1/*
2** $Id: lstring.c $
3** String table (keeps all strings handled by Lua)
4** See Copyright Notice in lua.h
5*/
6
7#define lstring_c
8#define LUA_CORE
9
10#include "lprefix.h"
11
12
13#include <string.h>
14
15#include "lua.h"
16
17#include "ldebug.h"
18#include "ldo.h"
19#include "lmem.h"
20#include "lobject.h"
21#include "lstate.h"
22#include "lstring.h"
23
24
25/*
26** Maximum size for string table.
27*/
28#define MAXSTRTB	cast_int(luaM_limitN(MAX_INT, TString*))
29
30
31/*
32** equality for long strings
33*/
34int luaS_eqlngstr (TString *a, TString *b) {
35  size_t len = a->u.lnglen;
36  lua_assert(a->tt == LUA_VLNGSTR && b->tt == LUA_VLNGSTR);
37  return (a == b) ||  /* same instance or... */
38    ((len == b->u.lnglen) &&  /* equal length and ... */
39     (memcmp(getstr(a), getstr(b), len) == 0));  /* equal contents */
40}
41
42
43unsigned int luaS_hash (const char *str, size_t l, unsigned int seed) {
44  unsigned int h = seed ^ cast_uint(l);
45  for (; l > 0; l--)
46    h ^= ((h<<5) + (h>>2) + cast_byte(str[l - 1]));
47  return h;
48}
49
50
51unsigned int luaS_hashlongstr (TString *ts) {
52  lua_assert(ts->tt == LUA_VLNGSTR);
53  if (ts->extra == 0) {  /* no hash? */
54    size_t len = ts->u.lnglen;
55    ts->hash = luaS_hash(getstr(ts), len, ts->hash);
56    ts->extra = 1;  /* now it has its hash */
57  }
58  return ts->hash;
59}
60
61
62static void tablerehash (TString **vect, int osize, int nsize) {
63  int i;
64  for (i = osize; i < nsize; i++)  /* clear new elements */
65    vect[i] = NULL;
66  for (i = 0; i < osize; i++) {  /* rehash old part of the array */
67    TString *p = vect[i];
68    vect[i] = NULL;
69    while (p) {  /* for each string in the list */
70      TString *hnext = p->u.hnext;  /* save next */
71      unsigned int h = lmod(p->hash, nsize);  /* new position */
72      p->u.hnext = vect[h];  /* chain it into array */
73      vect[h] = p;
74      p = hnext;
75    }
76  }
77}
78
79
80/*
81** Resize the string table. If allocation fails, keep the current size.
82** (This can degrade performance, but any non-zero size should work
83** correctly.)
84*/
85void luaS_resize (lua_State *L, int nsize) {
86  stringtable *tb = &G(L)->strt;
87  int osize = tb->size;
88  TString **newvect;
89  if (nsize < osize)  /* shrinking table? */
90    tablerehash(tb->hash, osize, nsize);  /* depopulate shrinking part */
91  newvect = luaM_reallocvector(L, tb->hash, osize, nsize, TString*);
92  if (l_unlikely(newvect == NULL)) {  /* reallocation failed? */
93    if (nsize < osize)  /* was it shrinking table? */
94      tablerehash(tb->hash, nsize, osize);  /* restore to original size */
95    /* leave table as it was */
96  }
97  else {  /* allocation succeeded */
98    tb->hash = newvect;
99    tb->size = nsize;
100    if (nsize > osize)
101      tablerehash(newvect, osize, nsize);  /* rehash for new size */
102  }
103}
104
105
106/*
107** Clear API string cache. (Entries cannot be empty, so fill them with
108** a non-collectable string.)
