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