Author: Christophe Theron
Date: 15:31:11 01/05/01
Go up one level in this thread
On January 05, 2001 at 12:11:05, Ian Osgood wrote:
>On January 04, 2001 at 12:07:27, Christophe Theron wrote:
>
>>On January 04, 2001 at 08:04:07, Tord Romstad wrote:
>>
>>>On January 03, 2001 at 12:26:00, Christophe Theron wrote:
>>>
>>>>On January 03, 2001 at 07:48:12, Tord Romstad wrote:
>>>>
>>>>>I apologise for the misunderstanding, I was reading too fast. However, I
>>>>>still think you are a little bit too optimistic. Mephisto Berlin did use
>>>>>transposition tables. If I understand correctly, transposition tables are
>>>>>difficult or impossible to implement in PalmOS.
>>>>>
>>>>>
>>>>>Tord
>>>>
>>>>Hash tables slow the program down a little bit under PalmOS (about 5%), but
>>>>there is no problem to implement them.
>>>
>>>OK. I should probably stop talking about things I have no first-hand
>>>knowledge about. I thought I had read somewhere that a PalmOS program
>>>could only allocate a relatively small amount of memory.
>>>
>>>Tord
>>
>>
>>
>>
>>You can allocate as much as you want, but in small chunks (max 64Kb). For hash
>>table management, having to deal with a large hash table split into small chunks
>>is not really a problem.
>>
>>
>>
>> Christophe
>
>Interesting... is this heap allocation (SDRAM) or storage allocation (Flash)? I
>was under the impression that current Palm devices had only small amounts of RAM
>for the running program storage and heap (<= 1MB) and that the advertised 8MB
>storage of a Palm device was all Flash memory. Flash memory is unsuitable for
>transposition tables because 1) it is slow and power hungry to write to, 2) you
>have to write (and maybe read) large blocks of data at a time, and 3) Flash
>memory wears out after too much writing (maybe a million writes the the same
>address?).
The program that is running has only access to a few Kb of RAM for its
data+stack+heap. That's the problem of the Palm, this amount is too small for
many applications.
The rest of the memory is SDRAM, but it is controlled by the OS. You cannot
write directly into it, which is the reason why an app that crashes CANNOT
destroy other apps data. It can only destroy its own few Kb of data, but not
damage the rest.
But you can allocate and read large chunks of memory. However you will have to
access it thru OS calls, which makes them slower to access of course.
So a chess program using hash tables under PalmOS will be slowed down for this
reason. But depending on the philosophy of the program, it is maybe not a
serious problem.
A program with a "high" NPS will definitely be handicapped by this problem
(maybe it is the reason why ChessGenius for Palm does not have hash tables). If
you can compute a position every millisecond and every hash table access takes
one millisecond and you have to access the hash table for every position, then
your program is going to be twice as slow!
But if you can compute only one position every ten millisecond, then having to
wait one millisecond for a hash table access is only a 10% slowdown...
Christophe
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