short pointers (32 bit) in 64 bit apps

[Reza Roboubi]

Nicholas Sherlock wrote:
> On 19/05/2010 8:54 p.m., Reza Roboubi wrote:
>> Nicholas Sherlock wrote:
>>> On 19/05/2010 3:58 p.m., Reza Roboubi wrote:
>>>> Do you know what it takes to do it? How much work for a newcomer to get
>>>> up to speed with gcc? (Maybe this should go to the developer list?)
>>>
>>> You would need to write a memory allocator which divides the address
>>> space into 4GB (32-bit pages). Then you could create a new malloc
>>> routine which has an extra argument to allow you to allocate memory
>>> from within a specified 4GB page. That way you can make all of your
>>> allocations for a given data structure lie within the same region.
>>
>> Since we are trying to _compress_ these structs in the first place
>> malloc'ing them individually is pointless anyway. We should probably
>> have some sort of custom (fixed size) allocator.
> 
> If the pointers only have to refer to memory within the same memory 
> allocation, and that allocation is smaller than 4GB, that's a 
> significantly more restricted problem. You wouldn't need a custom memory 
> allocator, you could just store the difference between the pointer 
> target and the pointer's location instead of an absolute pointer. That 
> sounds doable.

And that gets your ALU's doing a lot of unneeded additions and 
subtractions, every time you access such pointers.

Reza.