text: #include <stdio.h>
  #include <stdlib.h>
  #include <string.h>
  #include <langinfo.h>
  #include <locale.h>
  #include <time.h>
  #include <limits.h>
  #include "locale_impl.h"
  #include "libc.h"
  #include "time_impl.h"
  
  const char *__nl_langinfo_l(nl_item, locale_t);
  
  static int is_leap(int y)
  {
  	/* Avoid overflow */
  	if (y>INT_MAX-1900) y -= 2000;
  	y += 1900;
  	return !(y%4) && ((y%100) || !(y%400));
  }
  
  static int week_num(const struct tm *tm)
  {
  	int val = (tm->tm_yday + 7U - (tm->tm_wday+6U)%7) / 7;
  	/* If 1 Jan is just 1-3 days past Monday,
  	 * the previous week is also in this year. */
  	if ((tm->tm_wday + 371U - tm->tm_yday - 2) % 7 <= 2)
  		val++;
  	if (!val) {
  		val = 52;
  		/* If 31 December of prev year a Thursday,
  		 * or Friday of a leap year, then the
  		 * prev year has 53 weeks. */
  		int dec31 = (tm->tm_wday + 7U - tm->tm_yday - 1) % 7;
  		if (dec31 == 4 || (dec31 == 5 && is_leap(tm->tm_year%400-1)))
  			val++;
  	} else if (val == 53) {
  		/* If 1 January is not a Thursday, and not
  		 * a Wednesday of a leap year, then this
  		 * year has only 52 weeks. */
  		int jan1 = (tm->tm_wday + 371U - tm->tm_yday) % 7;
  		if (jan1 != 4 && (jan1 != 3 || !is_leap(tm->tm_year)))
  			val = 1;
  	}
  	return val;
  }
  
  const char *__tm_to_tzname(const struct tm *);
  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, int pad)
  {
  	nl_item item;
  	long long val;
  	const char *fmt = "-";
  	int width = 2, def_pad = '0';
  
