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  1. /*
  2. ** $Id: lstring.c,v 2.26.1.1 2013/04/12 18:48:47 roberto Exp $
  3. ** String table (keeps all strings handled by Lua)
  4. ** See Copyright Notice in lua.h
  5. */
  6.  
  7.  
  8. #include <string.h>
  9.  
  10. #define lstring_c
  11. #define LUA_CORE
  12.  
  13. #include "lua.h"
  14.  
  15. #include "lmem.h"
  16. #include "lobject.h"
  17. #include "lstate.h"
  18. #include "lstring.h"
  19.  
  20.  
  21. /*
  22. ** Lua will use at most ~(2^LUAI_HASHLIMIT) bytes from a string to
  23. ** compute its hash
  24. */
  25. #if !defined(LUAI_HASHLIMIT)
  26. #define LUAI_HASHLIMIT          5
  27. #endif
  28.  
  29.  
  30. /*
  31. ** equality for long strings
  32. */
  33. int luaS_eqlngstr (TString *a, TString *b) {
  34.   size_t len = a->tsv.len;
  35.   lua_assert(a->tsv.tt == LUA_TLNGSTR && b->tsv.tt == LUA_TLNGSTR);
  36.   return (a == b) ||  /* same instance or... */
  37.     ((len == b->tsv.len) &&  /* equal length and ... */
  38.      (memcmp(getstr(a), getstr(b), len) == 0));  /* equal contents */
  39. }
  40.  
  41.  
  42. /*
  43. ** equality for strings
  44. */
  45. int luaS_eqstr (TString *a, TString *b) {
  46.   return (a->tsv.tt == b->tsv.tt) &&
  47.          (a->tsv.tt == LUA_TSHRSTR ? eqshrstr(a, b) : luaS_eqlngstr(a, b));
  48. }
  49.  
  50.  
  51. unsigned int luaS_hash (const char *str, size_t l, unsigned int seed) {
  52.   unsigned int h = seed ^ cast(unsigned int, l);
  53.   size_t l1;
  54.   size_t step = (l >> LUAI_HASHLIMIT) + 1;
  55.   for (l1 = l; l1 >= step; l1 -= step)
  56.     h = h ^ ((h<<5) + (h>>2) + cast_byte(str[l1 - 1]));
  57.   return h;
  58. }
  59.  
  60.  
  61. /*
  62. ** resizes the string table
  63. */
  64. void luaS_resize (lua_State *L, int newsize) {
  65.   int i;
  66.   stringtable *tb = &G(L)->strt;
  67.   /* cannot resize while GC is traversing strings */
  68.   luaC_runtilstate(L, ~bitmask(GCSsweepstring));
  69.   if (newsize > tb->size) {
  70.     luaM_reallocvector(L, tb->hash, tb->size, newsize, GCObject *);
  71.     for (i = tb->size; i < newsize; i++) tb->hash[i] = NULL;
  72.   }
  73.   /* rehash */
  74.   for (i=0; i<tb->size; i++) {
  75.     GCObject *p = tb->hash[i];
  76.     tb->hash[i] = NULL;
  77.     while (p) {  /* for each node in the list */
  78.       GCObject *next = gch(p)->next;  /* save next */
  79.       unsigned int h = lmod(gco2ts(p)->hash, newsize);  /* new position */
  80.       gch(p)->next = tb->hash[h];  /* chain it */
  81.       tb->hash[h] = p;
  82.       resetoldbit(p);  /* see MOVE OLD rule */
  83.       p = next;
  84.     }
  85.   }
  86.   if (newsize < tb->size) {
  87.     /* shrinking slice must be empty */
  88.     lua_assert(tb->hash[newsize] == NULL && tb->hash[tb->size - 1] == NULL);
  89.     luaM_reallocvector(L, tb->hash, tb->size, newsize, GCObject *);
  90.   }
  91.   tb->size = newsize;
  92. }
  93.  
  94.  
