text: /*
  ** $Id: lstring.c,v 2.56 2015/11/23 11:32:51 roberto Exp $
  ** String table (keeps all strings handled by Lua)
  ** See Copyright Notice in lua.h
  */
  
  #define lstring_c
  #define LUA_CORE
  
  #include "lprefix.h"
  
  
  #include <string.h>
  
  #include "../include/lua.h"
  
  #include "ldebug.h"
  #include "ldo.h"
  #include "lmem.h"
  #include "lobject.h"
  #include "lstate.h"
  #include "lstring.h"
  
  
  #define MEMERRMSG       "not enough memory"
  
  
  /*
  ** Lua will use at most ~(2^LUAI_HASHLIMIT) bytes from a string to
  ** compute its hash
  */
  #if !defined(LUAI_HASHLIMIT)
  #define LUAI_HASHLIMIT		5
  #endif
  
  
  /*
  ** equality for long strings
  */
  int luaS_eqlngstr (TString *a, TString *b) {
    size_t len = a->u.lnglen;
    lua_assert(a->tt == LUA_TLNGSTR && b->tt == LUA_TLNGSTR);
    return (a == b) ||  /* same instance or... */
      ((len == b->u.lnglen) &&  /* equal length and ... */
       (memcmp(getstr(a), getstr(b), len) == 0));  /* equal contents */
  }
  
  
  unsigned int luaS_hash (const char *str, size_t l, unsigned int seed) {
    unsigned int h = seed ^ cast(unsigned int, l);
    size_t step = (l >> LUAI_HASHLIMIT) + 1;
    for (; l >= step; l -= step)
      h ^= ((h<<5) + (h>>2) + cast_byte(str[l - 1]));
    return h;
  }
  
  
  unsigned int luaS_hashlongstr (TString *ts) {
    lua_assert(ts->tt == LUA_TLNGSTR);
    if (ts->extra == 0) {  /* no hash? */
      ts->hash = luaS_hash(getstr(ts), ts->u.lnglen, ts->hash);
      ts->extra = 1;  /* now it has its hash */
    }
    return ts->hash;
  }
  
  
  /*
  ** resizes the string table
  */
  void luaS_resize (lua_State *L, int newsize) {
    int i;
    stringtable *tb = &G(L)->strt;
    if (newsize > tb->size) {  /* grow table if needed */
      luaM_reallocvector(L, tb->hash, tb->size, newsize, TString *);
      for (i = tb->size; i < newsize; i++)
        tb->hash[i] = NULL;
    }
    for (i = 0; i < tb->size; i++) {  /* rehash */
      TString *p = tb->hash[i];
      tb->hash[i] = NULL;
      while (p) {  /* for each node in the list */
        TString *hnext = p->u.hnext;  /* save next */
        unsigned int h = lmod(p->hash, newsize);  /* new position */
        p->u.hnext = tb->hash[h];  /* chain it */
        tb->hash[h] = p;
        p = hnext;
      }
    }
    if (newsize < tb->size) {  /* shrink table if needed */
      /* vanishing slice should be empty */
      lua_assert(tb->hash[newsize] == NULL && tb->hash[tb->size - 1] == NULL);
      luaM_reallocvector(L, tb->hash, tb->size, newsize, TString *);
    }
    tb->size = newsize;
  }
  
  
  /*
  ** Clear API string cache. (Entries cannot be empty, so fill them with
  ** a non-collectable string.)
  */
  void luaS_clearcache (global_State *g) {
    int i, j;
    for (i = 0; i < STRCACHE_N; i++)
      for (j = 0; j < STRCACHE_M; j++) {
      if (iswhite(g->strcache[i][j]))  /* will entry be collected? */
        g->strcache[i][j] = g->memerrmsg;  /* replace it with something fixed */
      }
  }
  
  
  /*
  ** Initialize the string table and the string cache
  */
  void luaS_init (lua_State *L) {
    global_State *g = G(L);
    int i, j;
    luaS_resize(L, MINSTRTABSIZE);  /* initial size of string table */
    /* pre-create memory-error message */
    g->memerrmsg = luaS_newliteral(L, MEMERRMSG);
    luaC_fix(L, obj2gco(g->memerrmsg));  /* it should never be collected */
    for (i = 0; i < STRCACHE_N; i++)  /* fill cache with valid strings */
      for (j = 0; j < STRCACHE_M; j++)
        g->strcache[i][j] = g->memerrmsg;
  }
  
