Function lua_rotate

3rd/lua-5.4.3/src/lapi.c:235–246

** Let x = AB, where A is a prefix of length 'n'. Then, ** rotate x n == BA. But BA == (A^r . B^r)^r. */

** rotate x n == BA. But BA == (A^r . B^r)^r.
*/
LUA_API void lua_rotate (lua_State *L, int idx, int n) {
  StkId p, t, m;
  lua_lock(L);
  t = L->top - 1;  /* end of stack segment being rotated */
  p = index2stack(L, idx);  /* start of segment */
  api_check(L, (n >= 0 ? n : -n) <= (t - p + 1), "invalid 'n'");
  m = (n >= 0 ? t - n : p - n - 1);  /* end of prefix */
  reverse(L, p, m);  /* reverse the prefix with length 'n' */
  reverse(L, m + 1, t);  /* reverse the suffix */
  reverse(L, p, t);  /* reverse the entire segment */
  lua_unlock(L);
}


LUA_API void lua_copy (lua_State *L, int fromidx, int toidx) {