the big time handling overhaul

this commit has two major user-visible parts: zoneinfo-format time
zones are now supported, and overflow handling is intended to be
complete in the sense that all functions return a correct result if
and only if the result fits in the destination type, and otherwise
return an error. also, some noticable bugs in the way DST detection
and normalization worked have been fixed, and performance may be
better than before, but it has not been tested.

1 files changed, 389 insertions, 0 deletions

diff --git a/src/time/__tz.c b/src/time/__tz.c
new file mode 100644
index 00000000..a76a7b48
--- /dev/null
+++ b/src/time/__tz.c
@@ -0,0 +1,389 @@
+#include "time_impl.h"
+#include <stdint.h>
+#include <limits.h>
+#include <stdlib.h>
+#include <string.h>
+#include "libc.h"
+
+long  __timezone = 0;
+int   __daylight = 0;
+char *__tzname[2] = { 0, 0 };
+
+weak_alias(__timezone, timezone);
+weak_alias(__daylight, daylight);
+weak_alias(__tzname, tzname);
+
+static char std_name[TZNAME_MAX+1];
+static char dst_name[TZNAME_MAX+1];
+
+static int dst_off;
+static int r0[5], r1[5];
+
+static const unsigned char *zi, *trans, *index, *types, *abbrevs;
+static size_t map_size;
+
+static char old_tz_buf[32];
+static char *old_tz = old_tz_buf;
+static size_t old_tz_size = sizeof old_tz_buf;
+
+static int lock[2];
+
+static int getint(const char **p)
+{
+	unsigned x;
+	for (x=0; **p-'0'<10U; (*p)++) x = **p-'0' + 10*x;
+	return x;
+}
+
+static int getsigned(const char **p)
+{
+	if (**p == '-') {
+		++*p;
+		return -getint(p);
+	}
+	if (**p == '+') ++*p;
+	return getint(p);
+}
+
+static int getoff(const char **p)
+{
+	int off = 3600*getsigned(p);
+	if (**p == ':') {
+		++*p;
+		off += 60*getint(p);
+		if (**p == ':') {
+			++*p;
+			off += getint(p);
+		}
+	}
+	return off;
+}
+
+static void getrule(const char **p, int rule[5])
+{
+	int r = rule[0] = **p;
+
+	if (r!='M') {
+		if (r=='J') ++*p;
+		else rule[0] = 0;
+		rule[1] = getint(p);
+	} else {
+		++*p; rule[1] = getint(p);
+		++*p; rule[2] = getint(p);
+		++*p; rule[3] = getint(p);
+	}
+
+	if (**p=='/') {
+		++*p;
+		rule[4] = getoff(p);
+	} else {
+		rule[4] = 7200;
+	}
+}
+
+static void getname(char *d, const char **p)
+{
+	int i;
+	if (**p == '<') {
+		++*p;
+		for (i=0; **p!='>' && i<TZNAME_MAX; i++)
+			d[i] = (*p)[i];
+		++*p;
+	} else {
+		for (i=0; ((*p)[i]|32)-'a'<26U && i<TZNAME_MAX; i++)
+			d[i] = (*p)[i];
+	}
+	*p += i;
+	d[i] = 0;
+}
+
+#define VEC(...) ((const unsigned char[]){__VA_ARGS__})
+
+static uint32_t zi_read32(const unsigned char *z)
+{
+	return (unsigned)z[0]<<24 | z[1]<<16 | z[2]<<8 | z[3];
+}
+
+static size_t zi_dotprod(const unsigned char *z, const unsigned char *v, size_t n)
+{
+	size_t y;
+	uint32_t x;
+	for (y=0; n; n--, z+=4, v++) {
+		x = zi_read32(z);
+		y += x * *v;
+	}
+	return y;
+}
+
+int __munmap(void *, size_t);
+
+static void do_tzset()
+{
+	char buf[NAME_MAX+25], *pathname=buf+24;
+	const char *try, *s;
+	const unsigned char *map = 0;
+	size_t i;
+	static const char search[] =
+		"/usr/share/zoneinfo/\0/share/zoneinfo/\0/etc/zoneinfo/\0";
+
+	s = getenv("TZ");
+	if (!s) s = "";
+
+	if (old_tz && !strcmp(s, old_tz)) return;
+
+	if (zi) __munmap((void *)zi, map_size);
+
+	/* Cache the old value of TZ to check if it has changed. Avoid
+	 * free so as not to pull it into static programs. Growth
+	 * strategy makes it so free would have minimal benefit anyway. */
+	i = strlen(s);
+	if (i > PATH_MAX+1) s = "", i = 0;
+	if (i >= old_tz_size) {
+		old_tz_size *= 2;
+		if (i >= old_tz_size) old_tz_size = i+1;
+		if (old_tz_size > PATH_MAX+2) old_tz_size = PATH_MAX+2;
+		old_tz = malloc(old_tz_size);
+	}
+	if (old_tz) memcpy(old_tz, s, i+1);
+
