From: Xiang Xiao <xiaoxiang781216@gmail.com>
To: gregkh@linuxfoundation.org, alexander.shishkin@linux.intel.com,
andriy.shevchenko@linux.intel.com, linux-kernel@vger.kernel.org
Cc: Xiang Xiao <xiaoxiang@xiaomi.com>
Subject: [v2] lib/string: add memrchr function
Date: Wed, 13 Feb 2019 02:54:43 +0800 [thread overview]
Message-ID: <1549997683-27986-1-git-send-email-xiaoxiang@xiaomi.com> (raw)
In-Reply-To: <1549994809-27479-1-git-send-email-xiaoxiang@xiaomi.com>
Here is the detailed description for memrchr:
void *memrchr(const void *s, int c, size_t n);
The memrchr() function is like the memchr() function, except
that it searches backward from the end of the n bytes pointed
to by s instead of forward from the beginning.
The memrchr() functions return a pointer to the matching byte
or NULL if the character does not occur in the given memory
area.
Signed-off-by: Xiang Xiao <xiaoxiang@xiaomi.com>
---
include/linux/string.h | 1 +
lib/string.c | 21 +++++++++++++++++++++
2 files changed, 22 insertions(+)
diff --git a/include/linux/string.h b/include/linux/string.h
index 7927b87..f380f4b 100644
--- a/include/linux/string.h
+++ b/include/linux/string.h
@@ -167,6 +167,7 @@ static inline void memcpy_flushcache(void *dst, const void *src, size_t cnt)
memcpy(dst, src, cnt);
}
#endif
+void *memrchr(const void *s, int c, size_t n);
void *memchr_inv(const void *s, int c, size_t n);
char *strreplace(char *s, char old, char new);
diff --git a/lib/string.c b/lib/string.c
index 38e4ca0..92914f6 100644
--- a/lib/string.c
+++ b/lib/string.c
@@ -964,6 +964,27 @@ void *memchr(const void *s, int c, size_t n)
EXPORT_SYMBOL(memchr);
#endif
+/**
+ * memrchr - Find a character in an area of memory.
+ * @s: The memory area
+ * @c: The byte to search for
+ * @n: The size of the area.
+ *
+ * returns the address of the last occurrence of @c, or %NULL
+ * if @c is not found
+ */
+void *memrchr(const void *s, int c, size_t n)
+{
+ const unsigned char *p = s + n;
+
+ while (n-- != 0) {
+ if ((unsigned char)c == *--p)
+ return (void *)p;
+ }
+ return NULL;
+}
+EXPORT_SYMBOL(memrchr);
+
static void *check_bytes8(const u8 *start, u8 value, unsigned int bytes)
{
while (bytes) {
--
2.7.4
next prev parent reply other threads:[~2019-02-12 18:55 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-12 18:06 [PATCH] lib/string: add memrchr function Xiang Xiao
2019-02-12 18:34 ` Greg KH
2019-02-12 19:09 ` xiang xiao
2019-02-12 19:15 ` Greg KH
2019-02-12 19:22 ` xiang xiao
2019-02-12 18:54 ` Xiang Xiao [this message]
2019-02-12 19:11 ` [v2] " Greg KH
2019-02-12 19:12 ` Greg KH
2019-02-12 19:19 ` xiang xiao
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