Optimize to_binstr() function

Appending multiple times to same string is slow since strcat() needs
to determine the end during each run. So manually maintain a pointer
to the end to speed-up things.

Signed-off-by: Michael Heimpold <michael.heimpold@i2se.com>
Cc: Michael Heimpold <mhei@heimpold.de>
Reviewed-by: Avri Altman <avri.altman@wdc.com>
Signed-off-by: Chris Ball <chris@printf.net>

lsmmc.c

@@ -371,12 +371,14 @@ char *to_binstr(char *hexstr)
 		"0000", "0001", "0010", "0011", "0100", "0101", "0110", "0111",
 		"1000", "1001", "1010", "1011", "1100", "1101", "1110", "1111",
 	};
-	char *binstr;
+	char *binstr, *tail;
 
 	binstr = calloc(strlen(hexstr) * 4 + 1, sizeof(char));
 	if (!binstr)
 		return NULL;
 
+	tail = binstr;
+
 	while (hexstr && *hexstr != '\0') {
 		if (!isxdigit(*hexstr)) {
 			free(binstr);
@@ -384,13 +386,14 @@ char *to_binstr(char *hexstr)
 		}
 
 		if (isdigit(*hexstr))
-			strcat(binstr, bindigits[*hexstr - '0']);
+			strcat(tail, bindigits[*hexstr - '0']);
 		else if (islower(*hexstr))
-			strcat(binstr, bindigits[*hexstr - 'a' + 10]);
+			strcat(tail, bindigits[*hexstr - 'a' + 10]);
 		else
-			strcat(binstr, bindigits[*hexstr - 'A' + 10]);
+			strcat(tail, bindigits[*hexstr - 'A' + 10]);
 
 		hexstr++;
+		tail += 4;
 	}
 
 	return binstr;