  
  
  /*
  ** creates a new string object
  */
  static TString *createstrobj (lua_State *L, size_t l, int tag, unsigned int h) {
    TString *ts;
    GCObject *o;
    size_t totalsize;  /* total size of TString object */
    totalsize = sizelstring(l);
    o = luaC_newobj(L, tag, totalsize);
    ts = gco2ts(o);
    ts->hash = h;
    ts->extra = 0;
    getstr(ts)[l] = '\0';  /* ending 0 */
    return ts;
  }
  
  
  TString *luaS_createlngstrobj (lua_State *L, size_t l) {
    TString *ts = createstrobj(L, l, LUA_TLNGSTR, G(L)->seed);
    ts->u.lnglen = l;
    return ts;
  }
  
  
  void luaS_remove (lua_State *L, TString *ts) {
    stringtable *tb = &G(L)->strt;
    TString **p = &tb->hash[lmod(ts->hash, tb->size)];
    while (*p != ts)  /* find previous element */
      p = &(*p)->u.hnext;
    *p = (*p)->u.hnext;  /* remove element from its list */
    tb->nuse--;
  }
  
  
  /*
  ** checks whether short string exists and reuses it or creates a new one
  */
  static TString *internshrstr (lua_State *L, const char *str, size_t l) {
    TString *ts;
    global_State *g = G(L);
    unsigned int h = luaS_hash(str, l, g->seed);
    TString **list = &g->strt.hash[lmod(h, g->strt.size)];
    lua_assert(str != NULL);  /* otherwise 'memcmp'/'memcpy' are undefined */
    for (ts = *list; ts != NULL; ts = ts->u.hnext) {
      if (l == ts->shrlen &&
          (memcmp(str, getstr(ts), l * sizeof(char)) == 0)) {
        /* found! */
        if (isdead(g, ts))  /* dead (but not collected yet)? */
          changewhite(ts);  /* resurrect it */
        return ts;
      }
    }
    if (g->strt.nuse >= g->strt.size && g->strt.size <= MAX_INT/2) {
      luaS_resize(L, g->strt.size * 2);
      list = &g->strt.hash[lmod(h, g->strt.size)];  /* recompute with new size */
    }
    ts = createstrobj(L, l, LUA_TSHRSTR, h);
    memcpy(getstr(ts), str, l * sizeof(char));
    ts->shrlen = cast_byte(l);
    ts->u.hnext = *list;
    *list = ts;
    g->strt.nuse++;
    return ts;
  }
  
  
  /*
  ** new string (with explicit length)
  */
  TString *luaS_newlstr (lua_State *L, const char *str, size_t l) {
    if (l <= LUAI_MAXSHORTLEN)  /* short string? */
      return internshrstr(L, str, l);
    else {
      TString *ts;
      if (l >= (MAX_SIZE - sizeof(TString))/sizeof(char))
        luaM_toobig(L);
      ts = luaS_createlngstrobj(L, l);
      memcpy(getstr(ts), str, l * sizeof(char));
      return ts;
    }
  }
  
  
  /*
  ** Create or reuse a zero-terminated string, first checking in the
  ** cache (using the string address as a key). The cache can contain
  ** only zero-terminated strings, so it is safe to use 'strcmp' to
  ** check hits.
  */
  TString *luaS_new (lua_State *L, const char *str) {
    unsigned int i = point2uint(str) % STRCACHE_N;  /* hash */
    int j;
    TString **p = G(L)->strcache[i];
    for (j = 0; j < STRCACHE_M; j++) {
      if (strcmp(str, getstr(p[j])) == 0)  /* hit? */
        return p[j];  /* that is it */
    }
    /* normal route */
    for (j = STRCACHE_M - 1; j > 0; j--)
      p[j] = p[j - 1];  /* move out last element */
    /* new element is first in the list */
    p[0] = luaS_newlstr(L, str, strlen(str));
    return p[0];
  }
  
  
  Udata *luaS_newudata (lua_State *L, size_t s) {
    Udata *u;
    GCObject *o;
    if (s > MAX_SIZE - sizeof(Udata))
      luaM_toobig(L);
    o = luaC_newobj(L, LUA_TUSERDATA, sizeludata(s));
    u = gco2u(o);
    u->len = s;
    u->metatable = NULL;
    setuservalue(L, u, luaO_nilobject);
    return u;
  }
  
  