lstring.c revision 344220 
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*/
40int 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
49unsigned 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
58unsigned 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*/
71void 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*/
103void 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*/
116void 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*/
133static 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
147TString *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
154void 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*/
167static 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*/
199TString *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*/
219TString *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
236Udata *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