[sdiy] help...no make8() function in Arduino...converting PIC to AVR

[dan snazelle]

On Apr 11, 2012, at 11:53 AM, Ove Ridé wrote:

> On 11 April 2012 17:25, dan snazelle <subjectivity at hotmail.com> wrote:
>> can someone help me ?
>> 
>> i am trying to convert some PIC code to AVR
>> 
>> it is going fine except for 2 things
>> 
>> there is no make8() function and there is no _mul()
>> 
>> 
>> so code lines like this:
>> 
>> 
>> tmp1 = _mul (acc1, val1);
> 
> Do you have a definition of what the function is supposed to do
> exactly? It might help if you could tell me the types of the three
> variables.
> I suspect it's either just an accelerated form of multiplication, or
> multiplication of two bytes which returns the higher byte of the
> answer. Again, some context would be useful.
> You can always try defining a macro so you don't have to edit the code
> in a million places. Something like
> 
> #define _mul(x,y) ((x)*(y))
> 
> or
> 
> #define _mul(x,y) ((x)*(y)>>8)
> 
> Yes, the excessive parentheses are needed in order to guarantee
> correct behavior!
> 
>>  tmpbyte1 = make8(tmp1, 1);
> 
> make8 is apparently a macro/function to pick out a byte from a bigger
> data type. Something like the following should suffice:
> 
> #define make8(val, offset) ( ( (val)>>((offset)*8) ) & 0xFF)
> 
> Again, yes, it sucks in terms of readability to have all those
> parentheses there, but the C preprocessor just does string
> substitution and for example something like 2*make8(1+x,2) would break
> because of operator precedence, without the parentheses.
> 
> But C for PIC8's sucks, and you should probably look into completely
> reorganizing the code if you plan on permanently switching to AVR. AVR
> has much better C support and you don't need as much of these
> architecture specific tricks.
> 
> -- 
> /Ove
> 
> Blog: <http://blog.gg8.se/>
> 
> "Here is Evergreen City. Evergreen is the color of green forever."
> 



OK

from what I can tell

make8 is called whenever there is a 


 static int16 being asked to be converted into a 

  
static int8 




now on AVR an int8 would be a byte I think and an int16 would be an int


the other part of the make8(x,x); is the 2nd variable, usually a 1


so 


   tmpbyte1 = make8(tmp1, 1);




is asking for tmp1 to be somehow mixed with 1 and turned into a byte











for _mul, 

 tmp2 = _mul (acc2, tmpamt);

it is asking for a result  (tmp2) which is in int16 format (so int on an AVR)

the two parameters inside the parentheses are both int8's (bytes)


_mul(int8, int8)


so MAYBE _mul is trying to multiply two bytes into an int???






thanks