gnode(t, newsize);  /* reset lastfree to end of table. */
}


static Node *find_prev_node(Node *mp, Node *next) {
  Node *prev = mp;
  while (prev != NULL && gnext(prev) != next) prev = gnext(prev);
  return prev;
}


/*
** move a node from it's old position to it's new position during a rehash;
** first, check whether the moving node'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 moving node in its main position; otherwise
** (colliding node is in its main position), moving node goes to an empty position.
*/
static int move_node (lua_State *L, Table *t, Node *node) {
  Node *mp = mainposition(t, key2tval(node));
  /* if node is in it's main position, don't need to move node. */
  if (mp == node) return 1;
  /* if node is in it's main position's chain, don't need to move node. */
  if (find_prev_node(mp, node) != NULL) return 1;
  /* is main position is free? */
  if (!ttisnil(gval(mp)) || mp == dummynode) {
    /* no; move main position node if it is out of its main position */
    Node *othermp;
    othermp = mainposition(t, key2tval(mp));
    if (othermp != mp) {  /* is colliding node out of its main position? */
      /* yes; swap colliding node with the node that is being moved. */
      Node *prev;
      Node tmp;
      tmp = *node;
      prev = find_prev_node(othermp, mp);  /* find previous */
      if (prev != NULL) gnext(prev) = node;  /* redo the chain with `n' in place of `mp' */
      *node = *mp;  /* copy colliding node into free pos. (mp->next also goes) */
      *mp = tmp;
      return (prev != NULL) ? 1 : 0; /* is colliding node part of its main position chain? */
    }
    else {  /* colliding node is in its own main position */
      /* add node to main position's chain. */
      gnext(node) = gnext(mp);  /* chain new position */
      gnext(mp) = node;
    }
  }
  else { /* main position is free, move node */
    *mp = *node;
    gnext(node) = NULL;
    setnilvalue(gkey(node));
    setnilvalue(gval(node));
  }
  return 1;
}


static int move_number (lua_State *L, Table *t, Node *node) {
  int key;
  lua_Number n = nvalue(key2tval(node));
  lua_number2int(key, n);
  if (luai_numeq(cast_num(key), nvalue(key2tval(node)))) {/* index is int? */
    /* (1 <= key && key <= t->sizearray) */
    if (cast(unsigned int, key-1) < cast(unsigned int, t->sizearray)) {
      setobjt2t(L, &t->array[key-1], gval(node));
      setnilvalue(gkey(node));
      setnilvalue(gval(node));
      return 1;
    }
  }
  return 0;
}


static void resize_hashpart (lua_State *L, Table *t, int nhsize) {
  int i;
  int lsize=0;
  int oldhsize = (t->node != dummynode) ? twoto(t->lsizenode) : 0;
  if (nhsize > 0) { /* round new hashpart size up to next power of two. */
    lsize=ceillog2(nhsize);
    if (lsize > MAXBITS)
      luaG_runerror(L, "table overflow");
  }
  nhsize = twoto(lsize);
  /* grow hash part to new size. */
  if (oldhsize < nhsize)
    resizenodevector(L, t, oldhsize, nhsize);
  else { /* hash part might be shrinking */
    if (nhsize > 0) {
      t->lsizenode = cast_byte(lsize);
      t->lastfree = gnode(t, nhsize);  /* reset lastfree back to end of table. */
    }
    else { /* new hashpart size is zero. */
      resizenodevector(L, t, oldhsize, nhsize);
      return;
    }
  }
  /* break old chains, try moving int keys to array part and compact keys into new hashpart */
  for (i = 0; i < oldhsize; i++) {
    Node *old = gnode(t, i);
    gnext(old) = NULL;
    if (ttisnil(gval(old))) { /* clear nodes with nil values. */
      setnilvalue(gkey(old));
      continue;
    }
    if (ttisnumber(key2tval(old))) { /* try moving the int keys into array part. */
      if(move_number(L, t, old))
        continue;
    }
    if (i >= nhsize) { /* move all valid keys to indices < nhsize. */
      Node *n = getfreepos(t);  /* get a free place */
      lua_assert(n != dummynode && n != NULL);
      *n = *old;
    }
  }
  /* shrink hash part */
  if (oldhsize > nhsize)
    resizenodevector(L, t, oldhsize, nhsize);
  /* move nodes to their new mainposition and re-create node chains */
  for (i = 0; i < nhsize; i++) {
    Node *curr = gnode(t, i);
    if (!ttisnil(gval(curr)))
      while (move_node(L, t, curr) == 0);
  }
}


