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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4b43c17ecdasm10357445e9.5.2026.11.03.14.44.59 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 03 Nov 2026 14:44:59 -0800 (PST) Date: Tue, 3 Nov 2026 22:44:58 +0000 From: David Laight To: Rosalie Fang Cc: Andrew Morton , Kuan-Wei Chiu , Guan-Chun Wu <409411716@gms.tku.edu.tw>, Nathan Chancellor , Bill Wendling , Justin Stitt , Greg Thelen , Yi Zhu , llvm@lists.linux.dev, linux-kernel@vger.kernel.org Subject: Re: [PATCH] lib/base64: fix -Wconstant-conversion warning in INIT_1() Message-ID: <20261103224458.7fdaecd0@pumpkin> In-Reply-To: <20261103163404.159582-1-rosaliefang@google.com> References: <20261103163404.159582-1-rosaliefang@google.com> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Tue, 3 Nov 2026 16:34:04 +0000 Rosalie Fang wrote: > When expanding BASE64_REV_INIT() for v in 0x7c..0x7f (124..127), the > unselected ternary branch (v) - '0' + 52 evaluates to 128..131, which > exceeds SCHAR_MAX (127). Recent Clang versions diagnose implicit integer > constant conversions in unevaluated ternary arms when initializing the > s8 lookup tables: Has that been reported as a compiler bug? > > lib/base64.c:58:18: error: implicit conversion from 'int' to 's8' > (aka 'signed char') changes value from 131 to -125 > [-Werror,-Wconstant-conversion] > 58 | [BASE64_IMAP] = BASE64_REV_INIT('+', ',') > | ^~~~~~~~~~~~~~~~~~~~~~~~~ > lib/base64.c:34:42: note: expanded from macro 'INIT_1' > 34 | : (v) >= '0' && (v) <= '9' ? (v) - '0' + 52 \ > | ~~~~~~~~~~^~~~ > > Explicitly cast the digit-branch expression to s8 to silence the > warning. > > Fixes: c4eb7ad32eab ("lib/base64: optimize base64_decode() with reverse lookup tables") > Assisted-by: LLM > Signed-off-by: Rosalie Fang > --- > lib/base64.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/lib/base64.c b/lib/base64.c > index 325c7332b049..1489c048b1fd 100644 > --- a/lib/base64.c > +++ b/lib/base64.c > @@ -31,7 +31,7 @@ static const char base64_tables[][65] = { > #define INIT_1(v, ch_62, ch_63) \ > [v] = (v) >= 'A' && (v) <= 'Z' ? (v) - 'A' \ > : (v) >= 'a' && (v) <= 'z' ? (v) - 'a' + 26 \ > - : (v) >= '0' && (v) <= '9' ? (v) - '0' + 52 \ > + : (v) >= '0' && (v) <= '9' ? (s8)((v) - '0' + 52) \ > : (v) == (ch_62) ? 62 : (v) == (ch_63) ? 63 : -1 It might save further trouble to put the (s8) cast on the entire RHS expression. David > > /*