add strftime and wcsftime field widths

at present, since POSIX requires %F to behave as %+4Y-%m-%d and ISO C
requires %F to behave as %Y-%m-%d, the default behavior for %Y has
been changed to match %+4Y. this seems to be the only way to conform
to the requirements of both standards, and it does not affect years
prior to the year 10000. depending on the outcome of interpretations
from the standards bodies, this may be adjusted at some point.

src/time/strftime.c

@@ -157,7 +157,11 @@ const char *__strftime_fmt_1(char (*s)[100], size_t *l, int f, const struct tm *
 		val = tm->tm_year % 100;
 		goto number;
 	case 'Y':
-		val = tm->tm_year + 1900LL;
+		val = tm->tm_year + 1900;
+		if (val >= 10000) {
+			*l = snprintf(*s, sizeof *s, "+%lld", val);
+			return *s;
+		}
 		width = 4;
 		goto number;
 	case 'z':
@@ -193,7 +197,10 @@ size_t __strftime_l(char *restrict s, size_t n, const char *restrict f, const st
 {
 	size_t l, k;
 	char buf[100];
+	char *p;
 	const char *t;
+	int plus;
+	unsigned long width;
 	for (l=0; l+1<n; f++) {
 		if (!*f) {
 			s[l] = 0;
@@ -204,10 +211,32 @@ size_t __strftime_l(char *restrict s, size_t n, const char *restrict f, const st
 			continue;
 		}
 		f++;
+		if ((plus = (*f == '+'))) f++;
+		width = strtoul(f, &p, 10);
+		if (*p == 'C' || *p == 'F' || *p == 'G' || *p == 'Y') {
+			if (!width && p!=f) width = 1;
+			if (width >= n-l) return 0;
+		} else {
+			width = 0;
+		}
+		f = p;
 		if (*f == 'E' || *f == 'O') f++;
 		t = __strftime_fmt_1(&buf, &k, *f, tm, loc);
-		if (!t || k >= n-l)
-			return 0;
+		if (!t) return 0;
+		if (width) {
+			for (; *t=='+' || *t=='-' || (*t=='0'&&t[1]); t++, k--);
+			width--;
+			if (plus && tm->tm_year >= 10000-1900)
+				s[l++] = '+';
+			else if (tm->tm_year < -1900)
+				s[l++] = '-';
+			else
+				width++;
+			if (width >= n-l) return 0;
+			for (; width > k; width--)
+				s[l++] = '0';
+		}
+		if (k >= n-l) return 0;
 		memcpy(s+l, t, k);
 		l += k;
 	}

src/time/wcsftime.c

@@ -4,33 +4,61 @@
 #include <locale.h>
 #include "libc.h"
 
-size_t __strftime_l(char *restrict, size_t, const char *restrict, const struct tm *restrict, locale_t);
+const char *__strftime_fmt_1(char (*s)[100], size_t *l, int f, const struct tm *tm, locale_t loc);
 
-size_t __wcsftime_l(wchar_t *restrict wcs, size_t n, const wchar_t *restrict f, const struct tm *restrict tm, locale_t loc)
+size_t __wcsftime_l(wchar_t *restrict s, size_t n, const wchar_t *restrict f, const struct tm *restrict tm, locale_t loc)
 {
-	size_t k, n0=n;
-	char out[100], in[4];
-	while (*f) {
-		if (!n) return 0;
+	size_t l, k;
+	char buf[100];
+	wchar_t wbuf[100];
+	wchar_t *p;
+	const char *t_mb;
+	const wchar_t *t;
+	int plus;
+	unsigned long width;
+	for (l=0; l+1<n; f++) {
+		if (!*f) {
+			s[l] = 0;
+			return l;
+		}
 		if (*f != '%') {
-			*wcs++ = *f++;
-			n--;
+			s[l++] = *f;
 			continue;
 		}
-		in[2] = in[3] = 0;
-		in[0] = *f++;
-		if (strchr("EO", (in[1]=*f++)))
-			in[2] = *f++;
-		k = __strftime_l(out, sizeof out, in, tm, loc);
-		if (!k) return 0;
-		k = mbsrtowcs(wcs, (const char *[]){out}, n, 0);
-		if (k==(size_t)-1) return 0;
-		wcs += k;
-		n -= k;
+		f++;
+		if ((plus = (*f == '+'))) f++;
+		width = wcstoul(f, &p, 10);
+		if (*p == 'C' || *p == 'F' || *p == 'G' || *p == 'Y') {
+			if (!width && p!=f) width = 1;
+			if (width >= n-l) return 0;
+		} else {
+			width = 0;
+		}
+		f = p;
+		if (*f == 'E' || *f == 'O') f++;
+		t_mb = __strftime_fmt_1(&buf, &k, *f, tm, loc);
+		if (!t_mb) return 0;
+		k = mbstowcs(wbuf, t_mb, sizeof wbuf / sizeof *wbuf);
+		if (k == (size_t)-1) return 0;
+		t = wbuf;
+		if (width) {
+			for (; *t=='+' || *t=='-' || (*t=='0'&&t[1]); t++, k--);
+			width--;
+			if (plus && tm->tm_year >= 10000-1900)
+				s[l++] = '+';
+			else if (tm->tm_year < -1900)
+				s[l++] = '-';
+			else
+				width++;
+			if (width >= n-l) return 0;
+			for (; width > k; width--)
+				s[l++] = '0';
+		}
+		if (k >= n-l) return 0;
+		wmemcpy(s+l, t, k);
+		l += k;
 	}
-	if (!n) return 0;
-	*wcs++ = 0;
-	return n0-n;
+	return 0;
 }
 
 size_t wcsftime(wchar_t *restrict wcs, size_t n, const wchar_t *restrict f, const struct tm *restrict tm)