static int b_unpack (lua_State *L) {
  Header h;
   const char *fmt = luaL_checkstring(L, 1);
   size_t ld;
   const char *data = luaL_checklstring(L, 2, &ld);
  size_t pos = luaL_optinteger(L, 3, 1);
  luaL_argcheck(L, pos > 0, 3, "offset must be 1 or greater");
  pos--; /* Lua indexes are 1-based, but here we want 0-based for C
          * pointer math. */
   int n = 0;  /* number of results */
   defaultoptions(&h);
   while (*fmt) {
     int opt = *fmt++;
     size_t size = optsize(L, opt, &fmt);
     pos += gettoalign(pos, &h, opt, size);
    luaL_argcheck(L, size <= ld && pos <= ld - size,
                   2, "data string too short");
     /* stack space for item + next position */
     luaL_checkstack(L, 2, "too many results");
     switch (opt) {
      case 'b': case 'B': case 'h': case 'H':
      case 'l': case 'L': case 'T': case 'i':  case 'I': {  /* integer types */
        int issigned = islower(opt);
        lua_Number res = getinteger(data+pos, h.endian, issigned, size);
        lua_pushnumber(L, res); n++;
        break;
      }
      case 'x': {
        break;
      }
      case 'f': {
        float f;
        memcpy(&f, data+pos, size);
        correctbytes((char *)&f, sizeof(f), h.endian);
        lua_pushnumber(L, f); n++;
        break;
      }
      case 'd': {
        double d;
        memcpy(&d, data+pos, size);
        correctbytes((char *)&d, sizeof(d), h.endian);
        lua_pushnumber(L, d); n++;
        break;
      }
      case 'c': {
        if (size == 0) {
          if (n == 0 || !lua_isnumber(L, -1))
            luaL_error(L, "format 'c0' needs a previous size");
          size = lua_tonumber(L, -1);
          lua_pop(L, 1); n--;
          luaL_argcheck(L, size <= ld && pos <= ld - size,
                           2, "data string too short");
        }
        lua_pushlstring(L, data+pos, size); n++;
        break;
      }
      case 's': {
        const char *e = (const char *)memchr(data+pos, '\0', ld - pos);
        if (e == NULL)
          luaL_error(L, "unfinished string in data");
        size = (e - (data+pos)) + 1;
        lua_pushlstring(L, data+pos, size - 1); n++;
        break;
      }
      default: controloptions(L, opt, &fmt, &h);
    }
    pos += size;
  }
  lua_pushinteger(L, pos + 1);  /* next position */
  return n + 1;
}

The product performs a calculation that can produce an integer overflow or wraparound when the logic assumes that the resulting value will always be larger than the original value. This occurs when an integer value is incremented to a value that is too large to store in the associated representation. When this occurs, the value may become a very small or negative number.