---- Le ven., 26 févr. 2021 23:13:56 -0500 Jessica Clarke <jrt...@debian.org>
écrit ----
>
> The low 3 bits of the actual size are known to always be 0, so they
> aren't stored and instead replaced with the 3 flags. The diagram
> doesn't make that overly clear, but if you re-read all the text it
> should. Pictorially (not to scale):
>
> +-------------------------+
> | Size in bytes |
> | High bits of size |A|M|P|
> +-------------------+-+-+-+
>
> Alternatively, you can imagine that the value stored is indeed missing
> 3 bits, but it's also stored with 3 extra bits shoved on the end; you
> could then recover the original value by ((x >> 3) << 3), but that's
> the same as (x & ~7).
>
> Jess
>
>
Oh, you means the size is always a multiple of 8.
It make sense with:
Alignment: 2 * sizeof(size_t) (default)
(i.e., 8 byte alignment with 4byte size_t). This suffices for
nearly all current machines and C compilers. However, you can
define MALLOC_ALIGNMENT to be wider than this if necessary.
I see... I kind of sad I did not make a great discovery.
