implement strnlen for systems that need it

Prior the Mac OS 10.7, the function strnlen() was not available. This patch
implements strnlen() on Mac OS X versions that are below 10.7.

Signed-off-by: John Arbuckle <programmingkidx@gmail.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

libfdt/libfdt_env.h

@@ -109,4 +109,31 @@ static inline fdt64_t cpu_to_fdt64(uint64_t x)
 #undef CPU_TO_FDT16
 #undef EXTRACT_BYTE
 
+#ifdef __APPLE__
+#include <AvailabilityMacros.h>
+
+/* strnlen() is not available on Mac OS < 10.7 */
+# if !defined(MAC_OS_X_VERSION_10_7) || (MAC_OS_X_VERSION_MAX_ALLOWED < \
+                                         MAC_OS_X_VERSION_10_7)
+
+#define strnlen fdt_strnlen
+
+/*
+ * fdt_strnlen: returns the length of a string or max_count - which ever is
+ * smallest.
+ * Input 1 string: the string whose size is to be determined
+ * Input 2 max_count: the maximum value returned by this function
+ * Output: length of the string or max_count (the smallest of the two)
+ */
+static inline size_t fdt_strnlen(const char *string, size_t max_count)
+{
+    const char *p = memchr(string, 0, max_count);
+    return p ? p - string : max_count;
+}
+
+#endif /* !defined(MAC_OS_X_VERSION_10_7) || (MAC_OS_X_VERSION_MAX_ALLOWED <
+          MAC_OS_X_VERSION_10_7) */
+
+#endif /* __APPLE__ */
+
 #endif /* LIBFDT_ENV_H */