static void resize (lua_State *L, Table *t, int nasize, int nhsize) {
  int i;
  int oldasize = t->sizearray;
  if (nasize > oldasize)  /* array part must grow? */
    setarrayvector(L, t, nasize);
  if (t->node != dummynode || nhsize>0)
    resize_hashpart(L, t, nhsize);
  if (nasize < oldasize) {  /* array part must shrink? */
    t->sizearray = nasize;
    /* re-insert elements from vanishing slice */
    for (i=nasize; i<oldasize; i++) {
      if (!ttisnil(&t->array[i]))
        setobjt2t(L, luaH_setnum(L, t, i+1), &t->array[i]);
    }
    /* shrink array */
    luaM_reallocvector(L, t->array, oldasize, nasize, TValue);
  }
}


void luaH_resizearray (lua_State *L, Table *t, int nasize) {
  int nsize = (t->node == dummynode) ? 0 : sizenode(t);
  resize(L, t, nasize, nsize);
}


static void rehash (lua_State *L, Table *t, const TValue *ek) {
  int nasize, na;
  int nums[MAXBITS+1];  /* nums[i] = number of keys between 2^(i-1) and 2^i */
  int i;
  int totaluse;
  for (i=0; i<=MAXBITS; i++) nums[i] = 0;  /* reset counts */
  nasize = numusearray(t, nums);  /* count keys in array part */
  totaluse = nasize;  /* all those keys are integer keys */
  totaluse += numusehash(t, nums, &nasize);  /* count keys in hash part */
  /* count extra key */
  nasize += countint(ek, nums);
  totaluse++;
  /* compute new size for array part */
  na = computesizes(nums, &nasize);
  /* resize the table to new computed sizes */
  resize(L, t, nasize, totaluse - na);
}



/*
** }=============================================================
*/


Table *luaH_new (lua_State *L, int narray, int nhash) {
  Table *t = luaM_new(L, Table);
  luaC_link(L, obj2gco(t), LUA_TTABLE);
  sethvalue2s(L, L->top, t); /* put table on stack */
  incr_top(L);
  t->metatable = NULL;
  t->flags = cast_byte(~0);
  /* temporary values (kept only if some malloc fails) */
  t->array = NULL;
  t->sizearray = 0;
  t->lsizenode = 0;
  t->node = cast(Node *, dummynode);
  setarrayvector(L, t, narray);
  resizenodevector(L, t, 0, nhash);
  L->top--; /* remove table from stack */
  return t;
}


void luaH_free (lua_State *L, Table *t) {
  if (t->node != dummynode)
    luaM_freearray(L, t->node, sizenode(t), Node);
  luaM_freearray(L, t->array, t->sizearray, TValue);
  luaM_free(L, t);
}



/*
** 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.
*/
static TValue *newkey (lua_State *L, Table *t, const TValue *key) {
  Node *mp = mainposition(t, key);
  if (!ttisnil(gval(mp)) || mp == dummynode) {
    Node *othern;
    Node *n = getfreepos(t);  /* get a free place */
    if (n == NULL) {  /* cannot find a free place? */
      rehash(L, t, key);  /* grow table */
      return luaH_set(L, t, key);  /* re-insert key into grown table */
    }
    lua_assert(n != dummynode);
    othern = mainposition(t, key2tval(mp));
    if (othern != mp) {  /* is colliding node out of its main position? */
      /* yes; move colliding node into free position */
      while (gnext(othern) != mp) othern = gnext(othern);  /* find previous */
      gnext(othern) = n;  /* redo the chain with `n' in place of `mp' */
      *n = *mp;  /* copy colliding node into free pos. (mp->next also goes) */
      gnext(mp) = NULL;  /* now `mp' is free */
      setnilvalue(gval(mp));
    }
    else {  /* colliding node is in its own main position */
      /* new node will go into free position */
      gnext(n) = gnext(mp);  /* chain new position */
      gnext(mp) = n;
      mp = n;
    }
  }
  setobj2t(L, gkey(mp), key);
  luaC_barriert(L, t, key);
  lua_assert(ttisnil(gval(mp)));
  return gval(mp);
}


/*
** search function for integers
*/
const TValue *luaH_getnum (Table *t, int key) {
  if (isrotable(t))
    return luaO_nilobject;
  /* (1 <= key && key <= t->sizearray) */
  if (cast(unsigned int, key-1) < cast(unsigned int, t->sizearray))
    return &t->array[key-1];
  else {
    lua_Number nk = cast_num(key);
    Node *n = hashnum(t, nk);
    do {  /* check whether `key' is somewhere in the chain */
      if (ttisnumber(gkey(n)) && luai_numeq(nvalue(gkey(n)), nk))
        return gval(n);  /* that's it */
      else n = gnext(n);
    } while (n);
    return luaO_nilobject;
  }
}

