[linux-audio-dev] XAP spec - early scribbles

[Simon Jenkins]

Dave Griffiths wrote:

>>>I could have a quick go at fixing it up in the harness, give you 
>>>something you
>>>can drop in and try. Maybe code it so you can flip an alternative
>>>algorithm in and out.
>>>
Done it:

http://www.sbibble.pwp.blueyonder.co.uk/GraphSort.C
http://www.sbibble.pwp.blueyonder.co.uk/GraphSort.h

Nothing changes until/unless you either
a) compile with GRAPHSORT_USE_TEST_SORT_BY_DEFAULT defined
b) pass 'true' into the constructor OR
c) call GraphSort::TestSort() instead of GraphSort::Sort()

In any of which cases it uses the new TestSort() instead of the original
Sort(). This tries to replicate the original sort's quirks, whilst 
eliminating
the actual sort error.

>>>Would need to know...
>>>1) the exact semantics of "Terminal"... which nodes are marked
>>>terminal and why. I can see how/where they're marked, but haven't
>>>looked into why. (Maybe I should just read the code).
>>>      
>>>
>>Terminals are outputs... 
>>
>>there are input terminals but they are not used in 0.2.0...
>>    
>>
>
>Output terminal modules (OSS,Jack,DiskWriter)
>
Hadn't run ssm (I have now) so didn't know if outputs on a terminal
were feedback from the graph outputs or if they were inputs, ie it was
an I/O module.

> are needed to be flagged
>to resolve perfectly circular patches (eg Jack -> Echo -> Jack). The
>Graphsort falls back on this if it can't find a root by itself.
>
... and didn't understand this as being "circular"... I see it as a 
straight line
that comes in, through and out of the app, so I thought "terminals" must
be somewhere on a free-floating circle of modules. I see now what you
mean by circular.

>>>2) any non-obvious requirements on the sort order.
>>>3) how, if at all, the rest of the app is sensitive to the internal 
>>>implementation
>>>of the GraphSort class.
>>>      
>>>
>>Sort is only called from GraphSort.C seems to be ok for you....
>>    
>>
>
>Indeed, the implementation shouldn't affect anything else. No special
>requirements that I can think of, except it shouldn't be too slow, but
>it's currently a recursive function it probably couldn't get much slower
>- and it doesn't impact the performance at the moment.
>
OK. TestSort() manages to avoid recursion by using an intermediate list.

Note: I've tried to give this a half decent test, and it does seem to 
work every
time, but your original code has executed successfully about a zillion times
more than this code has...

Simon Jenkins
(Bristol, UK)