Re: Memory Size of 1 Mio Point Polyline table?

[Viacheslav Usov <via.usov@...>]

On Tue, Oct 25, 2022 at 7:47 AM bil til <biltil52@gmail.com> wrote:

> So if you set LUA_32BITS in case of a 32bit compiler

The key word here is "if".

>     #define TValuefields Value value_; unsigned char tt_
>
>   typedef union Value {
>     struct GCObject *gc;    /* collectable objects */
>     void *p;         /* light userdata */
>     lua_CFunction f; /* light C functions */
>     int i;   /* integer numbers */
>     float n;    /* float numbers */
>   } Value;

As already discussed, compilers would by default make structures at
least a multiple of 4 bytes on 32-bit platforms, thus struct {int foo;
char bar; } would be "wasting" at least three bytes. This is the
reason why Lua makes TValuefields a define rather than a struct,
because it is then fused with the other fields in derived structures,
thus recovering the wasted bytes.

This makes TValue 12 bytes on 32-bit platforms by default, which you
can check directly with printf("%d", sizeof TValue).

Cheers,
V.