[CELT-dev] Possible Bug

[Riccardo Micci]

Decoding the second frame the function unquant_fine_energy is executed. 
Within it ec_dec_bits subfunction is executed (q2 = ec_dec_bits(dec, 
fine_quant[i]);). Ec_dec_bits calls ec_decode_raw 
(s=ec_decode_raw(_this,_ftb);).
In ec_decode_raw within the while loop the following line is executed:
value |= _this->end_byte>>(8-_this->end_bits_left)<<count;
As you can see end_byte is read and used before nothing else has written 
in it before. 
This produce different results on different platforms.

Regards
Riccardo

Riccardo Micci
Senior DSP Engineer, Wireless Group 
Cambridge Consultants
Science Park, Milton Road 
Cambridge, CB4 0DW, England
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riccardo.micci at cambridgeconsultants.com
www.CambridgeConsultants.com
 




Jean-Marc Valin <Jean-Marc.Valin at USherbrooke.ca> 
02/09/2010 13:41

To
celt-dev at xiph.org
cc
riccardo.micci at cambridgeconsultants.com
Subject
Re: [CELT-dev] Possible Bug






> The problem comes decoding the next frame. Since now "shortBlocks" is 
false,
> "end_byte" is not initialized anymore and next functions read it before
> update.
>
> Can someone confirm this behaviour? In my case i modified ec_dec_init
> function to initialize it as well. What is the correct value?

Can you give a bit more information on what's happening? The end_byte 
field does not need to be initialized because it should get read when 
end_bits_left is zero. In what function is the uninitialized read 
happening and what happens then?

    Jean-Marc







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