Re: Rotating through a four-bit nibble

In lugnet.robotics, Jordan Bradford wrote:
> In lugnet.robotics, Geoffrey Hyde wrote:
>> 
>> "Jordan Bradford" <[email protected]> wrote in
>> message news:[email protected]...
>>> In lugnet.robotics, Kevin L. Clague wrote:
>>> Why in the world wouldn't the firmware support shifting? The hardware
>>> <http://www.delorie.com/gnu/docs/binutils/as_236.html certainly does>.
>>> 
>>> Heh, using multiply and divide to simulate shifting is kind of backwards.
>> 
>> The problem is, multiplication and division to a binary CPU, as is the case
>> here, is just a whole series of instructions.
>> 
>> Here is the basic principle explained, partway down the page:
>> 
>> http://www.evergreen.edu/biophysics/technotes/misc/bin_math.htm
>> 
>> A link to binary addition and subtraction, from HowStuffWorks article on
>> binary (it's actually a framed link to a different site, may have to cut out
>> the frame addition if it doesn't work properly), note how it essentially
>> works the same as decimal multiplication/division - also partway down the
>> page.
>> 
>> http://computer.howstuffworks.com/framed.htm?parent=bytes.htm&url=http://www.math.grin.edu/~rebelsky/Courses/152/97F/Readings/student-binary.html
>> 
>> Hope this helps you understand it better!  :)

Kev
> 
> Understand what better? Binary math? No problems with that!

Nice to hear from another bit twiddler....

> 
> By "backwards" I meant that multiplication and division by powers of 2 are
> usually changed to shift L/R by compilers. Also, I am amused that because the
> firmware doesn't use the H8/300's shift instructions for whatever reason,
> people are now trying to write software simulations of a trivial hardware
> operation.

I do find it ironic that the firmware suports bitwise AND and OR, but not XOR,
and also not shifts.  Gack!

Well, at least we're not having to use loops to add things to themselves to
simulate multiplying by a power of two!