Home | History | Annotate | Download | only in src
      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 
    186