Clean up overly paranoid checks in mac8.c

Andres' compiler points out, quite correctly, that there's no need for
some of the overly paranoid checks which were put into mac8.c.  Remove
those, as they're useless, add some comments and make a few other minor
improvements- reduce the size of hexlookup by making it a char array
instead of an int array, and pass in the ptr location directly instead
of making hex2_to_uchar re-calculate the location based off the offset
every time.

src/backend/utils/adt/mac8.c

@@ -35,9 +35,9 @@
 #define lobits(addr) \
   ((unsigned long)(((addr)->e<<24) | ((addr)->f<<16) | ((addr)->g<<8) | ((addr)->h)))
 
-static unsigned char hex2_to_uchar(const char *str, int offset);
+static unsigned char hex2_to_uchar(const char *str, const char *ptr);
 
-static const int hexlookup[128] = {
+static const char hexlookup[128] = {
 	-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
 	-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
 	-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
@@ -48,19 +48,27 @@ static const int hexlookup[128] = {
 	-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
 };
 
+/*
+ * hex2_to_uchar - convert 2 hex digits to a byte (unsigned char)
+ *
+ * This will ereport() if the end of the string is reached ('\0' found), or if
+ * either character is not a valid hex digit.
+ *
+ * ptr is the pointer to where the digits to convert are in the string, str is
+ * the entire string, which is used only for error reporting.
+ */
 static inline unsigned char
-hex2_to_uchar(const char *str, int offset)
+hex2_to_uchar(const char *ptr, const char *str)
 {
 	unsigned char ret = 0;
-	int			lookup;
-	const char *ptr = str + offset;
+	char		lookup;
 
 	/* Handle the first character */
-	if (*ptr < 0 || *ptr >= 127)
+	if (*ptr < 0)
 		goto invalid_input;
 
 	lookup = hexlookup[(unsigned char) *ptr];
-	if (lookup < 0 || lookup > 15)
+	if (lookup < 0)
 		goto invalid_input;
 
 	ret = lookup << 4;
@@ -68,11 +76,11 @@ hex2_to_uchar(const char *str, int offset)
 	/* Move to the second character */
 	ptr++;
 
-	if (*ptr < 0 || *ptr > 127)
+	if (*ptr < 0)
 		goto invalid_input;
 
 	lookup = hexlookup[(unsigned char) *ptr];
-	if (lookup < 0 || lookup > 15)
+	if (lookup < 0)
 		goto invalid_input;
 
 	ret += lookup;
@@ -128,28 +136,28 @@ macaddr8_in(PG_FUNCTION_ARGS)
 		switch (count)
 		{
 			case 1:
-				a = hex2_to_uchar(str, ptr - str);
+				a = hex2_to_uchar(ptr, str);
 				break;
 			case 2:
-				b = hex2_to_uchar(str, ptr - str);
+				b = hex2_to_uchar(ptr, str);
 				break;
 			case 3:
-				c = hex2_to_uchar(str, ptr - str);
+				c = hex2_to_uchar(ptr, str);
 				break;
 			case 4:
-				d = hex2_to_uchar(str, ptr - str);
+				d = hex2_to_uchar(ptr, str);
 				break;
 			case 5:
-				e = hex2_to_uchar(str, ptr - str);
+				e = hex2_to_uchar(ptr, str);
 				break;
 			case 6:
-				f = hex2_to_uchar(str, ptr - str);
+				f = hex2_to_uchar(ptr, str);
 				break;
 			case 7:
-				g = hex2_to_uchar(str, ptr - str);
+				g = hex2_to_uchar(ptr, str);
 				break;
 			case 8:
-				h = hex2_to_uchar(str, ptr - str);
+				h = hex2_to_uchar(ptr, str);
 				break;
 			default:
 				/* must be trailing garbage... */