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    SubjectRe: [PATCH] Multiple & vs. && and | vs. || bugs in 2.4.20
    Ulrich Drepper wrote:
    > > - if (!urb->status & !acm->throttle) {
    > > + if (!urb->status && !acm->throttle) {
    > Have you really looked at detail at all these cases? The problem is
    > that you have made the code less efficient on some platforms. The use
    > of && requires shortcut evaluation. I.e., the compiler is forced to not

    While I agree with your observation in general, this is actually
    something the compiler should be able to figure out by itself:

    - there's only a side-effect if acm is NULL
    - in ACM_READY, we've already tested acm for NULL, and subsequently
    de-referenced it
    - acm is a local variable, and not aliased, so the dbg() can't
    change it

    So, given the negations, || and | are equivalent in this case, and
    whether a jump, conditional execution, a bit operation, or something
    else yields better code is compiler, machine, and context specific.

    - Werner

    / Werner Almesberger, Buenos Aires, Argentina /
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      Last update: 2005-03-22 13:33    [W:0.021 / U:23.532 seconds]
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