Phil wrote:
> Hello everyone,
>
> With a bit more thought I was able to solve my previous question, however
the
> answer to this next question is beyond a simple beginner.
>
> I need assembly code to solve this formula:
>
> angle = a + (b * count)
>
> where
>
> a = 82.9
> b = -0.2
> count is a ten bit integer
> angle is also an integer, so I have to add on .5 to the result
>
> I've been to the Microchip site where I found a lot of documents that
discuss
> floating point maths but no code examples.
>
> Can someone please help?
>

The best way to do this (in code space, complexity, and running time) is to
use fixed point math (integers) for the entire calculation.  Simply use
values ten times what they need to be, and make the correction in your head.

This gives: angle = 892 - 2*count

Just multiply count by 10 before putting it into the calculation.  The
multiplication by 2 is equivalent to a bit shift to the left on count, and
16 bit integer subtraction is significantly easier than floating point
subtraction.  Angle will then be exactly ten times the answer you are
looking for, so you then change the code that uses angle to expect a value
in that range.

So, instead of a bunch of floating point math, you have a multiplication, a
bitshift, and a subtraction.  Unless something else prevents you from doing
it this way, things will be a lot easier.

Daniel Imfeld

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