lua 5.2.3 source lstring.c function luaS_resize

Question

void luaS_resize (lua_State *L, int newsize) {
  int i;
  stringtable *tb = &G(L)->strt;
  /* cannot resize while GC is traversing strings */
  luaC_runtilstate(L, ~bitmask(GCSsweepstring));
  if (newsize > tb->size) {
    luaM_reallocvector(L, tb->hash, tb->size, newsize, GCObject *);
    for (i = tb->size; i < newsize; i++) tb->hash[i] = NULL;
  }
  /* rehash */
  for (i=0; i<tb->size; i++) {
    GCObject *p = tb->hash[i];
    tb->hash[i] = NULL;
    while (p) {  /* for each node in the list */
      GCObject *next = gch(p)->next;  /* save next */
      unsigned int h = lmod(gco2ts(p)->hash, newsize);  /* new position */
      gch(p)->next = tb->hash[h];  /* chain it */
      tb->hash[h] = p;
      resetoldbit(p);  /* see MOVE OLD rule */
      p = next;
    }
  }
  if (newsize < tb->size) {
    /* shrinking slice must be empty */
    lua_assert(tb->hash[newsize] == NULL && tb->hash[tb->size - 1] == NULL);
    luaM_reallocvector(L, tb->hash, tb->size, newsize, GCObject *);
  }
  tb->size = newsize;
}

When the table grows, it rehashes. But when the table shrinks, it just realloc with a half size without rehash. I can't understand it. How can it work ?

Answer 1

Well. I answer this question myself. This code works well because the rehash operation is not in the first if(newsize > tb->size). It works for both (newsize > tb->size) and (newsize < tb->size). Next time, I will read code more carefully.