109*/
110void luaS_clearcache (global_State *g) {
111  int i, j;
112  for (i = 0; i < STRCACHE_N; i++)
113    for (j = 0; j < STRCACHE_M; j++) {
114      if (iswhite(g->strcache[i][j]))  /* will entry be collected? */
115        g->strcache[i][j] = g->memerrmsg;  /* replace it with something fixed */
116    }
117}
118
119
120/*
121** Initialize the string table and the string cache
122*/
123void luaS_init (lua_State *L) {
124  global_State *g = G(L);
125  int i, j;
126  stringtable *tb = &G(L)->strt;
127  tb->hash = luaM_newvector(L, MINSTRTABSIZE, TString*);
128  tablerehash(tb->hash, 0, MINSTRTABSIZE);  /* clear array */
129  tb->size = MINSTRTABSIZE;
130  /* pre-create memory-error message */
131  g->memerrmsg = luaS_newliteral(L, MEMERRMSG);
132  luaC_fix(L, obj2gco(g->memerrmsg));  /* it should never be collected */
133  for (i = 0; i < STRCACHE_N; i++)  /* fill cache with valid strings */
134    for (j = 0; j < STRCACHE_M; j++)
135      g->strcache[i][j] = g->memerrmsg;
136}
137
138
139
140/*
141** creates a new string object
142*/
143static TString *createstrobj (lua_State *L, size_t l, int tag, unsigned int h) {
144  TString *ts;
145  GCObject *o;
146  size_t totalsize;  /* total size of TString object */
147  totalsize = sizelstring(l);
148  o = luaC_newobj(L, tag, totalsize);
149  ts = gco2ts(o);
150  ts->hash = h;
151  ts->extra = 0;
152  getstr(ts)[l] = '\0';  /* ending 0 */
153  return ts;
154}
155
156
157TString *luaS_createlngstrobj (lua_State *L, size_t l) {
158  TString *ts = createstrobj(L, l, LUA_VLNGSTR, G(L)->seed);
159  ts->u.lnglen = l;
160  return ts;
161}
162
163
164void luaS_remove (lua_State *L, TString *ts) {
165  stringtable *tb = &G(L)->strt;
166  TString **p = &tb->hash[lmod(ts->hash, tb->size)];
167  while (*p != ts)  /* find previous element */
168    p = &(*p)->u.hnext;
169  *p = (*p)->u.hnext;  /* remove element from its list */
170  tb->nuse--;
171}
172
173
174static void growstrtab (lua_State *L, stringtable *tb) {
175  if (l_unlikely(tb->nuse == MAX_INT)) {  /* too many strings? */
176    luaC_fullgc(L, 1);  /* try to free some... */
177    if (tb->nuse == MAX_INT)  /* still too many? */
178      luaM_error(L);  /* cannot even create a message... */
179  }
180  if (tb->size <= MAXSTRTB / 2)  /* can grow string table? */
181    luaS_resize(L, tb->size * 2);
182}
183
184
185/*
186** Checks whether short string exists and reuses it or creates a new one.
187*/
188static TString *internshrstr (lua_State *L, const char *str, size_t l) {
189  TString *ts;
190  global_State *g = G(L);
191  stringtable *tb = &g->strt;
192  unsigned int h = luaS_hash(str, l, g->seed);
193  TString **list = &tb->hash[lmod(h, tb->size)];
194  lua_assert(str != NULL);  /* otherwise 'memcmp'/'memcpy' are undefined */
195  for (ts = *list; ts != NULL; ts = ts->u.hnext) {
196    if (l == ts->shrlen && (memcmp(str, getstr(ts), l * sizeof(char)) == 0)) {
197      /* found! */
198      if (isdead(g, ts))  /* dead (but not collected yet)? */
199        changewhite(ts);  /* resurrect it */
200      return ts;
201    }
202  }
203  /* else must create a new string */
204  if (tb->nuse >= tb->size) {  /* need to grow string table? */
205    growstrtab(L, tb);
206    list = &tb->hash[lmod(h, tb->size)];  /* rehash with new size */
207  }
208  ts = createstrobj(L, l, LUA_VSHRSTR, h);
209  memcpy(getstr(ts), str, l * sizeof(char));
210  ts->shrlen = cast_byte(l);
211  ts->u.hnext = *list;
212  *list = ts;
213  tb->nuse++;
214  return ts;
215}
216
217
218/*
219** new string (with explicit length)
220*/
221TString *luaS_newlstr (lua_State *L, const char *str, size_t l) {
222  if (l <= LUAI_MAXSHORTLEN)  /* short string? */
223    return internshrstr(L, str, l);
224  else {
225    TString *ts;
226    if (l_unlikely(l >= (MAX_SIZE - sizeof(TString))/sizeof(char)))
227      luaM_toobig(L);
228    ts = luaS_createlngstrobj(L, l);
229    memcpy(getstr(ts), str, l * sizeof(char));
230    return ts;
231  }
232}
233
234
235/*
236** Create or reuse a zero-terminated string, first checking in the
237** cache (using the string address as a key). The cache can contain
238** only zero-terminated strings, so it is safe to use 'strcmp' to
239** check hits.
240*/
241TString *luaS_new (lua_State *L, const char *str) {
242  unsigned int i = point2uint(str) % STRCACHE_N;  /* hash */
243  int j;
244  TString **p = G(L)->strcache[i];
245  for (j = 0; j < STRCACHE_M; j++) {
246    if (strcmp(str, getstr(p[j])) == 0)  /* hit? */
247      return p[j];  /* that is it */
248  }
249  /* normal route */
250  for (j = STRCACHE_M - 1; j > 0; j--)
251    p[j] = p[j - 1];  /* move out last element */
252  /* new element is first in the list */
253  p[0] = luaS_newlstr(L, str, strlen(str));
254  return p[0];
255}
256
257
258Udata *luaS_newudata (lua_State *L, size_t s, int nuvalue) {
259  Udata *u;
260  int i;
261  GCObject *o;
262  if (l_unlikely(s > MAX_SIZE - udatamemoffset(nuvalue)))
263    luaM_toobig(L);
264  o = luaC_newobj(L, LUA_VUSERDATA, sizeudata(nuvalue, s));
265  u = gco2u(o);
266  u->len = s;
267  u->nuvalue = nuvalue;
268  u->metatable = NULL;
269  for (i = 0; i < nuvalue; i++)
270    setnilvalue(&u->uv[i].uv);
271  return u;
272}
273
274