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From: Ian Rogers <irogers@google.com>
To: Yury Norov <yury.norov@gmail.com>,
	Rasmus Villemoes <linux@rasmusvillemoes.dk>,
	 Arnd Bergmann <arnd@arndb.de>,
	Nathan Chancellor <nathan@kernel.org>,
	 Nick Desaulniers <nick.desaulniers+lkml@gmail.com>,
	Bill Wendling <morbo@google.com>,
	 Justin Stitt <justinstitt@google.com>,
	Ian Rogers <irogers@google.com>,
	 Adrian Hunter <adrian.hunter@intel.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	 Jakub Kicinski <kuba@kernel.org>,
	Jacob Keller <jacob.e.keller@intel.com>,
	linux-arch@vger.kernel.org,  linux-kernel@vger.kernel.org,
	llvm@lists.linux.dev
Subject: [PATCH v1 5/5] hash.h: Silence a clang -Wshorten-64-to-32 warning
Date: Thu,  3 Apr 2025 09:57:02 -0700	[thread overview]
Message-ID: <20250403165702.396388-6-irogers@google.com> (raw)
In-Reply-To: <20250403165702.396388-1-irogers@google.com>

The clang warning -Wshorten-64-to-32 can be useful to catch
inadvertent truncation. In some instances this truncation can lead to
changing the sign of a result, for example, truncation to return an
int to fit a sort routine. Silence the warning by making the implicit
truncation explicit.

Signed-off-by: Ian Rogers <irogers@google.com>
---
 include/linux/hash.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/hash.h b/include/linux/hash.h
index 38edaa08f862..ecc8296cb397 100644
--- a/include/linux/hash.h
+++ b/include/linux/hash.h
@@ -75,7 +75,7 @@ static __always_inline u32 hash_64_generic(u64 val, unsigned int bits)
 {
 #if BITS_PER_LONG == 64
 	/* 64x64-bit multiply is efficient on all 64-bit processors */
-	return val * GOLDEN_RATIO_64 >> (64 - bits);
+	return (u32)(val * GOLDEN_RATIO_64 >> (64 - bits));
 #else
 	/* Hash 64 bits using only 32x32-bit multiply. */
 	return hash_32((u32)val ^ __hash_32(val >> 32), bits);
-- 
2.49.0.504.g3bcea36a83-goog


      parent reply	other threads:[~2025-04-03 16:57 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2025-04-03 16:56 [PATCH v1 0/5] Silence some clang -Wshorten-64-to-32 warnings Ian Rogers
2025-04-03 16:56 ` [PATCH v1 1/5] bitfield: Silence a clang -Wshorten-64-to-32 warning Ian Rogers
2025-04-03 16:56 ` [PATCH v1 2/5] bitmap: " Ian Rogers
2025-04-04  5:49   ` Arnd Bergmann
2025-04-04 11:31     ` Ian Rogers
2025-04-03 16:57 ` [PATCH v1 3/5] bitops: " Ian Rogers
2025-04-04  5:43   ` Arnd Bergmann
2025-04-04 11:35     ` Ian Rogers
2025-04-03 16:57 ` [PATCH v1 4/5] math64: " Ian Rogers
2025-04-03 16:57 ` Ian Rogers [this message]

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