On Fri, 30 Apr 2010 12:34:00 +0300
Andy Shevchenko <ext-andriy.shevchenko@nokia.com> wrote:

>  /**
> + * 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 >= 'a') && (ch <= 'f'))
> +		return ch - 'a' + 10;
> +	if ((ch >= '0') && (ch <= '9'))
> +		return ch - '0';
> +	if ((ch >= 'A') && (ch <= 'F'))
> +		return ch - 'A' + 10;
> +	return -1;
> +}
> +EXPORT_SYMBOL(hex_to_bin);

I had to fiddle with it:

- use tolower(), saving 3 bytes!

- test the more common case first - it's quicker.

diff -puN lib/hexdump.c~lib-introduce-common-method-to-convert-hex-digits-fix lib/hexdump.c
--- a/lib/hexdump.c~lib-introduce-common-method-to-convert-hex-digits-fix
+++ a/lib/hexdump.c
@@ -24,12 +24,11 @@ EXPORT_SYMBOL(hex_asc);
  */
 int hex_to_bin(char ch)
 {
-	if ((ch >= 'a') && (ch <= 'f'))
-		return ch - 'a' + 10;
+	ch = tolower(ch);
 	if ((ch >= '0') && (ch <= '9'))
 		return ch - '0';
-	if ((ch >= 'A') && (ch <= 'F'))
-		return ch - 'A' + 10;
+	if ((ch >= 'a') && (ch <= 'f'))
+		return ch - 'a' + 10;
 	return -1;
 }
 EXPORT_SYMBOL(hex_to_bin);
_

Yielding

int hex_to_bin(char ch)
{
	ch = tolower(ch);
	if ((ch >= '0') && (ch <= '9'))
		return ch - '0';
	if ((ch >= 'a') && (ch <= 'f'))
		return ch - 'a' + 10;
	return -1;
}