  95. /*
  96. ** creates a new string object
  97. */
  98. static TString *createstrobj (lua_State *L, const char *str, size_t l,
  99.                               int tag, unsigned int h, GCObject **list) {
  100.   TString *ts;
  101.   size_t totalsize;  /* total size of TString object */
  102.   totalsize = sizeof(TString) + ((l + 1) * sizeof(char));
  103.   ts = &luaC_newobj(L, tag, totalsize, list, 0)->ts;
  104.   ts->tsv.len = l;
  105.   ts->tsv.hash = h;
  106.   ts->tsv.extra = 0;
  107.   memcpy(ts+1, str, l*sizeof(char));
  108.   ((char *)(ts+1))[l] = '\0';  /* ending 0 */
  109.   return ts;
  110. }
  111.  
  112.  
  113. /*
  114. ** creates a new short string, inserting it into string table
  115. */
  116. static TString *newshrstr (lua_State *L, const char *str, size_t l,
  117.                                        unsigned int h) {
  118.   GCObject **list;  /* (pointer to) list where it will be inserted */
  119.   stringtable *tb = &G(L)->strt;
  120.   TString *s;
  121.   if (tb->nuse >= cast(lu_int32, tb->size) && tb->size <= MAX_INT/2)
  122.     luaS_resize(L, tb->size*2);  /* too crowded */
  123.   list = &tb->hash[lmod(h, tb->size)];
  124.   s = createstrobj(L, str, l, LUA_TSHRSTR, h, list);
  125.   tb->nuse++;
  126.   return s;
  127. }
  128.  
  129.  
  130. /*
  131. ** checks whether short string exists and reuses it or creates a new one
  132. */
  133. static TString *internshrstr (lua_State *L, const char *str, size_t l) {
  134.   GCObject *o;
  135.   global_State *g = G(L);
  136.   unsigned int h = luaS_hash(str, l, g->seed);
  137.   for (o = g->strt.hash[lmod(h, g->strt.size)];
  138.        o != NULL;
  139.        o = gch(o)->next) {
  140.     TString *ts = rawgco2ts(o);
  141.     if (h == ts->tsv.hash &&
  142.         l == ts->tsv.len &&
  143.         (memcmp(str, getstr(ts), l * sizeof(char)) == 0)) {
  144.       if (isdead(G(L), o))  /* string is dead (but was not collected yet)? */
  145.         changewhite(o);  /* resurrect it */
  146.       return ts;
  147.     }
  148.   }
  149.   return newshrstr(L, str, l, h);  /* not found; create a new string */
  150. }
  151.  
  152.  
  153. /*
  154. ** new string (with explicit length)
  155. */
  156. TString *luaS_newlstr (lua_State *L, const char *str, size_t l) {
  157.   if (l <= LUAI_MAXSHORTLEN)  /* short string? */
  158.     return internshrstr(L, str, l);
  159.   else {
  160.     if (l + 1 > (MAX_SIZET - sizeof(TString))/sizeof(char))
  161.       luaM_toobig(L);
  162.     return createstrobj(L, str, l, LUA_TLNGSTR, G(L)->seed, NULL);
  163.   }
  164. }
  165.  
  166.  
  167. /*
  168. ** new zero-terminated string
  169. */
  170. TString *luaS_new (lua_State *L, const char *str) {
  171.   return luaS_newlstr(L, str, strlen(str));
  172. }
  173.  
  174.  
  175. Udata *luaS_newudata (lua_State *L, size_t s, Table *e) {
  176.   Udata *u;
  177.   if (s > MAX_SIZET - sizeof(Udata))
  178.     luaM_toobig(L);
  179.   u = &luaC_newobj(L, LUA_TUSERDATA, sizeof(Udata) + s, NULL, 0)->u;
  180.   u->uv.len = s;
  181.   u->uv.metatable = NULL;
  182.   u->uv.env = e;
  183.   return u;
  184. }
  185.  
  186.