Which conditional expression is faster?

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  1. - 15th February 2009, 13:47 #4
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    Quote Originally Posted by RussMartin View Post
    Which of these is faster to execute?

    IF A+B+C=0 THEN . . .

    or

    IF A=0 AND B=0 AND C=0 THEN . . .

    Hi, RUSS

    A+B+C = 0 has many solutions AS ... you use an ADDITION and not a Bitwise AND !!!

    253 + 2 + 1 = 0 .... for Bytes !!!
    1 + 1 + 0 = 0 ... for Bits !!!

    so, It can't be equivalent to the second line ... Too Bad !


    Now, let's suppose A, B, C are BITs ...



    so

    Code:
    IF  A | B | C  THEN Z = 1...
    Will be the fastest ... with PBP.`( 17 asm Lines ...)

    Code:
    IF  (NOT A & NOT B & NOT C ) THEN Z = 1
    is somewhat longer ...

    BUT, if A,B,C are inputs ... would be faster to mask the other inputs and test if result is 0

    Code:
    IF ( PORTx & %00000111 ) THEN Z = 1
    Only 12 asm lines ...

    Alain
    Last edited by Acetronics2; - 15th February 2009 at 20:46.
    ************************************************** ***********************
    Why insist on using 32 Bits when you're not even able to deal with the first 8 ones ??? ehhhhhh ...
    ************************************************** ***********************
    IF there is the word "Problem" in your question ...
    certainly the answer is " RTFM " or " RTFDataSheet " !!!
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