On 11 April 2007 12:53, Andi Kleen wrote:
> Richard Henderson <[EMAIL PROTECTED]> writes:
>
>> On Tue, Apr 10, 2007 at 11:13:44AM -0700, Ian Lance Taylor wrote:
>>> The obvious way to make the proposed tuples position independent would
>>> be to use array offsets rather than pointers.
>>
>> I suggest instead, if we want something like this, that we make
>> the references be pc-relative. So something like
>
> If you go this way (and require special GC/debugger support) you
> could as well xor next/prev too and save another field.
>
> Adding a xor is basically free and much cheaper than any cache miss
> from larger data structures.
Using a delta is even better than an XOR, because it remains constant when
you relocate the data.
> The only thing that wouldn't work is that when you have a pointer
> to an arbitary element (without starting from beginning/end first)
> you couldn't get previous or next.
You need a pointer to two consecutive nodes to act as an iterator.
However we already discussed the whole idea upthread and the general feeling
was that it's a whole bunch of tricky code for a small saving, so not worth
doing in the first iteration. Maybe as a future refinement. See the earlier
posts in this thread for the discussion.
cheers,
DaveK
--
Can't think of a witty .sigline today....
