/*

** $Id: lstring.c $

** 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 "lua.h"

#include "ldebug.h"

#include "ldo.h"

#include "lmem.h"

#include "lobject.h"

#include "lstate.h"

#include "lstring.h"

/*

** Maximum size for string table.

*/

#define MAXSTRTB  cast_int(luaM_limitN(MAX_INT, TString*))

/*

** equality for long strings

*/

int luaS_eqlngstr (TString *a, TString *b) {

  size_t len = a->u.lnglen;

  lua_assert(a->tt == LUA_VLNGSTR && b->tt == LUA_VLNGSTR);

  return (a == b) ||  /* same instance or... */

    ((len == b->u.lnglen) &&  /* equal length and ... */

     (memcmp(getlngstr(a), getlngstr(b), len) == 0));  /* equal contents */

}

unsigned int luaS_hash (const char *str, size_t l, unsigned int seed) {

  unsigned int h = seed ^ cast_uint(l);

  for (; l > 0; l--)

    h ^= ((h<<5) + (h>>2) + cast_byte(str[l - 1]));

  return h;

}

unsigned int luaS_hashlongstr (TString *ts) {

  lua_assert(ts->tt == LUA_VLNGSTR);

  if (ts->extra == 0) {  /* no hash? */

    size_t len = ts->u.lnglen;

    ts->hash = luaS_hash(getlngstr(ts), len, ts->hash);

    ts->extra = 1;  /* now it has its hash */

  }

  return ts->hash;

}

static void tablerehash (TString **vect, int osize, int nsize) {

  int i;

  for (i = osize; i < nsize; i++)  /* clear new elements */

    vect[i] = NULL;

  for (i = 0; i < osize; i++) {  /* rehash old part of the array */

    TString *p = vect[i];

    vect[i] = NULL;

    while (p) {  /* for each string in the list */

      TString *hnext = p->u.hnext;  /* save next */

      unsigned int h = lmod(p->hash, nsize);  /* new position */

      p->u.hnext = vect[h];  /* chain it into array */

      vect[h] = p;

      p = hnext;

    }

  }

}

/*

** Resize the string table. If allocation fails, keep the current size.

** (This can degrade performance, but any non-zero size should work

** correctly.)

*/

void luaS_resize (lua_State *L, int nsize) {

  stringtable *tb = &G(L)->strt;

  int osize = tb->size;

  TString **newvect;

  if (nsize < osize)  /* shrinking table? */

    tablerehash(tb->hash, osize, nsize);  /* depopulate shrinking part */

  newvect = luaM_reallocvector(L, tb->hash, osize, nsize, TString*);

  if (l_unlikely(newvect == NULL)) {  /* reallocation failed? */

    if (nsize < osize)  /* was it shrinking table? */

      tablerehash(tb->hash, nsize, osize);  /* restore to original size */

    /* leave table as it was */

  }

  else {  /* allocation succeeded */

    tb->hash = newvect;

    tb->size = nsize;

    if (nsize > osize)

      tablerehash(newvect, osize, nsize);  /* rehash for new size */

  }

}

/*

** 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;

  stringtable *tb = &G(L)->strt;

  tb->hash = luaM_newvector(L, MINSTRTABSIZE, TString*);

  tablerehash(tb->hash, 0, MINSTRTABSIZE);  /* clear array */

  tb->size = MINSTRTABSIZE;

  /* 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_VLNGSTR, G(L)->seed);

  ts->u.lnglen = l;

  ts->shrlen = 0xFF;  /* signals that it is a long string */

  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--;

}

static void growstrtab (lua_State *L, stringtable *tb) {

  if (l_unlikely(tb->nuse == MAX_INT)) {  /* too many strings? */

    luaC_fullgc(L, 1);  /* try to free some... */

    if (tb->nuse == MAX_INT)  /* still too many? */

      luaM_error(L);  /* cannot even create a message... */

  }

  if (tb->size <= MAXSTRTB / 2)  /* can grow string table? */

    luaS_resize(L, tb->size * 2);

}

/*

** 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);

  stringtable *tb = &g->strt;

  unsigned int h = luaS_hash(str, l, g->seed);

  TString **list = &tb->hash[lmod(h, tb->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, getshrstr(ts), l * sizeof(char)) == 0)) {

      /* found! */

      if (isdead(g, ts))  /* dead (but not collected yet)? */

        changewhite(ts);  /* resurrect it */

      return ts;

    }

  }

  /* else must create a new string */

  if (tb->nuse >= tb->size) {  /* need to grow string table? */

    growstrtab(L, tb);

    list = &tb->hash[lmod(h, tb->size)];  /* rehash with new size */

  }

  ts = createstrobj(L, l, LUA_VSHRSTR, h);

  memcpy(getshrstr(ts), str, l * sizeof(char));

  ts->shrlen = cast_byte(l);

  ts->u.hnext = *list;

  *list = ts;

  tb->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_unlikely(l >= (MAX_SIZE - sizeof(TString))/sizeof(char)))

      luaM_toobig(L);

    ts = luaS_createlngstrobj(L, l);

    memcpy(getlngstr(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, int nuvalue) {

  Udata *u;

  int i;

  GCObject *o;

  if (l_unlikely(s > MAX_SIZE - udatamemoffset(nuvalue)))

    luaM_toobig(L);

  o = luaC_newobj(L, LUA_VUSERDATA, sizeudata(nuvalue, s));

  u = gco2u(o);

  u->len = s;

  u->nuvalue = nuvalue;

  u->metatable = NULL;

  for (i = 0; i < nuvalue; i++)

    setnilvalue(&u->uv[i].uv);

  return u;

}