Working out a decimal percentage for display

[h0ffman]

Me again!

I'm trying to work out the percentage difference between two numbers so that it can be displayed as, for example, +%040 on screen.

I've already got a the decimal conversion, the problem is working out the actual value.

I tried the following..

move.w #120,d0
move.w #90,d1
divu d1,d0

on a calculator it comes out as 1.333333... which is a 33% increase. However i'm simply left with 1 and the remainder in the upper half of the data register.

It also needs to deal with the calculation the other way, i.e. show a negative percentage.

Any help would be awesome.

[demolition]

If you want two decimals, you could do the following in pseudo-code using integer math:

If Num1>Num2
Result = Num1*100 / Num2 - 100
else
Result = -(Num2*100 / Num1 - 100)

[hooverphonique]

move #original value,d1
move #new value, d0
sub d1, d0
muls #100,d0
divs d1,d0


if you do that with your example above, d0 will now be -25 (90 is 120-25%).

[h0ffman]

Originally Posted by hooverphonique

move #original value,d1
move #new value, d0
sub d1, d0
muls #100,d0
divs d1,d0


if you do that with your example above, d0 will now be -25 (90 is 120-25%).

Perfect!! thats actually the same data registers I'm using too!!

[demolition]

Originally Posted by hooverphonique

if you do that with your example above, d0 will now be -25 (90 is 120-25%).

True, my example was faulty as it did not calculate that correctly, so ignore what I wrote.

[hooverphonique]

Originally Posted by h0ffman

Perfect!! thats actually the same data registers I'm using too!!

Yeah.. I did that on purpose

[h0ffman]

Well this has been a learning experience, only just realised there is a MULS and MULU! Signed and unsigned. I really need to read the 68000 manual again!

All good now, got it working