1 /*
2 ** $Id: lstring.c,v 2.56.1.1 2017/04/19 17:20:42 roberto Exp $
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 #define MEMERRMSG "not enough memory"
26
27
28 /*
29 ** Lua will use at most ~(2^LUAI_HASHLIMIT) bytes from a string to
30 ** compute its hash
31 */
32 #if !defined(LUAI_HASHLIMIT)
33 #define LUAI_HASHLIMIT 5
34 #endif
35
36
37 /*
38 ** equality for long strings
39 */
luaS_eqlngstr(TString * a,TString * b)40 int luaS_eqlngstr (TString *a, TString *b) {
41 size_t len = a->u.lnglen;
42 lua_assert(a->tt == LUA_TLNGSTR && b->tt == LUA_TLNGSTR);
43 return (a == b) || /* same instance or... */
44 ((len == b->u.lnglen) && /* equal length and ... */
45 (memcmp(getstr(a), getstr(b), len) == 0)); /* equal contents */
46 }
47
48
luaS_hash(const char * str,size_t l,unsigned int seed)49 unsigned int luaS_hash (const char *str, size_t l, unsigned int seed) {
50 unsigned int h = seed ^ cast(unsigned int, l);
51 size_t step = (l >> LUAI_HASHLIMIT) + 1;
52 for (; l >= step; l -= step)
53 h ^= ((h<<5) + (h>>2) + cast_byte(str[l - 1]));
54 return h;
55 }
56
luaS_hashlongstr(TString * ts)57 unsigned int luaS_hashlongstr (TString *ts) {
58 lua_assert(ts->tt == LUA_TLNGSTR);
59 if (ts->extra == 0) { /* no hash? */
60 ts->hash = luaS_hash(getstr(ts), ts->u.lnglen, ts->hash);
61 ts->extra = 1; /* now it has its hash */
62 }
63 return ts->hash;
64 }
65
66
67 /*
68 ** resizes the string table
69 */
luaS_resize(lua_State * L,int newsize)70 void luaS_resize (lua_State *L, int newsize) {
71 int i;
72 stringtable *tb = &G(L)->strt;
73 if (newsize > tb->size) { /* grow table if needed */
74 luaM_reallocvector(L, tb->hash, tb->size, newsize, TString *);
75 for (i = tb->size; i < newsize; i++)
76 tb->hash[i] = NULL;
77 }
78 for (i = 0; i < tb->size; i++) { /* rehash */
79 TString *p = tb->hash[i];
80 tb->hash[i] = NULL;
81 while (p) { /* for each node in the list */
82 TString *hnext = p->u.hnext; /* save next */
83 unsigned int h = lmod(p->hash, newsize); /* new position */
84 p->u.hnext = tb->hash[h]; /* chain it */
85 tb->hash[h] = p;
86 p = hnext;
87 }
88 }
89 if (newsize < tb->size) { /* shrink table if needed */
90 /* vanishing slice should be empty */
91 lua_assert(tb->hash[newsize] == NULL && tb->hash[tb->size - 1] == NULL);
92 luaM_reallocvector(L, tb->hash, tb->size, newsize, TString *);
93 }
94 tb->size = newsize;
95 }
96
97
98 /*
99 ** Clear API string cache. (Entries cannot be empty, so fill them with
100 ** a non-collectable string.)
101 */
luaS_clearcache(global_State * g)102 void luaS_clearcache (global_State *g) {
103 int i, j;
104 for (i = 0; i < STRCACHE_N; i++)
105 for (j = 0; j < STRCACHE_M; j++) {
106 if (iswhite(g->strcache[i][j])) /* will entry be collected? */
107 g->strcache[i][j] = g->memerrmsg; /* replace it with something fixed */
108 }
109 }
110
111
112 /*
113 ** Initialize the string table and the string cache
114 */
luaS_init(lua_State * L)115 void luaS_init (lua_State *L) {
116 global_State *g = G(L);
117 int i, j;
118 luaS_resize(L, MINSTRTABSIZE); /* initial size of string table */
119 /* pre-create memory-error message */
120 g->memerrmsg = luaS_newliteral(L, MEMERRMSG);
121 luaC_fix(L, obj2gco(g->memerrmsg)); /* it should never be collected */
122 for (i = 0; i < STRCACHE_N; i++) /* fill cache with valid strings */
123 for (j = 0; j < STRCACHE_M; j++)
124 g->strcache[i][j] = g->memerrmsg;
125 }
126
127
128
129 /*
130 ** creates a new string object
131 */
createstrobj(lua_State * L,size_t l,int tag,unsigned int h)132 static TString *createstrobj (lua_State *L, size_t l, int tag, unsigned int h) {
133 TString *ts;
134 GCObject *o;
