size of short strings stored in a single byte, to reduce the size

of struct 'TString'

lstring.c

@@ -1,5 +1,5 @@
 /*
-** $Id: lstring.c,v 2.44 2014/07/21 16:02:10 roberto Exp roberto $
+** $Id: lstring.c,v 2.45 2014/11/02 19:19:04 roberto Exp roberto $
 ** String table (keeps all strings handled by Lua)
 ** See Copyright Notice in lua.h
 */
@@ -36,10 +36,10 @@
 ** equality for long strings
 */
 int luaS_eqlngstr (TString *a, TString *b) {
-  size_t len = a->len;
+  size_t len = a->u.lnglen;
   lua_assert(a->tt == LUA_TLNGSTR && b->tt == LUA_TLNGSTR);
   return (a == b) ||  /* same instance or... */
-    ((len == b->len) &&  /* equal length and ... */
+    ((len == b->u.lnglen) &&  /* equal length and ... */
      (memcmp(getstr(a), getstr(b), len) == 0));  /* equal contents */
 }
 
@@ -69,9 +69,9 @@ void luaS_resize (lua_State *L, int newsize) {
     TString *p = tb->hash[i];
     tb->hash[i] = NULL;
     while (p) {  /* for each node in the list */
-      TString *hnext = p->hnext;  /* save next */
+      TString *hnext = p->u.hnext;  /* save next */
       unsigned int h = lmod(p->hash, newsize);  /* new position */
-      p->hnext = tb->hash[h];  /* chain it */
+      p->u.hnext = tb->hash[h];  /* chain it */
       tb->hash[h] = p;
       p = hnext;
     }
@@ -97,7 +97,6 @@ static TString *createstrobj (lua_State *L, const char *str, size_t l,
   totalsize = sizelstring(l);
   o = luaC_newobj(L, tag, totalsize);
   ts = gco2ts(o);
-  ts->len = l;
   ts->hash = h;
   ts->extra = 0;
   memcpy(getaddrstr(ts), str, l * sizeof(char));
@@ -110,8 +109,8 @@ void luaS_remove (lua_State *L, TString *ts) {
   stringtable *tb = &G(L)->strt;
   TString **p = &tb->hash[lmod(ts->hash, tb->size)];
   while (*p != ts)  /* find previous element */
-    p = &(*p)->hnext;
-  *p = (*p)->hnext;  /* remove element from its list */
+    p = &(*p)->u.hnext;
+  *p = (*p)->u.hnext;  /* remove element from its list */
   tb->nuse--;
 }
 
@@ -124,8 +123,8 @@ static TString *internshrstr (lua_State *L, const char *str, size_t l) {
   global_State *g = G(L);
   unsigned int h = luaS_hash(str, l, g->seed);
   TString **list = &g->strt.hash[lmod(h, g->strt.size)];
-  for (ts = *list; ts != NULL; ts = ts->hnext) {
-    if (l == ts->len &&
+  for (ts = *list; ts != NULL; ts = ts->u.hnext) {
+    if (l == ts->shrlen &&
         (memcmp(str, getstr(ts), l * sizeof(char)) == 0)) {
       /* found! */
       if (isdead(g, ts))  /* dead (but not collected yet)? */
@@ -138,7 +137,8 @@ static TString *internshrstr (lua_State *L, const char *str, size_t l) {
     list = &g->strt.hash[lmod(h, g->strt.size)];  /* recompute with new size */
   }
   ts = createstrobj(L, str, l, LUA_TSHRSTR, h);
-  ts->hnext = *list;
+  ts->shrlen = cast_byte(l);
+  ts->u.hnext = *list;
   *list = ts;
   g->strt.nuse++;
   return ts;
@@ -152,9 +152,12 @@ TString *luaS_newlstr (lua_State *L, const char *str, size_t l) {
   if (l <= LUAI_MAXSHORTLEN)  /* short string? */
     return internshrstr(L, str, l);
   else {
+    TString *ts;
     if (l + 1 > (MAX_SIZE - sizeof(TString))/sizeof(char))
       luaM_toobig(L);
-    return createstrobj(L, str, l, LUA_TLNGSTR, G(L)->seed);
+    ts = createstrobj(L, str, l, LUA_TLNGSTR, G(L)->seed);
+    ts->u.lnglen = l;
+    return ts;
   }
 }