Re: [boost] Interest request for pointer+bit compression optimization

Subject: Re: [boost] Interest request for pointer+bit compression optimization
From: Cory Nelson (phrosty_at_[hidden])
Date: 2009-09-08 20:36:54

On Tue, Sep 8, 2009 at 12:47 AM, Neil Groves <neil_at_[hidden]> wrote:
> On Mon, Sep 7, 2009 at 10:19 PM, Edouard A. <edouard_at_[hidden]> wrote:
>
>> >You appear to be assuming that the OS guarantees that it uses the lowest
>> >available virtual addresses. Would you please provide a link to the
>> >documentation? I was under the impression that the 8TB limit is merely a
>> >practical one since this was the maximum hardware specification available
>> >for testing.
>>
>> The OS isn't floating around in virtual memory space! The layout is strict
>> and doesn't change and of it's precisely and correctly documented in the
>> driver developer's manual.
>>
>>
> I would be alarmed if it was floating around. My concern was the perceived
> lack of documented guarantees. I was ignorant of any documentation with
> respect to the pointer ranges in the 64-bit Windows Operating Systems. My
> motivation was to clarify the safe useable ranges and ensure we weren't
> going to use undocumented implementation details by default.
>

The lock-free stack implementation in XP and Vista uses the high 21
bits of a 64-bit pointer for the ABA tag.  Undocumented implementation
detail, but at least it's not a complete mystery as to what should be
safe for use :)

-- 
Cory Nelson
http://int64.org