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```On Monday, 11 June 2012 at 18:23:39 UTC, Roman D. Boiko wrote:
> On Monday, 11 June 2012 at 18:16:45 UTC, Dmitry Olshansky wrote:
>> I meant an operation pseudo-XOR x P^ y where x is part of snapshot and y is part of diff page.
>>
>> x P^ y == x      when y == T.init
>> x P^ y == y      when y != T.init
> I understood, just mentioned some alternatives (maybe not reasonable given your trie implementation).
Or probably not understood :)

Why pseudo?
```
```On Monday, 11 June 2012 at 18:27:58 UTC, Roman D. Boiko wrote:
> On Monday, 11 June 2012 at 18:23:39 UTC, Roman D. Boiko wrote:
>> On Monday, 11 June 2012 at 18:16:45 UTC, Dmitry Olshansky wrote:
>>> I meant an operation pseudo-XOR x P^ y where x is part of snapshot and y is part of diff page.
>>>
>>> x P^ y == x      when y == T.init
>>> x P^ y == y      when y != T.init
>> I understood, just mentioned some alternatives (maybe not reasonable given your trie implementation).
> Or probably not understood :)
>
> Why pseudo?
http://iwct.sjtu.edu.cn/Personal/mxtao/paper/liujc_icc11_PID1075548.pdf

I couldn't google anything more useful so far.
```
```On 11.06.2012 22:30, Roman D. Boiko wrote:
> On Monday, 11 June 2012 at 18:27:58 UTC, Roman D. Boiko wrote:
>> On Monday, 11 June 2012 at 18:23:39 UTC, Roman D. Boiko wrote:
>>> On Monday, 11 June 2012 at 18:16:45 UTC, Dmitry Olshansky wrote:
>>>> I meant an operation pseudo-XOR x P^ y where x is part of snapshot
>>>> and y is part of diff page.
>>>>
>>>> x P^ y == x when y == T.init
>>>> x P^ y == y when y != T.init
>>> I understood, just mentioned some alternatives (maybe not reasonable
>> Or probably not understood :)
>>
>> Why pseudo?
0 ^ 0 = 1 while T.init P^ T.init == T.init :)
other are almot the same
but
1 ^ 1 = 0 while x P^ y == y
So it's not symmetric when x,y != T.init for starters ;)

> Is this article somehow related, or just uses the same term?
> http://iwct.sjtu.edu.cn/Personal/mxtao/paper/liujc_icc11_PID1075548.pdf
>
looks like it might be but I can't penetrate this scientish somehow ( I usually can) in any case I believe it's more of coincidence.

--
Dmitry Olshansky
```
```On Monday, 11 June 2012 at 18:42:14 UTC, Dmitry Olshansky wrote:
> 0 ^ 0 = 1 while T.init P^ T.init == T.init :)
> other are almot the same but
> 1 ^ 1 = 0 while x P^ y == y
> So it's not symmetric when x,y != T.init for starters ;)

Just a remark that DCT no longer needs tries to be immutable, since I decided not to backtrack which strings affect which syntax elements. OTOH, it is important to be able to do updates and reads at any time (intermixed).

Another note is that XOR makes sense only if you plan to do reverse transforms, or expect to pack diffs (if they will be sparse). Otherwise it would be more efficient to store new values directly.
```
```On 24-Jun-12 14:50, Roman D. Boiko wrote:
> On Monday, 11 June 2012 at 18:42:14 UTC, Dmitry Olshansky wrote:
>> 0 ^ 0 = 1 while T.init P^ T.init == T.init :)
>> other are almot the same but
>> 1 ^ 1 = 0 while x P^ y == y
>> So it's not symmetric when x,y != T.init for starters ;)
>
> Just a remark that DCT no longer needs tries to be immutable, since I
> decided not to backtrack which strings affect which syntax elements.
> OTOH, it is important to be able to do updates and reads at any time
> (intermixed).
>
> Another note is that XOR makes sense only if you plan to do reverse
> transforms, or expect to pack diffs (if they will be sparse). Otherwise
> it would be more efficient to store new values directly.

Storing new values directly is no easy trick as you need crawl page tables all the way up to see if this value corresponds to multiple indexes. Well something similar happens with diff trie anyway.

But diffs are indeed very sparse, and the trie itself usually also sparse.
--
Dmitry Olshansky

```
```Am Mon, 04 Jun 2012 23:18:31 +0400
schrieb Dmitry Olshansky <dmitry.olsh@gmail.com>:

> Compiler is like a nasty stepchild it will give up on generating good old jump tables given any reason it finds justifiable. (but it may use few small jump tables + binary search, could be fine... if not in a tight loop!)

Looks, like you are back in control.

From http://gcc.gnu.org/gcc-4.7/changes.html :

** General Optimizer Improvements **

Support for a new parameter --param case-values-threshold=n was added to allow users to control the cutoff between doing switch statements as a series of if statements and using a jump table.

--
Marco

```
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