setting values and percentages

[richard]

I wrote this little bit of code to experiment with this thread its interesting to note that to */ method fails when your percentage goes past 1600 in lieu of 50
but the div32 method is quit sound up until the result exceeds 2^16 (65535 )
you need to remember that */ is the middle 16 bits and if you overflow that your still in trouble

****************************************************************
'*  Name    : UNTITLED.BAS                                      *
'*  Author  : [select VIEW...EDITOR OPTIONS]                    *
'*  Notice  : Copyright (c) 2014 [select VIEW...EDITOR OPTIONS] *
'*          : All Rights Reserved                               *
'*  Date    : 7/2/2014                                          *
'*  Version : 1.0                                               *
'*  Notes   : 16f684                                                  *
'*          :                                                   *
'****************************************************************
  
#CONFIG
     __config _INTRC_OSC_NOCLKOUT & _CP_OFF & _WDT_ON  &  _PWRTE_ON  &  _MCLRE_OFF 
#ENDCONFIG
 include "alldigital.pbp"
 
 
 
 
 
 
              OPTION_REG.7=0
              trisa = %11111110
             
              DEFINE OSC 4
              so var porta.0
              dq var portc.1
              Nposn var word
              ss var word
              s2 var word    
              s1 var word
              
               
    high so         
    ss=4095 
    s1=1600
    s2=100      
         
    pause 4000       
    serout2 so,84,[ "ready ",13,10] 
    lop: 
    pause 2000
    nposn=s1*ss
    nposn = div32 s2          
    serout2 so,84,["1 " ,#Nposn,13,10   ]   
    nposn=1600*4095/100          ; you need to adjust this line too
    serout2 so,84,["2 " ,#Nposn,13,10   ]
    nposn =  s1  */ 10484
    serout2 so,84,["3 ", #Nposn,13,10   ]
    nposn=s1*ss/100
    serout2 so,84,["4 ", #Nposn,13,10   ] 
    
    goto lop

[EarlyBird2]

the div32 method is quit sound up until the result exceeds 2^16 (65535 )
you need to remember that */ is the middle 16 bits and if you overflow that your still in trouble

Is this because of the word variable being used?
Is this different in PBPL?

[richard]

yes only because the result needs to fit a word var


all of this only applies to pbpw only , pbpl is another story

[EarlyBird2]

no its not because of the word var its just the way */ works .

all of this only applies to pbpw only , pbpl is another story

Yes */ can only result in a word the same applies to DIV32 in PBP2.xx as LONGs are not supported.

PBP3 supports LONG variables and */ returns the top 32 bits of a 48 bits internal result, ignoring the lower 16 bits or dividing by 65536 which ever you prefer.

[HenrikOlsson]

Hi,

With PBPW a multiplication results in an internal 32bit result. The */ operator returns the middle 16 bits (inherent division by 256) while the ** operator returns the top 16bits (inherent division by 65536) of this 32bit intermediate result. You need a WORD variable to accommodate the "full" result.

With PBPL a multiplication results in an internal 48bit result. The */ operator returns the middle 32 bits (inherent division by 256) while the ** operator returns the top 32bits (inherent division by 65536) of this 48bit intermediate result. You need a LONG variable to accommodate the full result.

Yes */ can only result in a word the same applies to DIV32 in PBP2.xx as LONGs are not supported.

You don't need PBP3 to use LONGs. Support for that was introduced in PBP2.50, 7 years ago. But you DO need to use an 18F part.

And, finally, DIV32 isn't supported (not needed) with PBPL since it uses a 32bit division routine by default.

All this according to the manual.

EDIT: Both the */ and ** operators supports variables on both sides of the operator while DIV32 requires a constant on the right side. You can't do

Dummy = 1000*1000
Result = DIV32 myVAR   ' Won't work, DIV32 requires division by a constant.

EDIT again, about that DIV32 requiring a constant.....I'm not sure any more. Must try it on actual hardware so you may want to disregard that for the moment :-)

/Henrik.

[HenrikOlsson]

Aargh, not allowed to edit my post....
Regarding the DIV32 - I was wrong, it's more the other way around. Doing Dummy = 1000*1000 won't work because both are constants. At least one of the vaules must be a variable or the compiler will replace the multiplication with a constant resulting in the internal system variables not containing the value for DIV32 to operate on. See here and here for more details.

Sorry for the mixup in my previous reply.

/Henrik.