faster way to implement a circular buffer

Oli Filth wrote:

> robert bristow-johnson said the following on 02/09/2006 15:46:
>> 
>> Hans S�rensen wrote:
>> 
>>> Right now it's implemented like this (but it's slooooooooow):
>> 
>> that's because "%" is often as slow as "/".
>> 
>>>    CyclicCounter=CyclicCounter%256;
> ...
>> in general, for C, the faster way is to mask:
>> 
>>     CyclicCounter=CyclicCounter&0xFF;
> 
> Wouldn't a decent compiler perform this sort of optimisation
> automatically?  (Just as it might optimise x/2 to x>>1, etc.).
> 

On Blackfin, VisualDSP would (or should) automagically set-up and use a
circular buffer when '%' is used. Or at least if the 'CyclicCounter' would
be the counter in for-loop instead of 'i' (I don't know how naive the
compiler is).

In addition there is pragmas or instrics in VisualDSP++ which can be used to
tell the compiler to generate a circular buffer for the given for-loop.

-- 
Jani Huhtanen