fix unhandled cases in strptime

%C, %U, %W, and %y handling were completely missing; %C wrongly
fell-through to unrelated cases, and the rest returned failure. for
now, they all parse numbers in the proper forms and range-check the
values, but they do not store the value anywhere.

it's not clear to me whether, as "derived" fields, %U and %W should
produce any result. they certainly cannot produce a result unless the
year and weekday are also converted, but in this case it might be
desirable for them to do so. clarification is needed on the intended
behavior of strptime in cases like this.

%C and %y have well-defined behavior as long as they are used together
(and %y is defined by itself but may change in the future).
implementing them (including their correct interaction) is left as a
later change to be made.

finally, strptime now rejects unknown/invalid format characters
instead of ignoring them.

src/time/strptime.c

@@ -8,7 +8,7 @@
 
 char *strptime(const char *restrict s, const char *restrict f, struct tm *restrict tm)
 {
-	int i, w, neg, adj, min, range, *dest;
+	int i, w, neg, adj, min, range, *dest, dummy;
 	const char *ex;
 	size_t len;
 	while (*f) {
@@ -40,6 +40,10 @@ char *strptime(const char *restrict s, const char *restrict f, struct tm *restri
 			if (!s) return 0;
 			break;
 		case 'C':
+			/* FIXME */
+			dest = &dummy;
+			if (w<0) w=2;
+			goto numeric_digits;
 		case 'd': case 'e':
 			dest = &tm->tm_mday;
 			min = 1;
@@ -112,8 +116,11 @@ char *strptime(const char *restrict s, const char *restrict f, struct tm *restri
 			break;
 		case 'U':
 		case 'W':
-			//FIXME
-			return 0;
+			/* Throw away result, for now. (FIXME?) */
+			dest = &dummy;
+			min = 0;
+			range = 54;
+			goto numeric_range;
 		case 'w':
 			dest = &tm->tm_wday;
 			min = 0;
@@ -128,8 +135,10 @@ char *strptime(const char *restrict s, const char *restrict f, struct tm *restri
 			if (!s) return 0;
 			break;
 		case 'y':
-			//FIXME
-			return 0;
+			/* FIXME */
+			dest = &dummy;
+			w = 2;
+			goto numeric_digits;
 		case 'Y':
 			dest = &tm->tm_year;
 			if (w<0) w=4;
@@ -138,6 +147,8 @@ char *strptime(const char *restrict s, const char *restrict f, struct tm *restri
 		case '%':
 			if (*s++ != '%') return 0;
 			break;
+		default:
+			return 0;
 		numeric_range:
 			if (!isdigit(*s)) return 0;
 			*dest = 0;