| Message ID | 1550124158-1111-1-git-send-email-xiaoxiang@xiaomi.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [V2,1/2] lib/string: add memrchr function | expand |
On Thu, Feb 14, 2019 at 02:02:37PM +0800, Xiang Xiao wrote: > 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. > +void *memrchr(const void *s, int c, size_t n) > +{ > + const unsigned char *p = s + n; > + > + while (n-- != 0) { Simple: while (n--) { > + if ((unsigned char)c == *--p) > + return (void *)p; > + } > + return NULL; > +}
diff --git a/include/linux/string.h b/include/linux/string.h index 7927b87..915c617 100644 --- a/include/linux/string.h +++ b/include/linux/string.h @@ -167,6 +167,9 @@ static inline void memcpy_flushcache(void *dst, const void *src, size_t cnt) memcpy(dst, src, cnt); } #endif +#ifndef __HAVE_ARCH_MEMRCHR +void *memrchr(const void *s, int c, size_t n); +#endif 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..595e0b3 100644 --- a/lib/string.c +++ b/lib/string.c @@ -964,6 +964,29 @@ void *memchr(const void *s, int c, size_t n) EXPORT_SYMBOL(memchr); #endif +#ifndef __HAVE_ARCH_MEMRCHR +/** + * memrchr - Find the last character in an area of memory. + * @s: The memory area + * @c: The byte to search for + * @n: The size of the area. + * + * Return: 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); +#endif + static void *check_bytes8(const u8 *start, u8 value, unsigned int bytes) { while (bytes) {
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 | 3 +++ lib/string.c | 23 +++++++++++++++++++++++ 2 files changed, 26 insertions(+)