Can I combine bitwise '&' with CASE?

lardom · 2016-01-20 17:45

I want to use bits 0-3 to pass a value and bits 4-7 to point to specific variables in an object that recieves values wirelessly.
I have in mind four variables, let's call them A, B, C and D. I want to point to them like this:
%0001_xxxx (copy to variable a)
%0010_xxxx (copy to variable b)
%0011_xxxx (copy to variable c)
%0100_xxxx (copy to variable d)
I really want to eliminate a lot of IF statements.

Electrodude · 2016-01-20 17:54

lardom wrote: »

I want to use bits 0-3 to pass a value and bits 4-7 to point to specific variables in an object that recieves values wirelessly.
I have in mind four variables, let's call them A, B, C and D. I want to point to them like this:
%0001_xxxx (copy to variable a)
%0010_xxxx (copy to variable b)
%0011_xxxx (copy to variable c)
%0100_xxxx (copy to variable d)
I really want to eliminate a lot of IF statements.

Yes, the argument to a case can be any expression.

PUB foo(x)

  case x & %1111_0000
    %0001_0000:
      ' a
    %0010_0000:
      ' b
    %0011_0000:
      ' c
    %0100_0000:
      ' d
    other:
      ' invalid

You can even put an assignment operation there if you like, such as "x++" or "x *= 23"

lardom · 2016-01-20 18:37

Electrodude, thank you!

lardom · 2016-01-20 23:26

Electrodude, it compiled. I sat there admiring it. It's not in it's final form but it'll clearly do what I want it to. Thanks again.

case CurrentSpeed & %1111_0000
   %0001_0000  : front_left  := CurrentSpeed - %0001_0000
   %0010_0000  : front_right := CurrentSpeed - %0010_0000 
   %0011_0000  : back_left   := CurrentSpeed - %0011_0000
   %0100_0000  : back_right  := CurrentSpeed - %0100_0000

Electrodude · 2016-01-20 23:44

lardom wrote: »
Electrodude, it compiled. I sat there admiring it. It's not in it's final form but it'll clearly do what I want it to. Thanks again.
case CurrentSpeed & %1111_0000
   %0001_0000  : front_left  := CurrentSpeed - %0001_0000
   %0010_0000  : front_right := CurrentSpeed - %0010_0000 
   %0011_0000  : back_left   := CurrentSpeed - %0011_0000
   %0100_0000  : back_right  := CurrentSpeed - %0100_0000

I would recommend that you instead write:

case CurrentSpeed & %1111_0000
   %0001_0000  : front_left  := CurrentSpeed & %1111
   %0010_0000  : front_right := CurrentSpeed & %1111
   %0011_0000  : back_left   := CurrentSpeed & %1111
   %0100_0000  : back_right  := CurrentSpeed & %1111

or even:

value := CurrentSpeek & %1111
case CurrentSpeed & %1111_0000
   %0001_0000  : front_left  := value
   %0010_0000  : front_right := value
   %0011_0000  : back_left   := value
   %0100_0000  : back_right  := value

That way, you won't need to change the same thing in two places if you want to change the top part constant or add more cases.

lardom · 2016-01-21 00:36

I'm gonna take a look at it on the Propeller tool. I'm not out of the woods by a long shot. I'm going to test what I've written in maybe two days. I still have some things to work out.
I was successfully able to control the speed of one motor EDIT: (with a joystick) foward and reverse using the nrf24L01 transceiver.
Wireless control of two motors differentially is a major jump (for me) because of the 8-bit bottleneck.
1)Rotate left/right
2)turn left/right forward
3)turn left/right backward
I also want to add pan/tilt for a camera and an arm with a gripper.

Can I combine bitwise '&' with CASE?

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