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    SubjectRe: [PATCH rdma-next 08/12] overflow.h: Add arithmetic shift helper
    On Mon, Jun 25, 2018 at 11:11:57AM -0600, Jason Gunthorpe wrote:
    > On Mon, Jun 25, 2018 at 11:26:05AM +0200, Rasmus Villemoes wrote:
    >
    > > check_shift_overflow(a, s, d) {
    > > unsigned _nbits = 8*sizeof(a);
    > > typeof(a) _a = (a);
    > > typeof(s) _s = (s);
    > > typeof(d) _d = (d);
    > >
    > > *_d = ((u64)(_a) << (_s & (_nbits-1)));
    > > _s >= _nbits || (_s > 0 && (_a >> (_nbits - _s -
    > > is_signed_type(a))) != 0);
    > > }
    >
    > Those types are not quite right.. What about this?
    >
    > check_shift_overflow(a, s, d) ({
    > unsigned int _nbits = 8*sizeof(d) - is_signed_type(d);
    > typeof(d) _a = a; // Shift is always performed on type 'd'
    > typeof(s) _s = s;
    > typeof(d) _d = d;
    >
    > *_d = (_a << (_s & (_nbits-1)));
    >
    > (((*_d) >> (_s & (_nbits-1)) != _a);
    > })
    >
    > And can we use mathamatcial invertability to prove no overlow and
    > bound _a ? As above.

    Rasmus and Jason,

    Thanks for the feedback.
    The reason why I introduced function, because wanted to reuse
    check_mul_overflow macro, but for any reasons which I don't remember
    now, I had hard time to fix compilation errors.

    Anyway, I'll resubmit.

    Thanks


    >
    > Jason
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