lib: add ascii hex helper functions

index 4d46e29..20cae9a 100644
@@ -276,7 +276,11 @@ extern void print_hex_dump(const char *level, const char *prefix_str,
 				const void *buf, size_t len, bool ascii);
 extern void print_hex_dump_bytes(const char *prefix_str, int prefix_type,
 			const void *buf, size_t len);
-#define hex_asc(x)	"0123456789abcdef"[x]
+
+extern const char hex_asc[];
+extern int hex_to_int(char c);
+#define hex_asc_lo(x)	hex_asc[((x) & 0x0f)]
+#define hex_asc_hi(x)	hex_asc[((x) & 0xf0) >> 4]
 
 #define pr_emerg(fmt, arg...) \
 	printk(KERN_EMERG fmt, ##arg)

index 3435465..fa1a76e 100644
@@ -12,6 +12,27 @@
 #include <linux/kernel.h>
 #include <linux/module.h>
 
+const char hex_asc[] = "0123456789abcdef";
+
+/**
+ * hex_to_int - convert a single hex ASCII char to an integer value
+ * @ch: char to convert, not case sensitive [a-f][A-F][0-9]
+ *
+ * Returns -1 if the char is not a valid hexadecimal character
+ */
+int hex_to_int(char ch)
+{
+	/*
+	 * Make ch lower-case, works only for digits and letters
+	 */
+	ch |= 0x20;
+	if (ch >= 'a' && ch <= 'f')
+		return ch - 'a' + 10;
+	if (ch >= '0' && ch <= '9')
+		return ch - '0';
+	return -1;
+}
+
 /**
  * hex_dump_to_buffer - convert a blob of data to "hex ASCII" in memory
  * @buf: data blob to dump

@@ -93,8 +114,8 @@ void hex_dump_to_buffer(const void *buf, size_t len, int rowsize,
 		for (j = 0; (j < rowsize) && (j < len) && (lx + 4) < linebuflen;
 		     j++) {
 			ch = ptr[j];
-			linebuf[lx++] = hex_asc(ch >> 4);
-			linebuf[lx++] = hex_asc(ch & 0x0f);
+			linebuf[lx++] = hex_asc_hi(ch);
+			linebuf[lx++] = hex_asc_lo(ch);
 			linebuf[lx++] = ' ';
 		}
 		ascii_column = 3 * rowsize + 2;

index 3eba85e..95b076c 100644
@@ -45,10 +45,10 @@ void pnp_eisa_id_to_string(u32 id, char *str)
 	str[0] = 'A' + ((id >> 26) & 0x3f) - 1;
 	str[1] = 'A' + ((id >> 21) & 0x1f) - 1;
 	str[2] = 'A' + ((id >> 16) & 0x1f) - 1;
-	str[3] = hex_asc((id >> 12) & 0xf);
-	str[4] = hex_asc((id >>  8) & 0xf);
-	str[5] = hex_asc((id >>  4) & 0xf);
-	str[6] = hex_asc((id >>  0) & 0xf);
+	str[3] = hex_asc_hi(id >> 8);
+	str[4] = hex_asc_lo(id >> 8);
+	str[5] = hex_asc_hi(id);
+	str[6] = hex_asc_lo(id);
 	str[7] = '\0';
 }