By storing the used flag in the LSB, it is no longer necessary to have
a size_mask variable to locate that flag. This produces smaller and
faster code.
Replace the validation check in chunk_set() to base it on the storage
type.
Also clarify the semantics of set_chunk_size() which allows for clearing
the used flag bit unconditionally which simplifies the code further.
The idea of moving the used flag bit into the LEFT_SIZE field was
raised. It turns out that this isn't as beneficial as it may seem
because the used bit is set only once i.e. when the memory is handed off
to a user and the size field becomes frozen at that point. Modifications
on the leftward chunk may still occur and extra instructions to preserve
that bit would be necessary if it were moved there.
Signed-off-by: Nicolas Pitre <npitre@baylibre.com>
e2b64777e5