135 size_t totalsize; /* total size of TString object */
136 char *str;
137 totalsize = sizelstring(l);
138 o = luaC_newobj(L, tag, totalsize);
139 ts = gco2ts(o);
140 ts->hash = h;
141 ts->extra = 0;
142 str = getstr(ts);
143 str[l] = '\0'; /* ending 0 */
144 return ts;
145 }
146
147
luaS_createlngstrobj(lua_State * L,size_t l)148 TString *luaS_createlngstrobj (lua_State *L, size_t l) {
149 TString *ts = createstrobj(L, l, LUA_TLNGSTR, G(L)->seed);
150 ts->u.lnglen = l;
151 return ts;
152 }
153
154
luaS_remove(lua_State * L,TString * ts)155 void luaS_remove (lua_State *L, TString *ts) {
156 stringtable *tb = &G(L)->strt;
157 TString **p = &tb->hash[lmod(ts->hash, tb->size)];
158 while (*p != ts) /* find previous element */
159 p = &(*p)->u.hnext;
160 *p = (*p)->u.hnext; /* remove element from its list */
161 tb->nuse--;
162 }
163
164
165 /*
166 ** checks whether short string exists and reuses it or creates a new one
167 */
internshrstr(lua_State * L,const char * str,size_t l)168 static TString *internshrstr (lua_State *L, const char *str, size_t l) {
169 TString *ts;
170 global_State *g = G(L);
171 unsigned int h = luaS_hash(str, l, g->seed);
172 TString **list = &g->strt.hash[lmod(h, g->strt.size)];
173 lua_assert(str != NULL); /* otherwise 'memcmp'/'memcpy' are undefined */
174 for (ts = *list; ts != NULL; ts = ts->u.hnext) {
175 if (l == ts->shrlen &&
176 (memcmp(str, getstr(ts), l * sizeof(char)) == 0)) {
177 /* found! */
178 if (isdead(g, ts)) /* dead (but not collected yet)? */
179 changewhite(ts); /* resurrect it */
180 return ts;
181 }
182 }
183 if (g->strt.nuse >= g->strt.size && g->strt.size <= MAX_INT/2) {
184 luaS_resize(L, g->strt.size * 2);
185 list = &g->strt.hash[lmod(h, g->strt.size)]; /* recompute with new size */
186 }
187 ts = createstrobj(L, l, LUA_TSHRSTR, h);
188 memcpy(getstr(ts), str, l * sizeof(char));
189 ts->shrlen = cast_byte(l);
190 ts->u.hnext = *list;
191 *list = ts;
192 g->strt.nuse++;
193 return ts;
194 }
195
196
197 /*
198 ** new string (with explicit length)
199 */
luaS_newlstr(lua_State * L,const char * str,size_t l)200 TString *luaS_newlstr (lua_State *L, const char *str, size_t l) {
201 if (l <= LUAI_MAXSHORTLEN) /* short string? */
202 return internshrstr(L, str, l);
203 else {
204 TString *ts;
205 if (l >= (MAX_SIZE - sizeof(TString))/sizeof(char))
206 luaM_toobig(L);
207 ts = luaS_createlngstrobj(L, l);
208 memcpy(getstr(ts), str, l * sizeof(char));
209 return ts;
210 }
211 }
212
213
214 /*
215 ** Create or reuse a zero-terminated string, first checking in the
216 ** cache (using the string address as a key). The cache can contain
217 ** only zero-terminated strings, so it is safe to use 'strcmp' to
218 ** check hits.
219 */
luaS_new(lua_State * L,const char * str)220 TString *luaS_new (lua_State *L, const char *str) {
221 unsigned int i = point2uint(str) % STRCACHE_N; /* hash */
222 int j;
223 TString **p = G(L)->strcache[i];
224 for (j = 0; j < STRCACHE_M; j++) {
225 if (strcmp(str, getstr(p[j])) == 0) /* hit? */
226 return p[j]; /* that is it */
227 }
228 /* normal route */
229 for (j = STRCACHE_M - 1; j > 0; j--)
230 p[j] = p[j - 1]; /* move out last element */
231 /* new element is first in the list */
232 p[0] = luaS_newlstr(L, str, strlen(str));
233 return p[0];
234 }
235
236
luaS_newudata(lua_State * L,size_t s)237 Udata *luaS_newudata (lua_State *L, size_t s) {
238 Udata *u;
239 GCObject *o;
240 if (s > MAX_SIZE - sizeof(Udata))
241 luaM_toobig(L);
242 o = luaC_newobj(L, LUA_TUSERDATA, sizeludata(s));
243 u = gco2u(o);
244 u->len = s;
245 u->metatable = NULL;
246 setuservalue(L, u, luaO_nilobject);
247 return u;
248 }
249
250