Function lua_arith

xrepo/packages/l/lua/port/lua/src/lapi.c:339–352

LUA_API void lua_arith (lua_State *L, int op) {
  lua_lock(L);
  if (op != LUA_OPUNM && op != LUA_OPBNOT)
    api_checknelems(L, 2);  /* all other operations expect two operands */
  else {  /* for unary operations, add fake 2nd operand */
    api_checknelems(L, 1);
    setobjs2s(L, L->top, L->top - 1);
    api_incr_top(L);
  }
  /* first operand at top - 2, second at top - 1; result go to top - 2 */
  luaO_arith(L, op, s2v(L->top - 2), s2v(L->top - 1), L->top - 2);
  L->top--;  /* remove second operand */
  lua_unlock(L);
}


LUA_API int lua_compare (lua_State *L, int index1, int index2, int op) {