linux-kernel - [PATCH v1 5/5] hash.h: Silence a clang -Wshorten-64-to-32 warning

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Message-ID: <20250403165702.396388-6-irogers@google.com>
Date: Thu,  3 Apr 2025 09:57:02 -0700
From: Ian Rogers <irogers@...gle.com>
To: Yury Norov <yury.norov@...il.com>, Rasmus Villemoes <linux@...musvillemoes.dk>, 
	Arnd Bergmann <arnd@...db.de>, Nathan Chancellor <nathan@...nel.org>, 
	Nick Desaulniers <nick.desaulniers+lkml@...il.com>, Bill Wendling <morbo@...gle.com>, 
	Justin Stitt <justinstitt@...gle.com>, Ian Rogers <irogers@...gle.com>, 
	Adrian Hunter <adrian.hunter@...el.com>, Thomas Gleixner <tglx@...utronix.de>, 
	Jakub Kicinski <kuba@...nel.org>, Jacob Keller <jacob.e.keller@...el.com>, linux-arch@...r.kernel.org, 
	linux-kernel@...r.kernel.org, llvm@...ts.linux.dev
Subject: [PATCH v1 5/5] hash.h: Silence a clang -Wshorten-64-to-32 warning

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@...gle.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