Re: Lua 5.3w2 Test Suite Issues

[Doug Currie <doug.currie@...>]

On Sun, Mar 30, 2014 at 9:46 PM, Paige DePol <lual@serfnet.org> wrote:

Another way of fixing the issue ...

Reminder: this issue is present in 5.2 as well.

A portable solution for fixing unpack (without changing lua_checkstack) using unsigned arithmetic:

static int unpack (lua_State *L) {

  int i, e;

  unsigned int n;

  luaL_checktype(L, 1, LUA_TTABLE);

  i = luaL_optint(L, 2, 1);

  e = luaL_opt(L, luaL_checkint, 3, luaL_len(L, 1));

  if (i > e) return 0;  /* empty range */

  n = (unsigned int )e - (unsigned int )i;  /* number of elements minus one */

  if (n >= INT_MAX || !lua_checkstack(L, (int )(n+1)))  /* detect arith. overflow */

    return luaL_error(L, "too many results to unpack");

  lua_rawgeti(L, 1, i);  /* push arg[i] (avoiding overflow problems) */

  while (i++ < e)  /* push arg[i + 1...e] */

    lua_rawgeti(L, 1, i);

  return n;

}

The variable n is changed to unsigned, and the calculation of the number of elements uses unsigned arithmetic. This works because unsigned arithmetic cannot overflow; we know the sign of the result is positive since i <= e. Note that we defer the addition of 1 to n until after the test against INT_MAX to avoid a carry in the case of unpack ({}, -2^31, 2^31-1) leading to a result of zero.

e