/*
** search function for strings
*/
const TValue *luaH_getstr (Table *t, TString *key) {

  if (isrotable(t)) {
    if (key->tsv.len>LUA_MAX_ROTABLE_NAME)
      return luaO_nilobject;
    return rotable_findentry((ROTable*) t, key, NULL);
  }
  Node *n = hashstr(t, key);
  do {  /* check whether `key' is somewhere in the chain */
    if (ttisstring(gkey(n)) && rawtsvalue(gkey(n)) == key)
      return gval(n);  /* that's it */
    else n = gnext(n);
  } while (n);
  return luaO_nilobject;
}


/*
** main search function
*/
const TValue *luaH_get (Table *t, const TValue *key) {
  int type = ttype(key);
  if (type == LUA_TNIL)
    return luaO_nilobject;
  if (type == LUA_TSTRING)
    return luaH_getstr(t, rawtsvalue(key));
  if (isrotable(t))
    return luaO_nilobject;
  if (type == LUA_TNUMBER) {
    int k;
    lua_Number n = nvalue(key);
    lua_number2int(k, n);
    if (luai_numeq(cast_num(k), nvalue(key))) /* index is int? */
      return luaH_getnum(t, k);  /* use specialized version */
  }
  /* default */
  Node *n = mainposition(t, key);
  do {  /* check whether `key' is somewhere in the chain */
    if (luaO_rawequalObj(key2tval(n), key))
      return gval(n);  /* that's it */
    else n = gnext(n);
  } while (n);
  return luaO_nilobject;
}


TValue *luaH_set (lua_State *L, Table *t, const TValue *key) {
  const TValue *p;
  if (isrotable(t))
    luaG_runerror(L, "table is readonly");
  p  = luaH_get(t, key);
  t->flags = 0;
  if (p != luaO_nilobject)
    return cast(TValue *, p);
  else {
    if (ttisnil(key)) luaG_runerror(L, "table index is nil");
    else if (ttisnumber(key) && luai_numisnan(nvalue(key)))
      luaG_runerror(L, "table index is NaN");
    return newkey(L, t, key);
  }
}


TValue *luaH_setnum (lua_State *L, Table *t, int key) {
  const TValue *p;
  if (isrotable(t))
    luaG_runerror(L, "table is readonly");
  p = luaH_getnum(t, key);
  if (p != luaO_nilobject)
    return cast(TValue *, p);
  else {
    TValue k;
    setnvalue(&k, cast_num(key));
    return newkey(L, t, &k);
  }
}


TValue *luaH_setstr (lua_State *L, Table *t, TString *key) {
  const TValue *p;
  if (isrotable(t))
    luaG_runerror(L, "table is readonly");
  p  = luaH_getstr(t, key);
  if (p != luaO_nilobject)
    return cast(TValue *, p);
  else {
    TValue k;
    setsvalue(L, &k, key);
    return newkey(L, t, &k);
  }
}


static int unbound_search (Table *t, unsigned int j) {
  unsigned int i = j;  /* i is zero or a present index */
  j++;
  /* find `i' and `j' such that i is present and j is not */
  while (!ttisnil(luaH_getnum(t, j))) {
    i = j;
    j *= 2;
    if (j > cast(unsigned int, MAX_INT)) {  /* overflow? */
      /* table was built with bad purposes: resort to linear search */
      i = 1;
      while (!ttisnil(luaH_getnum(t, i))) i++;
      return i - 1;
    }
  }
  /* now do a binary search between them */
  while (j - i > 1) {
    unsigned int m = (i+j)/2;
    if (ttisnil(luaH_getnum(t, m))) 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 non-nil and t[i+1] is nil (and 0 if t[1] is nil).
*/
int luaH_getn (Table *t) {
  unsigned int j;
  if(isrotable(t))
    return 0;
  j = t->sizearray;
  if (j > 0 && ttisnil(&t->array[j - 1])) {
    /* there is a boundary in the array part: (binary) search for it */
    unsigned int i = 0;
    while (j - i > 1) {
      unsigned int m = (i+j)/2;
      if (ttisnil(&t->array[m - 1])) j = m;
      else i = m;
    }
    return i;
  }
  /* else must find a boundary in hash part */
  else if (t->node == dummynode)  /* hash part is empty? */
    return j;  /* that is easy... */
  else return unbound_search(t, j);
}


