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    SubjectRe: [PATCH 3/5] backlight: pwm_bl: drop use of int_pow()
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    On 08/10/2019 11.31, Daniel Thompson wrote:
    > On Mon, Oct 07, 2019 at 08:43:31PM +0200, Rasmus Villemoes wrote:
    >> On 07/10/2019 17.28, Daniel Thompson wrote:
    >>> On Thu, Sep 19, 2019 at 04:06:18PM +0200, Rasmus Villemoes wrote:
    >>>
    >>> It feels like there is some rationale missing in the description here.
    >>>
    >>
    >> Apart from the function call overhead (and resulting register pressure
    >> etc.), using int_pow is less efficient (for an exponent of 3, it ends up
    >> doing four 64x64 multiplications instead of just two). But feel free to
    >> drop it, I'm not going to pursue it further - it just seemed like a
    >> sensible thing to do while I was optimizing the code anyway.
    >>
    >> [At the time I wrote the patch, this was also the only user of int_pow
    >> in the tree, so it also allowed removing int_pow altogether.]
    >
    > To be honest the change is fine but the patch description doesn't make
    > sense if the only current purpose of the patch is as a optimization.

    Agreed. Do you want me to resend the series with patch 3 updated to read

    "For a fixed small exponent of 3, it is more efficient to simply use two
    explicit multiplications rather than calling the int_pow() library
    function: Aside from the function call overhead, its implementation
    using repeated squaring means it ends up doing four 64x64 multiplications."

    (and obviously patch 5 dropped)?

    Rasmus

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