lib: use proper unsigned type for walking string

Use a pointer to unsigned char as the type of variable to walk the
string and write the output. Important since we know that character
values can be over 127, and we use the value as an index into a 256-part
array during decoding. After this change, we can also remove some ugly
typecasts.

lib/dec/head.c

@@ -1,6 +1,6 @@
 int ret = 0;
-const char *c = src;
-char *o = out;
+const unsigned char *c = (const unsigned char *)src;
+unsigned char *o = (unsigned char *)out;
 unsigned char q;
 
 /* Use local temporaries to avoid cache thrashing: */

lib/dec/tail.c

@@ -2,7 +2,7 @@
 			ret = 1;
 			break;
 		}
-		if ((q = base64_table_dec[(unsigned char)*c++]) >= 254) {
+		if ((q = base64_table_dec[*c++]) >= 254) {
 			st.eof = 1;
 			/* Treat character '=' as invalid for byte 0: */
 			break;
@@ -14,7 +14,7 @@
 			ret = 1;
 			break;
 		}
-		if ((q = base64_table_dec[(unsigned char)*c++]) >= 254) {
+		if ((q = base64_table_dec[*c++]) >= 254) {
 			st.eof = 1;
 			/* Treat character '=' as invalid for byte 1: */
 			break;
@@ -28,7 +28,7 @@
 			ret = 1;
 			break;
 		}
-		if ((q = base64_table_dec[(unsigned char)*c++]) >= 254) {
+		if ((q = base64_table_dec[*c++]) >= 254) {
 			st.eof = 1;
 			/* When q == 254, the input char is '='. Return 1 and EOF.
 			 * Technically, should check if next byte is also '=', but never mind.
@@ -45,7 +45,7 @@
 			ret = 1;
 			break;
 		}
-		if ((q = base64_table_dec[(unsigned char)*c++]) >= 254) {
+		if ((q = base64_table_dec[*c++]) >= 254) {
 			st.eof = 1;
 			/* When q == 254, the input char is '='. Return 1 and EOF.
 			 * When q == 255, the input char is invalid. Return 0 and EOF. */

lib/enc/head.c

@@ -1,7 +1,7 @@
 /* Assume that *out is large enough to contain the output.
  * Theoretically it should be 4/3 the length of src. */
-const unsigned char *c = (unsigned char *)src;
-char *o = out;
+const unsigned char *c = (const unsigned char *)src;
+unsigned char *o = (unsigned char *)out;
 
 /* Use local temporaries to avoid cache thrashing: */
 size_t outl = 0;