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    SubjectRe[2]: [PATCH] fork_init: fix division by zero


    Hello Scott,

    On Wednesday, December 10, 2008 you wrote:

    > On Wed, Dec 10, 2008 at 01:29:12PM +0300, Yuri Tikhonov wrote:
    >> On Wednesday, December 10, 2008 you wrote:
    >> > x * y / z is parsed as (x * y) / z, not x * (y / z).
    >>
    >> Here we believe in preprocessor: since all PAGE_SIZE, 8, and
    >> THREAD_SIZE are the constants we expect it will calculate this.
    >>
    >> E.g. here is the result from this line as produced by cross-gcc
    >> 4.2.2:
    >>
    >> lis r9,0
    >> rlwinm r29,r29,2,16,29
    >> stw r29,0(r9)
    >>
    >> As you see - only rotate-left, i.e. multiplication to the constant.

    > Yes, and also note that it is masking the result by 0xfffc, to preserve
    > the effect of any overflow in (x * y).

    Right, such a mask was the result of missed brackets. Now (see
    "[PATCH][v2] fork_init: fix division by zero" I've just posted) the
    situation is better:

    lis r9,0
    rlwinm r29,r29,2,0,29
    stw r29,0(r9)

    I.e. the mask is 0xFFFFFFFC.

    Regards, Yuri

    --
    Yuri Tikhonov, Senior Software Engineer
    Emcraft Systems, www.emcraft.com



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