setting a range of variables

AGCB · 2019-12-05 12:09

Will this set a range of bytes

VAR
  byte  flags[7]

PRI  SetFlags     'set flags according to key press
  
  IF din[0] == $01       
    flags[0] := 1       '1st byte = 1
    flags[7-1] := 0     'all other bytes = 0
CON
  'Will this set a range of bytes? Or is there a different way?  (  ..  ) didn't work

Thanks
Aaron

Wuerfel_21 · 2019-12-05 12:12

No, that'll just set flags[6]. I think what you want is

BYTEFILL(@flags[1],0,6)

Look up BYTEFILL in the Propeller manual for details

yisiguro · 2019-12-05 12:20

According to Propeller Manual, It seems that "range-expression" is available for INA, INB, OUTA, OUTB, DIRA, DIRB, and match-expressions in CASE statement.

JonnyMac · 2019-12-05 15:39

You could use just a single byte

  if (din[0] == 1)
    flags := |<0

This will set bit0 of flags and clear the other bits.

AGCB · 2019-12-05 18:02

Looks like BYTEFILL might be the way to set 1 or several bytes but not in one instruction. It may be that I want to set bytes 1 and 4 to one and clear the rest. Probably should clear all 1st then come back and set the one or more to one with however many instructions it takes using bytefill.

I just thought there might be an easier way. I might have to read up on CASE also

Aaron

JonnyMac · 2019-12-05 19:25

Do your flags have to be bytes, or are they always going to be 0 or 1? If they're just binary -- not other values -- then a single byte can hold eight flags and you can set them in one go. For example:

  flags := |<4 | |<1

...will set bits 4 and 1 while clearing the others. Two flags set; six flags cleared; one line of code.

Looks like BYTEFILL might be the way to set 1 or several bytes but not in one instruction.

The bytefill() instruction does set one or many bytes in a single instruction, but they must be the same value.

AGCB · 2019-12-05 19:55

Jon
They only need to be 1 or 0 so that will work fine. I'll experiment with it early tomorrow morning.
Thanks
Aaron

AGCB · 2019-12-05 19:58

Now that I think about it, it's probably way easier than I was trying to do and there are probably other ways to do it too.

JonnyMac · 2019-12-05 20:24

If you're going to be using bit flags, these routine might be useful -- they're from one of my templates.

pub get_bit(value, pos)                                           
                                                            
'' Returns bit (0..1) from pos (0..31) in value                   
                                                                  
  if ((pos => 0) and (pos =< 31))                                 
    return (value >> pos) & 1                                     
  else                                                            
    return 0


pub set_bit(value, pos, bit)

'' Write bit (0..1) to position (0..31) in value

  if (bit)                                                      ' set
    return value | |<pos
  else
    return value & !(|<pos)

Something that I suggest you do to make your code more readable is to create CON masks for your flags.

con

  LIVING_RM = %00000001
  DINING_RM = %00000010
  KITCHEN   = %00000100

This allows you code to make more sense -- when you do things like this

  flags |= LIVING_RM

My point is to be careful using "magic numbers" like I did in my example above. You can still set/clear multiple flags with one line, and make it readable:

  flags := KITCHEN | DINING_RM

You can test with a named flag easily, too:

  if (flags & KITCHEN)
    kitchen_lights(OFF)

setting a range of variables

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