[PATCH 05/25] tools lib: Adopt memchr_inv() from kernel

Jiri Olsa
2020-11-26T17:01:30Z

We'll use it to check for undefined/zero data.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
tools/include/linux/string.h | 1 +
tools/lib/string.c | 58 ++++++++++++++++++++++++++++++++++++
2 files changed, 59 insertions(+)

diff --git a/tools/include/linux/string.h b/tools/include/linux/string.h
index 5e9e781905ed..db5c99318c79 100644
--- a/tools/include/linux/string.h
+++ b/tools/include/linux/string.h
@@ -46,4 +46,5 @@ extern char * __must_check skip_spaces(const char *);

extern char *strim(char *);

+extern void *memchr_inv(const void *start, int c, size_t bytes);
#endif /* _TOOLS_LINUX_STRING_H_ */
diff --git a/tools/lib/string.c b/tools/lib/string.c
index f645343815de..8b6892f959ab 100644
--- a/tools/lib/string.c
+++ b/tools/lib/string.c
@@ -168,3 +168,61 @@ char *strreplace(char *s, char old, char new)
*s = new;
return s;
}
+
+static void *check_bytes8(const u8 *start, u8 value, unsigned int bytes)
+{
+ while (bytes) {
+ if (*start != value)
+ return (void *)start;
+ start++;
+ bytes--;
+ }
+ return NULL;
+}
+
+/**
+ * memchr_inv - Find an unmatching character in an area of memory.
+ * @start: The memory area
+ * @c: Find a character other than c
+ * @bytes: The size of the area.
+ *
+ * returns the address of the first character other than @c, or %NULL
+ * if the whole buffer contains just @c.
+ */
+void *memchr_inv(const void *start, int c, size_t bytes)
+{
+ u8 value = c;
+ u64 value64;
+ unsigned int words, prefix;
+
+ if (bytes <= 16)
+ return check_bytes8(start, value, bytes);
+
+ value64 = value;
+ value64 |= value64 << 8;
+ value64 |= value64 << 16;
+ value64 |= value64 << 32;
+
+ prefix = (unsigned long)start % 8;
+ if (prefix) {
+ u8 *r;
+
+ prefix = 8 - prefix;
+ r = check_bytes8(start, value, prefix);
+ if (r)
+ return r;
+ start += prefix;
+ bytes -= prefix;
+ }
+
+ words = bytes / 8;
+
+ while (words) {
+ if (*(u64 *)start != value64)
+ return check_bytes8(start, value, 8);
+ start += 8;
+ words--;
+ }
+
+ return check_bytes8(start, value, bytes % 8);
+}
--
2.26.2