opus - Mar 2011 - Bitrev for FFT

Hi,
Our DSP has a built-in bitrev instruction so we're exploring the 
possibility of calculating the bitrev every time instead of filling the 
table during initialisation, hence saving some memory.

Our frame size is fixed to 320 samples. The two FFTs sizes for normal 
block and short block are 160 and 40 respectively. It's not really clear 
how the function "compute_bitrev_table" calculates the values.
Could you quickly explain the idea behind the function so we can try to 
implement it on the fly?

Regards
Riccardo


Riccardo Micci
Senior DSP Engineer, Wireless Group 
Cambridge Consultants
Science Park, Milton Road 
Cambridge, CB4 0DW, England
Switchboard: +44 (0)1223 420024
Direct dial: +44 (0)1223 392402
Mobile: +44 (0)
Fax: +44 (0)1223 423373
riccardo.micci at cambridgeconsultants.com
www.CambridgeConsultants.com
 





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I'd be *very* surprised if your DSP's bitrev instruction worked for 
sizes that are non-powers of two, so you should probably stick with the 
table.

	Jean-Marc

On 11-03-03 06:42 AM, Riccardo Micci wrote:
>
> Hi,
> Our DSP has a built-in bitrev instruction so we're exploring the
> possibility of calculating the bitrev every time instead of filling the
> table during initialisation, hence saving some memory.
>
> Our frame size is fixed to 320 samples. The two FFTs sizes for normal
> block and short block are 160 and 40 respectively. It's not really
clear
> how the function "compute_bitrev_table" calculates the values.
> Could you quickly explain the idea behind the function so we can try to
> implement it on the fly?
>
> Regards
> Riccardo
> ------------------------------------------------------------------------
>
> Riccardo Micci
> Senior DSP Engineer, Wireless Group
>
> *Cambridge Consultants*
> Science Park, Milton Road
> Cambridge, CB4 0DW, England
> Switchboard: +44 (0)1223 420024
> Direct dial: +44 (0)1223 392402
> Mobile: +44 (0)
> Fax: +44 (0)1223 423373
> riccardo.micci at cambridgeconsultants.com
> <mailto:riccardo.micci at cambridgeconsultants.com>
> www.CambridgeConsultants.com <http://www.cambridgeconsultants.com/>
>
>
>
>
>
> ------------------------------------------------------------------------
>
>
> This email is from Cambridge Consultants Limited, Science Park, Milton
> Road, Cambridge CB4 0DW with registered number 1036298 England. It may
> contain confidential information. It is intended for the addressee only
> and may not be copied or disclosed to any third party without our
> permission. If you are not the intended recipient please contact the
> sender as soon as possible and delete the material from any computer. If
> this email has been sent as a personal message to the addressee, the
> sender is not acting in his/her capacity as an employee or officer of
> Cambridge Consultants Limited and no liability is accepted for the
> content of any such email. Outgoing email may be monitored for the
> purpose of ensuring compliance with our email policy and relevant laws.
>
>
>
>
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