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 */
luaS_eqlngstr(TString * a,TString * b)34 int 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(getlngstr(a), getlngstr(b), len) == 0)); /* equal contents */
40 }
41
42
luaS_hash(const char * str,size_t l,unsigned int seed)43 unsigned 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
luaS_hashlongstr(TString * ts)51 unsigned 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(getlngstr(ts), len, ts->hash);
56 ts->extra = 1; /* now it has its hash */
57 }
58 return ts->hash;
59 }
60
61
tablerehash(TString ** vect,int osize,int nsize)62 static 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 */
luaS_resize(lua_State * L,int nsize)85 void 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 */
luaS_clearcache(global_State * g)110 void 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 */
luaS_init(lua_State * L)123 void 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 */
createstrobj(lua_State * L,size_t l,int tag,unsigned int h)143 static 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
luaS_createlngstrobj(lua_State * L,size_t l)157 TString *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 ts->shrlen = 0xFF; /* signals that it is a long string */
161 return ts;
162 }
163
164
luaS_remove(lua_State * L,TString * ts)165 void luaS_remove (lua_State *L, TString *ts) {
166 stringtable *tb = &G(L)->strt;
167 TString **p = &tb->hash[lmod(ts->hash, tb->size)];
168 while (*p != ts) /* find previous element */
169 p = &(*p)->u.hnext;
170 *p = (*p)->u.hnext; /* remove element from its list */
171 tb->nuse--;
172 }
173
174
growstrtab(lua_State * L,stringtable * tb)175 static void growstrtab (lua_State *L, stringtable *tb) {
176 if (l_unlikely(tb->nuse == MAX_INT)) { /* too many strings? */
177 luaC_fullgc(L, 1); /* try to free some... */
178 if (tb->nuse == MAX_INT) /* still too many? */
179 luaM_error(L); /* cannot even create a message... */
180 }
181 if (tb->size <= MAXSTRTB / 2) /* can grow string table? */
182 luaS_resize(L, tb->size * 2);
183 }
184
185
186 /*
187 ** Checks whether short string exists and reuses it or creates a new one.
188 */
internshrstr(lua_State * L,const char * str,size_t l)189 static TString *internshrstr (lua_State *L, const char *str, size_t l) {
190 TString *ts;
191 global_State *g = G(L);
192 stringtable *tb = &g->strt;
193 unsigned int h = luaS_hash(str, l, g->seed);
194 TString **list = &tb->hash[lmod(h, tb->size)];
195 lua_assert(str != NULL); /* otherwise 'memcmp'/'memcpy' are undefined */
196 for (ts = *list; ts != NULL; ts = ts->u.hnext) {
197 if (l == ts->shrlen && (memcmp(str, getshrstr(ts), l * sizeof(char)) == 0)) {
198 /* found! */
199 if (isdead(g, ts)) /* dead (but not collected yet)? */
200 changewhite(ts); /* resurrect it */
201 return ts;
202 }
203 }
204 /* else must create a new string */
205 if (tb->nuse >= tb->size) { /* need to grow string table? */
206 growstrtab(L, tb);
207 list = &tb->hash[lmod(h, tb->size)]; /* rehash with new size */
208 }
209 ts = createstrobj(L, l, LUA_VSHRSTR, h);
210 ts->shrlen = cast_byte(l);
211 memcpy(getshrstr(ts), str, l * sizeof(char));
212 ts->u.hnext = *list;
213 *list = ts;
214 tb->nuse++;
215 return ts;
216 }
217
218
219 /*
220 ** new string (with explicit length)
221 */
luaS_newlstr(lua_State * L,const char * str,size_t l)222 TString *luaS_newlstr (lua_State *L, const char *str, size_t l) {
223 if (l <= LUAI_MAXSHORTLEN) /* short string? */
224 return internshrstr(L, str, l);
225 else {
226 TString *ts;
227 if (l_unlikely(l * sizeof(char) >= (MAX_SIZE - sizeof(TString))))
228 luaM_toobig(L);
229 ts = luaS_createlngstrobj(L, l);
230 memcpy(getlngstr(ts), str, l * sizeof(char));
231 return ts;
232 }
233 }
234
235
236 /*
237 ** Create or reuse a zero-terminated string, first checking in the
238 ** cache (using the string address as a key). The cache can contain
239 ** only zero-terminated strings, so it is safe to use 'strcmp' to
240 ** check hits.
241 */
luaS_new(lua_State * L,const char * str)242 TString *luaS_new (lua_State *L, const char *str) {
243 unsigned int i = point2uint(str) % STRCACHE_N; /* hash */
244 int j;
245 TString **p = G(L)->strcache[i];
246 for (j = 0; j < STRCACHE_M; j++) {
247 if (strcmp(str, getstr(p[j])) == 0) /* hit? */
248 return p[j]; /* that is it */
249 }
250 /* normal route */
251 for (j = STRCACHE_M - 1; j > 0; j--)
252 p[j] = p[j - 1]; /* move out last element */
253 /* new element is first in the list */
254 p[0] = luaS_newlstr(L, str, strlen(str));
255 return p[0];
256 }
257
258
luaS_newudata(lua_State * L,size_t s,int nuvalue)259 Udata *luaS_newudata (lua_State *L, size_t s, int nuvalue) {
260 Udata *u;
261 int i;
262 GCObject *o;
263 if (l_unlikely(s > MAX_SIZE - udatamemoffset(nuvalue)))
264 luaM_toobig(L);
265 o = luaC_newobj(L, LUA_VUSERDATA, sizeudata(nuvalue, s));
266 u = gco2u(o);
267 u->len = s;
268 u->nuvalue = nuvalue;
269 u->metatable = NULL;
270 for (i = 0; i < nuvalue; i++)
271 setnilvalue(&u->uv[i].uv);
272 return u;
273 }
274
275