Hi Akim,
> That doesn't ring any bell. I don't remember I saw any feature in bitset
> that depends on consecutive set bits, and a quick search did not find
> anything.
OK.
> Conversely: couldn't ssfmalloc sit on top of bitset?
Well, in ssfmalloc it is important to use the available space well. When
I use a bitset of 256 bits in order to describe which of the 16-byte blocks
of a 4096-bytes page are free, this requires 8 32-bit words. Now adding
5 (32-bit or 64-bit) words as meta-information, as defined per these
type definitions:
typedef union bitset_union *bitset;
union bitset_union
{
...
struct abitset_struct
{
struct bbitset_struct b;
bitset_word words[1]; /* The array of bits. */
} a;
...
};
struct bbitset_struct
{
const struct bitset_vtable *vtable;
bitset_windex cindex; /* Cache word index. */
bitset_windex csize; /* Cache size in words. */
bitset_word *cdata; /* Cache data pointer. */
bitset_bindex n_bits; /* Number of bits. */
/* Perhaps we could sacrifice another word to indicate
that the bitset is known to be zero, that a bit has been set
in the cache, and that a bit has been cleared in the cache.
This would speed up some of the searches but slightly slow down
bit set/reset operations of cached bits. */
};
is not really desirable. It would be only 1% waste, but the percents add up.
In other words, the 'bitset' module - while generally good for applications -
is one level too complex for this particular use-case.
Bruno