  	switch (f) {
  	case 'a':
  		if (tm->tm_wday > 6U) goto string;
  		item = ABDAY_1 + tm->tm_wday;
  		goto nl_strcat;
  	case 'A':
  		if (tm->tm_wday > 6U) goto string;
  		item = DAY_1 + tm->tm_wday;
  		goto nl_strcat;
  	case 'h':
  	case 'b':
  		if (tm->tm_mon > 11U) goto string;
  		item = ABMON_1 + tm->tm_mon;
  		goto nl_strcat;
  	case 'B':
  		if (tm->tm_mon > 11U) goto string;
  		item = MON_1 + tm->tm_mon;
  		goto nl_strcat;
  	case 'c':
  		item = D_T_FMT;
  		goto nl_strftime;
  	case 'C':
  		val = (1900LL+tm->tm_year) / 100;
  		goto number;
  	case 'e':
  		def_pad = '_';
  	case 'd':
  		val = tm->tm_mday;
  		goto number;
  	case 'D':
  		fmt = "%m/%d/%y";
  		goto recu_strftime;
  	case 'F':
  		fmt = "%Y-%m-%d";
  		goto recu_strftime;
  	case 'g':
  	case 'G':
  		val = tm->tm_year + 1900LL;
  		if (tm->tm_yday < 3 && week_num(tm) != 1) val--;
  		else if (tm->tm_yday > 360 && week_num(tm) == 1) val++;
  		if (f=='g') val %= 100;
  		else width = 4;
  		goto number;
  	case 'H':
  		val = tm->tm_hour;
  		goto number;
  	case 'I':
  		val = tm->tm_hour;
  		if (!val) val = 12;
  		else if (val > 12) val -= 12;
  		goto number;
  	case 'j':
  		val = tm->tm_yday+1;
  		width = 3;
  		goto number;
  	case 'm':
  		val = tm->tm_mon+1;
  		goto number;
  	case 'M':
  		val = tm->tm_min;
  		goto number;
  	case 'n':
  		*l = 1;
  		return "\n";
  	case 'p':
  		item = tm->tm_hour >= 12 ? PM_STR : AM_STR;
  		goto nl_strcat;
  	case 'r':
  		item = T_FMT_AMPM;
  		goto nl_strftime;
  	case 'R':
  		fmt = "%H:%M";
  		goto recu_strftime;
  	case 's':
  		val = __tm_to_secs(tm) - tm->__tm_gmtoff;
  		width = 1;
  		goto number;
  	case 'S':
  		val = tm->tm_sec;
  		goto number;
  	case 't':
  		*l = 1;
  		return "\t";
  	case 'T':
  		fmt = "%H:%M:%S";
  		goto recu_strftime;
  	case 'u':
  		val = tm->tm_wday ? tm->tm_wday : 7;
  		width = 1;
  		goto number;
  	case 'U':
  		val = (tm->tm_yday + 7U - tm->tm_wday) / 7;
  		goto number;
  	case 'W':
  		val = (tm->tm_yday + 7U - (tm->tm_wday+6U)%7) / 7;
  		goto number;
  	case 'V':
  		val = week_num(tm);
  		goto number;
  	case 'w':
  		val = tm->tm_wday;
  		width = 1;
  		goto number;
  	case 'x':
  		item = D_FMT;
  		goto nl_strftime;
  	case 'X':
  		item = T_FMT;
  		goto nl_strftime;
  	case 'y':
  		val = (tm->tm_year + 1900LL) % 100;
  		if (val < 0) val = -val;
  		goto number;
  	case 'Y':
  		val = tm->tm_year + 1900LL;
  		if (val >= 10000) {
  			*l = snprintf(*s, sizeof *s, "+%lld", val);
  			return *s;
  		}
  		width = 4;
  		goto number;
  	case 'z':
  		if (tm->tm_isdst < 0) {
  			*l = 0;
  			return "";
  		}
  		*l = snprintf(*s, sizeof *s, "%+.2d%.2d",
  			(tm->__tm_gmtoff)/3600,
  			abs(tm->__tm_gmtoff%3600)/60);
  		return *s;
  	case 'Z':
  		if (tm->tm_isdst < 0) {
  			*l = 0;
  			return "";
  		}
  		fmt = __tm_to_tzname(tm);
  		goto string;
  	case '%':
  		*l = 1;
  		return "%";
  	default:
  		return 0;
  	}
  number:
  	switch (pad ? pad : def_pad) {
  	case '-': *l = snprintf(*s, sizeof *s, "%lld", val); break;
  	case '_': *l = snprintf(*s, sizeof *s, "%*lld", width, val); break;
  	case '0':
  	default:  *l = snprintf(*s, sizeof *s, "%0*lld", width, val); break;
  	}
  	return *s;
  nl_strcat:
  	fmt = __nl_langinfo_l(item, loc);
  string:
  	*l = strlen(fmt);
  	return fmt;
  nl_strftime:
  	fmt = __nl_langinfo_l(item, loc);
  recu_strftime:
  	*l = __strftime_l(*s, sizeof *s, fmt, tm, loc);
  	if (!*l) return 0;
  	return *s;
  }
  
  size_t __strftime_l(char *restrict s, size_t n, const char *restrict f, const struct tm *restrict tm, locale_t loc)
  {
  	size_t l, k;
  	char buf[100];
  	char *p;
  	const char *t;
  	int pad, plus;
  	unsigned long width;
  	for (l=0; l<n; f++) {
  		if (!*f) {
  			s[l] = 0;
  			return l;
  		}
  		if (*f != '%') {
  			s[l++] = *f;
  			continue;
  		}
  		f++;
  		pad = 0;
  		if (*f == '-' || *f == '_' || *f == '0') pad = *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;
  		} else {
  			width = 0;
  		}
  		f = p;
  		if (*f == 'E' || *f == 'O') f++;
  		t = __strftime_fmt_1(&buf, &k, *f, tm, loc, pad);
  		if (!t) break;
  		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++;
  			for (; width > k && l < n; width--)
  				s[l++] = '0';
  		}
  		if (k > n-l) k = n-l;
  		memcpy(s+l, t, k);
  		l += k;
  	}
  	if (n) {
  		if (l==n) l=n-1;
  		s[l] = 0;
  	}
  	return 0;
  }
  
  size_t strftime(char *restrict s, size_t n, const char *restrict f, const struct tm *restrict tm)
  {
  	return __strftime_l(s, n, f, tm, CURRENT_LOCALE);
  }
  
  weak_alias(__strftime_l, strftime_l);
  