Re: [avr-gcc-list] Cicrular Buffer routines

[Dave Hylands]

Hi Bob,

> You can test to make sure that you do have a power of two buffer size with the
> following:
>
> #define myQ_SIZE    64
>
> #define myQ_MASK ( myQ__SIZE - 1 )
> #if ( myQ__SIZE & myQ__MASK )
>  #error myQ_SIZE buffer size is not a power of 2
> #endif
>
> The effect is to check if only one, and only one, bit is set in myQ_SIZE.

Good point. I think I would refine things slightly like this:

#define CBUF_Size( cbuf )    ( sizeof( cbuf.m_entry ) / sizeof(
cbuf.m_entry[ 0 ] ))

and replace all occurences of cbuf##_SIZE with CBUF_Size( cbuf )
You now no longer need the myQ_SIZE macro.

Then add:

#define CBUF_SizeIsPowerOf2( cbuf ) (( CBUF_Size( cbuf ) & (
CBUF_Size( cbuf ) - 1 )) == 0 )

Then for each circular buffer you create, you can throw in a variant of:

#if ( !CBUF_SizeIsPowerOf2( myQ ))
#    error size of myQ not a power of 2
#endif

-- 
Dave Hylands
Vancouver, BC, Canada
http://www.DaveHylands.com/