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Mon, 18 Aug 2025 11:23:32 -0700 (PDT) From: Jakub Sitnicki To: Nandakumar Edamana Cc: Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , bpf@vger.kernel.org Subject: Re: [PATCH v2 bpf-next] bpf: improve the general precision of tnum_mul In-Reply-To: <20250815140510.1287598-1-nandakumar@nandakumar.co.in> (Nandakumar Edamana's message of "Fri, 15 Aug 2025 19:35:10 +0530") References: <20250815140510.1287598-1-nandakumar@nandakumar.co.in> Date: Mon, 18 Aug 2025 20:23:31 +0200 Message-ID: <87tt24zdy4.fsf@cloudflare.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain On Fri, Aug 15, 2025 at 07:35 PM +0530, Nandakumar Edamana wrote: [...] > @@ -155,6 +163,14 @@ struct tnum tnum_intersect(struct tnum a, struct tnum b) > return TNUM(v & ~mu, mu); > } > > +struct tnum tnum_union(struct tnum a, struct tnum b) > +{ > + u64 v = a.value & b.value; > + u64 mu = (a.value ^ b.value) | a.mask | b.mask; > + > + return TNUM(v & ~mu, mu); > +} > + Not sure I follow. So if I have two tnums that represent known contants, say a=(v=0b1010, m=0) and b=(v=0b0101, m=0), then their union is an unknown u=(v=0b0000, m=0b1111)? Full disclosure - I didn't read through the paper. The routine doesn't seem to appear there, though.