Function str_unpack

3rd/lua-5.4.3/src/lstrlib.c:1697–1768

static int str_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 = posrelatI(luaL_optinteger(L, 3, 1), ld) - 1;
  int n = 0;  /* number of results */
  luaL_argcheck(L, pos <= ld, 3, "initial position out of string");
  initheader(L, &h);
  while (*fmt != '\0') {
    int size, ntoalign;
    KOption opt = getdetails(&h, pos, &fmt, &size, &ntoalign);
    luaL_argcheck(L, (size_t)ntoalign + size <= ld - pos, 2,
                    "data string too short");
    pos += ntoalign;  /* skip alignment */
    /* stack space for item + next position */
    luaL_checkstack(L, 2, "too many results");
    n++;
    switch (opt) {
      case Kint:
      case Kuint: {
        lua_Integer res = unpackint(L, data + pos, h.islittle, size,
                                       (opt == Kint));
        lua_pushinteger(L, res);
        break;
      }
      case Kfloat: {
        float f;
        copywithendian((char *)&f, data + pos, sizeof(f), h.islittle);
        lua_pushnumber(L, (lua_Number)f);
        break;
      }
      case Knumber: {
        lua_Number f;
        copywithendian((char *)&f, data + pos, sizeof(f), h.islittle);
        lua_pushnumber(L, f);
        break;
      }
      case Kdouble: {
        double f;
        copywithendian((char *)&f, data + pos, sizeof(f), h.islittle);
        lua_pushnumber(L, (lua_Number)f);
        break;
      }
      case Kchar: {
        lua_pushlstring(L, data + pos, size);
        break;
      }
      case Kstring: {
        size_t len = (size_t)unpackint(L, data + pos, h.islittle, size, 0);
        luaL_argcheck(L, len <= ld - pos - size, 2, "data string too short");
        lua_pushlstring(L, data + pos + size, len);
        pos += len;  /* skip string */
        break;
      }
      case Kzstr: {
        size_t len = strlen(data + pos);
        luaL_argcheck(L, pos + len < ld, 2,