int luaH_isdummy (Node *n) { return n == dummynode; }


/*
** All keyed ROTable access passes through rotable_findentry().  ROTables
** are simply a list of <key><TValue value> pairs.
**
** The global KeyCache is used to avoid a relatively expensive Flash memory
** vector scan.  A simple hash on the key's TString addr and the ROTable
** addr selects the cache line.  The line's slots are then scanned for a
** hit.
**
** Unlike the standard hast which uses a prime line count therefore requires
** the use of modulus operation which is expensive on an IoT processor
** without H/W divide.  This hash is power of 2 based which might not be
** quite so uniform but can be calcuated without using H/W-based instructions.
**
** If a match is found and the table addresses match, then this entry is
** probed first. In practice the hit-rate here is over 99% so the code
** rarely fails back to doing the linear scan in ROM.
** Note that this hash does a couple of prime multiples and a modulus 2^X
** with is all evaluated in H/W, and adequately randomizes the lookup.
*/
#define LA_LINES 32
#define LA_SLOTS 4
static size_t cache [LA_LINES][LA_SLOTS];

#define HASH(a,b) ((((29*(size_t)(a)) ^ (37*((b)->tsv.hash)))>>4) % LA_LINES)
#define NDX_SHFT 24
#define ADDR_MASK (((size_t) 1<<24)-1)

/*
 * Find a string key entry in a rotable and return it.  Note that this internally
 * uses a null key to denote a metatable search.
 */
static const TValue* rotable_findentry(ROTable *t, TString *key, unsigned *ppos) {
  const ROTable_entry *e = cast(const ROTable_entry *, t->entry);
  const int tl = getlsizenode(t);
  const char *strkey = getstr(key);
  size_t *cl = cache[HASH(t, key)];
  int i, j = 1, l;

  if (!e || gettt(key) != LUA_TSTRING)
    return luaO_nilobject;

  l = key->tsv.len;
  /* scan the ROTable lookaside cache and return if hit found */
  for (i=0; i<LA_SLOTS; i++) {
    int cl_ndx = cl[i] >> NDX_SHFT;
    if ((((size_t)t - cl[i]) & ADDR_MASK) == 0 && cl_ndx < tl &&
        strcmp(e[cl_ndx].key, strkey) == 0) {
       if (ppos)
          *ppos = cl_ndx;
      return &e[cl_ndx].value;
    }
  }

 /*
  * A lot of search misses are metavalues, but tables typically only have at
  * most a couple of them, so these are always put at the front of the table
  * in ascending order and the metavalue scan short circuits using a straight
  * strcmp()
  */
  lu_int32 name4 = *(lu_int32 *) strkey;
  if (*(char*)&name4  == '_') {
    for(i = 0; i < tl; i++) {
      j = strcmp(e[i].key, strkey);
      if (j>=0)
        break;
    }
  } else {
 /*
  * Ordinary (non-meta) keys can be unsorted.  This is for legacy compatiblity,
  * plus misses are pretty rare in this case.  The masked name4 comparison is
  * safe 4-byte comparison that nearly always avoids the more costly strcmp()
  * for an actual hit validation.
  */
    lu_int32 mask4 = l > 2 ? (~0u) : (~0u)>>((3-l)*8);
    for(i = 0; i < tl; i++) {
      if (((*(lu_int32 *)e[i].key ^ name4) & mask4) != 0)
        continue;
      j = strcmp(e[i].key, strkey);
      if (j==0)
        break;
    }
  }
  if (j)
    return luaO_nilobject;
  if (ppos)
    *ppos = i;
  /* In the case of a hit, update the lookaside cache */
  for (j = LA_SLOTS-1; j>0; j--)
    cl[j] = cl[j-1];
  cl[0] = ((size_t)t & ADDR_MASK) + (i << NDX_SHFT);
  return &e[i].value;
}


static void rotable_next_helper(lua_State *L, ROTable *t, int pos,
                             TValue *key, TValue *val) {
  const ROTable_entry *e = cast(const ROTable_entry *, t->entry);
  if (pos < getlsizenode(t)) {
    /* Found an entry */
    setsvalue(L, key, luaS_new(L, e[pos].key));
    setobj2s(L, val, &e[pos].value);
  } else {
    setnilvalue(key);
    setnilvalue(val);
  }
}


/* next (used for iteration) */
static void rotable_next(lua_State *L, ROTable *t, TValue *key, TValue *val) {
  unsigned keypos = getlsizenode(t);

  /* Special case: if key is nil, return the first element of the rotable */
  if (ttisnil(key))
    rotable_next_helper(L, t, 0, key, val);
  else if (ttisstring(key)) {
    /* Find the previous key again */
    if (ttisstring(key)) {
      rotable_findentry(t, rawtsvalue(key), &keypos);
    }
    /* Advance to next key */
    rotable_next_helper(L, t, ++keypos, key, val);
  }
}



#if defined(LUA_DEBUG)
Node *luaH_mainposition (const Table *t, const TValue *key) {
  return mainposition(t, key);
}
#endif