| Date | Tue, 25 Oct 2022 10:22:37 +0200 | From | Pavel Machek <> | Subject | Re: [PATCH 4.19 195/229] drm/amd/display: fix overflow on MIN_I64 definition |
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Hi!
> From: David Gow <davidgow@google.com> > > [ Upstream commit 6ae0632d17759852c07e2d1e0a31c728eb6ba246 ] > > The definition of MIN_I64 in bw_fixed.c can cause gcc to whinge about > integer overflow, because it is treated as a positive value, which is > then negated. The temporary positive value is not necessarily > representable. > > This causes the following warning: > ../drivers/gpu/drm/amd/amdgpu/../display/dc/dml/calcs/bw_fixed.c:30:19: > warning: integer overflow in expression ‘-9223372036854775808’ of type > ‘long long int’ results in ‘-9223372036854775808’ [-Woverflow] > 30 | (int64_t)(-(1LL << 63)) > | ^ > > Writing out (-MAX_I64 - 1) works instead.
While this probably fixes the warning, better fix would be to include limits.h which already has equivalent definitions.
Thanks and best regards, Pavel
> -#define MIN_I64 \ > - (int64_t)(-(1LL << 63)) > - > #define MAX_I64 \ > (int64_t)((1ULL << 63) - 1) > > +#define MIN_I64 \ > + (-MAX_I64 - 1) > + > #define FRACTIONAL_PART_MASK \ > ((1ULL << BW_FIXED_BITS_PER_FRACTIONAL_PART) - 1) > > -- > 2.35.1 > >
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