Function str_pack

3rd/lua-5.4.3/src/lstrlib.c:1544–1640

static int str_pack (lua_State *L) {
  luaL_Buffer b;
  Header h;
  const char *fmt = luaL_checkstring(L, 1);  /* format string */
  int arg = 1;  /* current argument to pack */
  size_t totalsize = 0;  /* accumulate total size of result */
  initheader(L, &h);
  lua_pushnil(L);  /* mark to separate arguments from string buffer */
  luaL_buffinit(L, &b);
  while (*fmt != '\0') {
    int size, ntoalign;
    KOption opt = getdetails(&h, totalsize, &fmt, &size, &ntoalign);
    totalsize += ntoalign + size;
    while (ntoalign-- > 0)
     luaL_addchar(&b, LUAL_PACKPADBYTE);  /* fill alignment */
    arg++;
    switch (opt) {
      case Kint: {  /* signed integers */
        lua_Integer n = luaL_checkinteger(L, arg);
        if (size < SZINT) {  /* need overflow check? */
          lua_Integer lim = (lua_Integer)1 << ((size * NB) - 1);
          luaL_argcheck(L, -lim <= n && n < lim, arg, "integer overflow");
        }
        packint(&b, (lua_Unsigned)n, h.islittle, size, (n < 0));
        break;
      }
      case Kuint: {  /* unsigned integers */
        lua_Integer n = luaL_checkinteger(L, arg);
        if (size < SZINT)  /* need overflow check? */
          luaL_argcheck(L, (lua_Unsigned)n < ((lua_Unsigned)1 << (size * NB)),
                           arg, "unsigned overflow");
        packint(&b, (lua_Unsigned)n, h.islittle, size, 0);
        break;
      }
      case Kfloat: {  /* C float */
        float f = (float)luaL_checknumber(L, arg);  /* get argument */
        char *buff = luaL_prepbuffsize(&b, sizeof(f));
        /* move 'f' to final result, correcting endianness if needed */
        copywithendian(buff, (char *)&f, sizeof(f), h.islittle);
        luaL_addsize(&b, size);
        break;
      }
      case Knumber: {  /* Lua float */
        lua_Number f = luaL_checknumber(L, arg);  /* get argument */
        char *buff = luaL_prepbuffsize(&b, sizeof(f));
        /* move 'f' to final result, correcting endianness if needed */
        copywithendian(buff, (char *)&f, sizeof(f), h.islittle);
        luaL_addsize(&b, size);
        break;
      }
      case Kdouble: {  /* C double */
        double f = (double)luaL_checknumber(L, arg);  /* get argument */
        char *buff = luaL_prepbuffsize(&b, sizeof(f));
        /* move 'f' to final result, correcting endianness if needed */
        copywithendian(buff, (char *)&f, sizeof(f), h.islittle);
        luaL_addsize(&b, size);
        break;
      }