limiting to "no less than" zero

[sayzer]

if buttonB then
 if volume - Vstep >= vstep then
  volume = volume - Vstep
 else
  volume = 0   
 endif
endif

[HankMcSpank]

Straying a little off...

I'm never more than a couple of threads away from having it underlined that I'm still woefully underskilled in this programming melarkey - where's the condition here...

if buttonB then

to my n00b eyes, I'd have thought there should be a condition like "if buttonB = 0 then" or "if buttonB = 1 then"

??

[Ioannis]

If buttonB means If buttonB=1.

Is a default.

A pure boolean logic.

Darrel gets the most elegant so far coding

Ioannis

[HankMcSpank]

I'd figured as much (on account everyone was doing it!)....can the default be changed to 0? (I'd imagine that switches get used with weak pullups or external pullups ....so the switch pressed condition would be a 0).

Re Darrel's entry..

if volume.15 then volume = 0 ; zero if it went negative

how does bit 15 of 'volume' being a '1' indicate negative? Can someone shine a little more light on this one please?

[Ioannis]

Related to the "default" just use the ! before your variable:

If !buttonB then.... meaning If buttonB=0 then...

The 15th bit is the sign bit in two's complement. When the most significant bit is 1, it indicates a negative sign. Just Binary maths...

But is relative. If you use 8-bits then the 8th (most significant bit) is considered the sign bit. As long as you are thinking of positive and negative numbers. So at the end you have from -128 to +127 (1000 0000 to 0111 1111).

http://en.wikipedia.org/wiki/Two's_complement

Ioannis

[Byte_Butcher]

Thanks guys!

Well... I guess the answer to my question is that there isn't really a way that's as easy as using "min" to limit the upper end.

The method that Charles posted is what I've been using. But I was hoping for something that was... simpler.
I guess I'd hoped there was some way as clean and easy as "MAX" but that worked all the way down to zero.

Darrels method using volume.15 is great, but it "wastes" half of a variable.
Most of the variables that I need to limit are declared as bytes, and I need the full 255 step range for some of them.
I *can* use it for my temperature setpoint because that needs a word anyway and I can afford to "lose" part of it.

I'm starting to run low on code space on this project so hoping to find more efficient ways to do a few things...

Thanks for the input!

Steve

[Darrel Taylor]

Darrels method using volume.15 is great, but it "wastes" half of a variable.
Most of the variables that I need to limit are declared as bytes, and I need the full 255 step range for some of them.

With 8-bit values, the CARRY flag is valid after addition or subtraction.

So it can be ...

if buttonB then
    Volume = Volume - Vstep
    IF !STATUS.0 THEN Volume = 0   ; Zero if BORROWED
endif