libc: revert date change again. this is getting ridicuoulus.

this breaks the sample from the seconds manpage, and overall
produces funky results. this needs alot more testing.

term% seconds '23 may 2011'
seconds: tmparse: invalid date 23 may 2011 near 'may 2011'

term% seconds '2019-01-01 00:00:00'
-118370073600

1 files changed, 195 insertions, 2 deletions

diff --git a/sys/src/libc/9sys/tm2sec.c b/sys/src/libc/9sys/tm2sec.c
index 96d4c3d61..20bebd0c8 100644
--- a/sys/src/libc/9sys/tm2sec.c
+++ b/sys/src/libc/9sys/tm2sec.c
@@ -1,9 +1,202 @@
 #include <u.h>
 #include <libc.h>
 
+#define	TZSIZE	150
+static	void	readtimezone(void);
+static	int	rd_name(char**, char*);
+static	int	rd_long(char**, long*);
+static
+struct
+{
+	char	stname[4];
+	char	dlname[4];
+	long	stdiff;
+	long	dldiff;
+	long	dlpairs[TZSIZE];
+} timezone;
+
+#define SEC2MIN 60L
+#define SEC2HOUR (60L*SEC2MIN)
+#define SEC2DAY (24L*SEC2HOUR)
+
+/*
+ *  days per month plus days/year
+ */
+static	int	dmsize[] =
+{
+	365, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31
+};
+static	int	ldmsize[] =
+{
+	366, 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31
+};
+
+/*
+ *  return the days/month for the given year
+ */
+static int *
+yrsize(int y)
+{
+	if((y%4) == 0 && ((y%100) != 0 || (y%400) == 0))
+		return ldmsize;
+	else
+		return dmsize;
+}
+
+/*
+ * compute seconds since Jan 1 1970 GMT
+ * and convert to our timezone.
+ */
 long
 tm2sec(Tm *tm)
 {
-	tmnorm(tm);
-	return tm->abs;
+	long secs, *p;
+	int i, yday, year, *d2m;
+
+	if(strcmp(tm->zone, "GMT") != 0 && timezone.stname[0] == 0)
+		readtimezone();
+	secs = 0;
+
+	/*
+	 *  seconds per year
+	 */
+	year = tm->year + 1900;
+	for(i = 1970; i < year; i++){
+		d2m = yrsize(i);
+		secs += d2m[0] * SEC2DAY;
+	}
+
+	/*
+	 *  if mday is set, use mon and mday to compute yday
+	 */
+	if(tm->mday){
+		yday = 0;
+		d2m = yrsize(year);
+		for(i=0; i<tm->mon; i++)
+			yday += d2m[i+1];
+		yday += tm->mday-1;
+	}else{
+		yday = tm->yday;
+	}
+	secs += yday * SEC2DAY;
+
+	/*
+	 * hours, minutes, seconds
+	 */
+	secs += tm->hour * SEC2HOUR;
+	secs += tm->min * SEC2MIN;
+	secs += tm->sec;
+
+	/*
+	 * Only handles zones mentioned in /env/timezone,
+	 * but things get too ambiguous otherwise.
+	 */
+	if(strcmp(tm->zone, timezone.stname) == 0)
+		secs -= timezone.stdiff;
+	else if(strcmp(tm->zone, timezone.dlname) == 0)
+		secs -= timezone.dldiff;
+	else if(tm->zone[0] == 0){
+		secs -= timezone.dldiff;
+		for(p = timezone.dlpairs; *p; p += 2)
+			if(secs >= p[0] && secs < p[1])
+				break;
+		if(*p == 0){
+			secs += timezone.dldiff;
+			secs -= timezone.stdiff;
+		}
+	}
+	return secs;
+}
+
+static
+void
+readtimezone(void)
+{
+	char buf[TZSIZE*11+30], *p;
+	int i;
+
+	memset(buf, 0, sizeof(buf));
+	i = open("/env/timezone", 0);
+	if(i < 0)
+		goto error;
+	if(read(i, buf, sizeof(buf)) >= sizeof(buf))
+		goto error;
+	close(i);
+	p = buf;
+	if(rd_name(&p, timezone.stname))
+		goto error;
+	if(rd_long(&p, &timezone.stdiff))
+		goto error;
+	if(rd_name(&p, timezone.dlname))
+		goto error;
+	if(rd_long(&p, &timezone.dldiff))
+		goto error;
+	for(i=0; i<TZSIZE; i++) {
+		if(rd_long(&p, &timezone.dlpairs[i]))
+			goto error;
+		if(timezone.dlpairs[i] == 0)
+			return;
+	}
+
+error:
+	timezone.stdiff = 0;
+	strcpy(timezone.stname, "GMT");
+	timezone.dlpairs[0] = 0;
+}
+
+static int
+rd_name(char **f, char *p)
+{
+	int c, i;
+
+	for(;;) {
+		c = *(*f)++;
+		if(c != ' ' && c != '\n')
+			break;
+	}
+	for(i=0; i<3; i++) {
+		if(c == ' ' || c == '\n')
+			return 1;
+		*p++ = c;
+		c = *(*f)++;
+	}
+	if(c != ' ' && c != '\n')
+		return 1;
+	*p = 0;
+	return 0;
+}
+
+static int
+rd_long(char **f, long *p)
+{
+	int c, s;
+	long l;
+
+	s = 0;
+	for(;;) {
+		c = *(*f)++;
+		if(c == '-') {
+			s++;
+			continue;
+		}
+		if(c != ' ' && c != '\n')
+			break;
+	}
+	if(c == 0) {
+		*p = 0;
+		return 0;
+	}
+	l = 0;
+	for(;;) {
+		if(c == ' ' || c == '\n')
+			break;
+		if(c < '0' || c > '9')
+			return 1;
+		l = l*10 + c-'0';
+		c = *(*f)++;
+	}
+	if(s)
+		l = -l;
+	*p = l;
+	return 0;
 }