Function luaD_shrinkstack

lib/lua/src/ldo.c:300–312

** If stack size is more than 3 times the current use, reduce that size ** to twice the current use. (So, the final stack size is at most 2/3 the ** previous size, and half of its entries are empty.) ** As a particular case, if stack was handling a stack overflow and now ** it is not, 'max' (limited by LUAI_MAXSTACK) will be smaller than ** stacksize (equal to ERRORSTACKSIZE in this case), and so

** will be reduced to a "regular" size.
*/
void luaD_shrinkstack (lua_State *L) {
  int inuse = stackinuse(L);
  int max = (inuse > LUAI_MAXSTACK / 3) ? LUAI_MAXSTACK : inuse * 3;
  /* if thread is currently not handling a stack overflow and its
     size is larger than maximum "reasonable" size, shrink it */
  if (inuse <= LUAI_MAXSTACK && stacksize(L) > max) {
    int nsize = (inuse > LUAI_MAXSTACK / 2) ? LUAI_MAXSTACK : inuse * 2;
    luaD_reallocstack(L, nsize, 0);  /* ok if that fails */
  }
  else  /* don't change stack */
    condmovestack(L,{},{});  /* (change only for debugging) */
  luaE_shrinkCI(L);  /* shrink CI list */
}


void luaD_inctop (lua_State *L) {