Half number decimals Atari assembler

[Grevle]

How to use "half numbers" like 0.2 and 0.5 and 0.8 and so on in Atari assembler ? do i have to create some sort of routine to do that kind of thing ?. Easiest way of setting up routines like that ? 

[Wrathchild]

How do you intend to use them? A staring point would be to read about fixed-point representation

 

But you have alternatives such as using BCD math over a number of bytes and when displaying place a dot before the final digit.

 

Or you can use the floating point package.

 

[StickJock]

For me, from a firmware background, it's easiest to use fixed point numbers.  For example, if you have 16 bits, you might have an 8.8, or a 10.6, or 12.4, depending on how much resolution you need.  For these, instead of a decimal point, you have a binary point.  The bits to the right of the binary point are your fractions.  

 

For base 10 (decimal), you have the tenths place, hundredths place, thousandths place, etc.  For base 2 (binary), you have the halves place, quarters place, eights place, etc.

 

Say that you only need 0..15 and you want to have a resolution of 1/16th.  Then you can use a 4.4 fixed place notation.  So $00 = 0.0 and $88 = 8.5, $C9 = 12.5625 (fraction = 9/16) and $FF = 15.9375 (fifteen and 15/16ths).

Likewise, if you only need .25 increments, you could use a 6.2 notation, the above examples become $00 = 0.0, $88 = 34.0, $C9 = 50.25, $FF = 63.75.