Messages in this thread | | | Date | Mon, 25 Jun 2018 11:11:57 -0600 | From | Jason Gunthorpe <> | Subject | Re: [PATCH rdma-next 08/12] overflow.h: Add arithmetic shift helper |
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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.
Jason
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