Terry Harris escreveu:
> On Fri, 03 Jul 2009 20:14:13 -0300, you wrote:
>
>
>> OK, explain this under this theory:
>>
>> Look how they do 'Var = 0;' :
>>
>> bcf STATUS,C
>> *movlw* 0
>> btfsc STATUS,C
>> *movlw* 1
>> movwf Var
>>
>
> Evaluate the right hand expression and put the result in something just big
> enough (in this case the carry flag). Copy the result to the lvalue.
>
Makes absolutely no sense. It is testing something itself set hard
coded. And there are two movlw, the expression doesn't have any
conditionals.
>> 'Var = 1;'
>>
>> clrf Var
>> bsf STATUS,C
>> rlf Var,f
>>
>
> Same again although I don't know why it chose a different method to copy.
Just to grow the code, perhaps?
>> 'Var = 2;'
>>
>> clrw
>> iorlw 2
>> movwf Temp
>> movf Temp,w
>> movwf Var
>>
>
> Same again but the expression needs a file to hold the result.
>
> It seems the compiler is being smart recognising constant expressions of 0
> and 1 will fit in a bit and treating them differently. The generated code
> looks dumb but I presume provides more scope of optimisation by the bit of
> the compiler you didn't buy.
>
The temporary location seems reasonable in unoptimized code, but why
load w in a such awkward way?
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