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Two's complement

 
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hansw
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Two's complement
PostPosted: Fri Oct 20, 2006 10:59 am     Reply with quote
What is the fastest way to do Two's complement a variable

In this case the parm name is Value

C version. I did not expect so many instructions.
The compiler does not use comf

.................... Value = (!Value) + 1;
154A0: MOVF xC0,F
154A2: BTFSC FD8.2
154A4: GOTO 154AE
154A8: MOVLW 00
154AA: GOTO 154B0
154AE: MOVLW 01
154B0: ADDLW 01
154B2: MOVWF xC0
....................

Is the #asm version correct?
Will this assembly produce the same results ?

.................... #asm
.................... comf Value
154B4: COMF xC0,F
.................... incf Value
154B6: INCF xC0,F
.................... #endasm

Is there a faster way ?

hansw
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Fri Oct 20, 2006 11:37 am     Reply with quote
Quote:

What is the fastest way to do Two's complement a variable
Is there a faster way ?


Do this:
Code:
value = -value;


From the .LST file:
Code:
...... value = -value;
0082:  NEGF   value
Guest
PostPosted: Fri Oct 20, 2006 11:46 am     Reply with quote
PCM programmer wrote:
Quote:

What is the fastest way to do Two's complement a variable
Is there a faster way ?


Do this:
Code:
value = -value;


From the .LST file:
Code:
...... value = -value;
0082:  NEGF   value


Thanks PCM programmer....
That helps, can't get much less than that.
hansw
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