How do we in Spine declare a signed variable?

EMHmark7

Hi,

I want to declare a Spine variable that will hold negative values (-127 to 127 is enough).

Doc says how to "sign" a variable in a formula,
1) but what is the right way to get a variable that will hold a negative value while not in calculations?

2) Do we need to convert somehow when we do calculations along with unsigned bytes?

Thanks
Marc

Heater.

All variables in the Spin language are signed.
The problem might come when you want them not to be signed.

Ariba

Actually, all long variables are treated as signed, but word- and byte-variables as unsigned.

But you can store signed values also in word and byte variables, without special declaration. Spin does all internal calculation with signed 32bit, so you need to tell Spin if a word or byte variable holds a signed value, when it accesses the variable (and expands it to a 32bit value):

 VAR
  byte val1

PUB
  val1 := -3
  longvar := val1    'you get 253  (256-3)
  longvar := ~val1   'you get -3

  val1 := 253
  longvar := val1    'you get 253
  longvar := ~val1   'you get -3

Andy

EMHmark7

Thanks for reply,

But when I do x:=x-1 when x was 0, I got in the 255, 254, etc.

Doc specify necessity to use the ~x for getting good results if the variable holds a negative value.

1) So, now I suppose all Long and up are signed.
So, I would just need to declare as Long.

2) so, about a signed byte, can we do this ~x:= ~x-1
in ordert to store the signe value?

Anybody can confirm that?

Thanks,
Marc

EMHmark7

I saw Speedy Gonsalez's reply after I posted my comment, Arrrriba, Arrrrriba!

So, I catch that Spine will save the signed value in the byte without need for declaring signed,
but would need the tilde when "reading" that variable in order to get the right value.

Anybody tell me if I am misled on that.

Thanks,
I am going to try it right now.

Ariba

EMHmark7 wrote: »

But when I do x:=x-1 when x was 0, I got in the 255, 254, etc.

How do you know that it is 255,254... and not -1, -2... that is just a definition.

If you print the value out you can use: ser.dec(x) and will get 255, or ser.dec(~x) and will get -1.

[1) So, now I suppose all Long and up are signed.
So, I would just need to declare as Long.

2) so, about a signed byte, can we do this ~x:= ~x-1
in ordert to store the signe value?

Anybody can confirm that?

[/SIZE][/SIZE]

1) yes, that is the easiest and best solution. Byte and Word ariables makes only sense for big arrays to spare ram, but not for single variables which you use in calculations.

2) I think this will not work

Andy