linux-kernel - [PATCH 1/2] lib/string.c: Add a macro for memchr

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Date:   Sun, 10 Jul 2022 22:28:21 +0800
From:   Yu-Jen Chang <arthurchang09@...il.com>
To:     andy@...nel.org, akinobu.mita@...il.com
Cc:     jserv@...s.ncku.edu.tw, linux-kernel@...r.kernel.org,
        Yu-Jen Chang <arthurchang09@...il.com>
Subject: [PATCH 1/2] lib/string.c: Add a macro for memchr_inv()

We add a macro MEMCHR_MASK_GEN() so that both memchr_inv()
and memchr() can use it to generate a 8 bytes mask.

Signed-off-by: Yu-Jen Chang <arthurchang09@...il.com>
Signed-off-by: Ching-Chun (Jim) Huang <jserv@...s.ncku.edu.tw>
---
 lib/string.c | 34 ++++++++++++++++++++++++----------
 1 file changed, 24 insertions(+), 10 deletions(-)

diff --git a/lib/string.c b/lib/string.c
index 485777c9d..80469e6c3 100644
--- a/lib/string.c
+++ b/lib/string.c
@@ -879,6 +879,29 @@ char *strnstr(const char *s1, const char *s2, size_t len)
 EXPORT_SYMBOL(strnstr);
 #endif
 
+#if defined(CONFIG_ARCH_HAS_FAST_MULTIPLIER) && BITS_PER_LONG == 64
+
+#define MEMCHR_MASK_GEN(mask) (mask *= 0x0101010101010101ULL)
+
+#elif defined(CONFIG_ARCH_HAS_FAST_MULTIPLIER)
+
+#define MEMCHR_MASK_GEN(mask)                                                  \
+	do {                                                                   \
+		mask *= 0x01010101;                                            \
+		mask |= mask << 32;                                            \
+	} while (0)
+
+#else
+
+#define MEMCHR_MASK_GEN(mask)                                                  \
+	do {                                                                   \
+		mask |= mask << 8;                                             \
+		mask |= mask << 16;                                            \
+		mask |= mask << 32;                                            \
+	} while (0)
+
+#endif
+
 #ifndef __HAVE_ARCH_MEMCHR
 /**
  * memchr - Find a character in an area of memory.
@@ -932,16 +955,7 @@ void *memchr_inv(const void *start, int c, size_t bytes)
 		return check_bytes8(start, value, bytes);
 
 	value64 = value;
-#if defined(CONFIG_ARCH_HAS_FAST_MULTIPLIER) && BITS_PER_LONG == 64
-	value64 *= 0x0101010101010101ULL;
-#elif defined(CONFIG_ARCH_HAS_FAST_MULTIPLIER)
-	value64 *= 0x01010101;
-	value64 |= value64 << 32;
-#else
-	value64 |= value64 << 8;
-	value64 |= value64 << 16;
-	value64 |= value64 << 32;
-#endif
+	MEMCHR_MASK_GEN(value64);
 
 	prefix = (unsigned long)start % 8;
 	if (prefix) {
-- 
2.25.1