Math

I want to type in a number zero to 6000 and multiply it by .682 and make the result
an integer zero to 4095 to send to a 12 bit D/A. I can't get the math to work???
thank you for your support...
{{          test program
}}
Con                           
_Clkmode = Xtal1 + pll16x       
_Xinfreq = 5_000_000
multi = 0.682
 
Var
   LONG outval        'end count
   long inval        'start count
   LONG oneval
   
Obj
  pst:          "Parallax Serial Terminal"    
 
Pub   main 
     pst.start(115_200)     'check the baud rate
     pst.str(string("hello",$0D))
   
   repeat
           pst.rxflush
           pst.str(string("Gimmie a number --  ",$0D))
           inval:=pst.Decin 
           pst.str(string("got it... your answer is...",$0D))
           outval := inval * multi
           pst.Dec (outval)        
                   

Comments

  • whickerwhicker Posts: 655
    edited 2020-11-05 - 16:59:54
    Spin only natively uses integers. As in whole numbers.

    It would help if you took one step back from how you calculated .682, which can be expressed as a numerator / denominator pair.

    Multiply first, then divide.

    outval := inval * 4095 / 6000
  • Wow! that was E Z... that works fine... I think I missed class that day....

    Thanks Whicker...


    Bill.

  • Or multiply by 1000 you "multi = 0.682" => 682 so you avoid the fractions

    And result "outval := (inval * multi) /1000
  • Duane DegnDuane Degn Posts: 10,341
    edited 2020-11-05 - 17:42:31
    If you want to display decimal values you can use the method "DecPoint" as shown below. If you want three digits after the decimal use 1000 for the value of "denominator".

    This assumes "value" is scaled by the value of "denominator".
    PUB DecPoint(value, denominator)                                             
      
      if value < 0
        Pst.Char("-")
        -value
          
      if value => denominator
        result := value / denominator
        Pst.Dec(result)
        value //= denominator     
      else    
        Pst.Char("0")
      Pst.Char(".")  
      repeat while denominator > 1
        denominator /= 10
        if value => denominator
          result := value / denominator
          Pst.Dec(result)
          value //= denominator
        else
          Pst.Char("0")
    
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