lib: introduce common method to convert hex digits

hex_to_bin() is a little method which converts hex digit to its actual
value.  There are plenty of places where such functionality is needed.

[akpm@linux-foundation.org: use tolower(), saving 3 bytes, test the more common case first - it's quicker]
[akpm@linux-foundation.org: relocate tolower to make it even faster! (Joe)]
Signed-off-by: Andy Shevchenko <ext-andriy.shevchenko@nokia.com>
Cc: Tilman Schmidt <tilman@imap.cc>
Cc: Duncan Sands <duncan.sands@free.fr>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Greg Kroah-Hartman <gregkh@suse.de>
Cc: "Richard Russon (FlatCap)" <ldm@flatcap.org>
Cc: John W. Linville <linville@tuxdriver.com>
Cc: Len Brown <lenb@kernel.org>
Cc: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 20 insertions, 0 deletions

diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 05f332afc9e0..8317ec4b9f3b 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -375,6 +375,8 @@ static inline char *pack_hex_byte(char *buf, u8 byte)
         return buf;
 }
 
+extern int hex_to_bin(char ch);
+
 #ifndef pr_fmt
 #define pr_fmt(fmt) fmt
 #endif
diff --git a/lib/hexdump.c b/lib/hexdump.c
index 1bd6a9779774..5d7a4802c562 100644
--- a/lib/hexdump.c
+++ b/lib/hexdump.c
@@ -16,6 +16,24 @@ const char hex_asc[] = "0123456789abcdef";
 EXPORT_SYMBOL(hex_asc);
 
 /**
+ * hex_to_bin - convert a hex digit to its real value
+ * @ch: ascii character represents hex digit
+ *
+ * hex_to_bin() converts one hex digit to its actual value or -1 in case of bad
+ * input.
+ */
+int hex_to_bin(char ch)
+{
+        if ((ch >= '0') && (ch <= '9'))
+                return ch - '0';
+        ch = tolower(ch);
+        if ((ch >= 'a') && (ch <= 'f'))
+                return ch - 'a' + 10;
+        return -1;
+}
+EXPORT_SYMBOL(hex_to_bin);
+
+/**
  * hex_dump_to_buffer - convert a blob of data to "hex ASCII" in memory
  * @buf: data blob to dump
  * @len: number of bytes in the @buf