module/lua/lstring.c

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