liblua/lstring.c

   1 /*
   2 ** $Id: lstring.c,v 2.26 2013/01/08 13:50:10 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