Re: Rotating through a four-bit nibble

In lugnet.robotics, Brian Davis wrote:
> In lugnet.robotics, Kevin L. Clague wrote:
>
>> Since I didn't really complete the assignment I'll try again.
>
>    Both your 1st & 2nd solutions are very good; thanks to you and other posters
> to this thread for giving me a much better handle on binary manipulations, and
> solutions to this problem. In answer to an earlier question, speed is important
> (simple (ie- no loop) maze solving for a line-follower), but so is size because
> this program is getting long fast. I'd like an entry for the ChiBots event which
> is a maze of 7x7 potential nodes, so bit representations for some things are
> going to save some variable space. As well as being a more "natural" way of
> doing it.
>
>> I confirmed that even SDK v2.5 does not have shifts
>> or rotates
>
>    I guess I shouldn't have been too surprised by this - after all, it's aimmed
> at programming for kids, so such "low level" operations aren't going to be used
> very often (at all). Still, bit of a surprise - I was assuming I should use the
> shift operator for speed. Oh well.
>
>    Now I need to figure out good ways to code all this (I've almost got the
> movement and detection routines polished, and the mechanical aspects were easy
> (because I'm reusing an older platform). Now I'm bumbing up against the memory &
> speed limitations of the standard firmware (but it's taken me something like
> four years to get there, so I'm not complaining).

Maybe it is time to move on to BrickOS?

int
rotate_right(
  int value,   // the value to be rotated
  int width,   // the width of the rotated field
  int base,    // bitnumber of rightmost bit in rotate field
  int amount)  // the amount to rotate between base and base+width)
{
  int r,l;
  r = value >> amount;
  l = value << width - amount;
  r &= (1 << (base + amount)) - (1 << base);
  l &= (1 << (base + width)) - (1 << (base + amount));
  value &= ~((1 << (base + width)) - (1 << base);
  value |= r | l;
}

Kev