Re: at2 swap_nibbles

On Mon, Nov 25, 2002 at 07:05:23PM +0100, Andreas Fink wrote:
> how about this: 
> 
> #define	HI_NIBBLE(a)	( (int)a >> 4 & 0x0F) 
> #define	LOW_NIBBLE(a)	( (int)a & 0x0F) 
> #define	SWAP_NIBBLE(a)	(( HI_NIBBLE(a) | (LOW_NIBBLE(a) << 4)) & 0xFF) 
> 
> This would work as a macro and has the advantage that the CPU can run 
> it pretty much native. 

Except that casting to int brings back the original sign-extension bug :)

If swap_nibbles is used only in the at2 driver, then you can make it a
static function and expect the compiler to inline it.  If it's used in
multiple files, then it's better off as a real library function in gwlib
somewhere.  (octstr_swap_nibbles perhaps?)

If you need a really fast nibble swapper, then a table lookup is probably
best.  It'll only be a 256-byte table.  I wouldn't bother with that kind
of optimization unless profiling shows that it matters.

Richard Braakman