+	if (*s == ':') s++;
+
+	/* Non-suid can use an absolute tzfile pathname or a relative
+	 * pathame beginning with "."; in secure mode, only the
+	 * standard path will be searched. */
+	if (*s == '/' || *s == '.') {
+		if (!libc.secure) map = __map_file(s, &map_size);
+	} else {
+		for (i=0; s[i] && s[i]!=','; i++) {
+			if (s[i]=='/') {
+				size_t l = strlen(s);
+				if (l > NAME_MAX || strchr(s, '.'))
+					break;
+				memcpy(pathname, s, l+1);
+				pathname[l] = 0;
+				for (try=search; !map && *try; try+=l) {
+					l = strlen(try);
+					memcpy(pathname-l, try, l);
+					map = __map_file(pathname-l, &map_size);
+				}
+				break;
+			}
+		}
+	}
+
+	zi = map;
+	if (map) {
+		int scale = 2;
+		if (sizeof(time_t) > 4 && map[4]=='2') {
+			size_t skip = zi_dotprod(zi, VEC(1,1,8,5,6,1), 6);
+			trans = zi+skip+44+20;
+			scale++;
+		} else {
+			trans = zi+44;
+		}
+		index = trans + (zi_read32(trans-12) << scale);
+		types = index + zi_read32(trans-12);
+		abbrevs = types + 6*zi_read32(trans-8);
+		if (zi[map_size-1] == '\n') {
+			for (s = (const char *)zi+map_size-2; *s!='\n'; s--);
+			s++;
+		} else {
+			s = 0;
+		}
+	}
+
+	if (!s) s = "GMT0";
+	getname(std_name, &s);
+	__tzname[0] = std_name;
+	__timezone = getoff(&s);
+	getname(dst_name, &s);
+	__tzname[1] = dst_name;
+	if (dst_name[0]) {
+		__daylight = 1;
+		if (*s == '+' || *s=='-' || *s-'0'<10U)
+			dst_off = getoff(&s);
+		else
+			dst_off = __timezone - 3600;
+	} else {
+		__daylight = 0;
+		dst_off = 0;
+	}
+
+	if (*s == ',') s++, getrule(&s, r0);
+	if (*s == ',') s++, getrule(&s, r1);
+}
+
+/* Search zoneinfo rules to find the one that applies to the given time,
+ * and determine alternate opposite-DST-status rule that may be needed. */
+
+static size_t scan_trans(long long t, int local, size_t *alt)
+{
+	int scale = 3 - (trans == zi+44);
+	uint64_t x;
+	int off = 0;
+
+	size_t a = 0, n = (index-trans)>>scale, m;
+
+	if (!n) {
+		if (alt) *alt = 0;
+		return 0;
+	}
+
+	/* Binary search for 'most-recent rule before t'. */
+	while (n > 1) {
+		m = a + n/2;
+		x = zi_read32(trans + (m<<scale));
+		if (scale == 3) x = x<<32 | zi_read32(trans + (m<<scale) + 4);
+		else x = (int32_t)x;
+		if (local) off = (int32_t)zi_read32(types + 6 * index[m-1]);
+		if (t - off < (int64_t)x) {
+			n /= 2;
+		} else {
+			a = m;
+			n -= n/2;
+		}
+	}
+
+	/* First and last entry are special. First means to use lowest-index
+	 * non-DST type. Last means to apply POSIX-style rule if available. */
+	n = (index-trans)>>scale;
+	if (a == n-1) return -1;
+	if (a == 0) {
+		x = zi_read32(trans + (a<<scale));
+		if (scale == 3) x = x<<32 | zi_read32(trans + (a<<scale) + 4);
+		else x = (int32_t)x;
+		if (local) off = (int32_t)zi_read32(types + 6 * index[a-1]);
+		if (t - off < (int64_t)x) {
+			for (a=0; a<(abbrevs-types)/6; a++) {
+				if (types[6*a+4] != types[4]) break;
+			}
+			if (a == (abbrevs-types)/6) a = 0;
+			if (types[6*a+4]) {
+				*alt = a;
+				return 0;
+			} else {
+				*alt = 0;
+				return a;
+			}
+		}
+	}
+
+	/* Try to find a neighboring opposite-DST-status rule. */
+	if (alt) {
+		if (a && types[6*index[a-1]+4] != types[6*index[a]+4])
+			*alt = index[a-1];
+		else if (a+1<n && types[6*index[a+1]+4] != types[6*index[a]+4])
+			*alt = index[a+1];
+		else
+			*alt = index[a];
+	}
+
+	return index[a];
+}
+
+static int days_in_month(int m, int is_leap)
+{
+	if (m==2) return 28+is_leap;
+	else return 30+((0xad5>>(m-1))&1);
+}
+
+/* Convert a POSIX DST rule plus year to seconds since epoch. */
+
+static long long rule_to_secs(const int *rule, int year)
+{
+	int is_leap;
+	long long t = __year_to_secs(year, &is_leap);
+	int x, m, n, d;
+	if (rule[0]!='M') {
+		x = rule[1];
+		if (rule[0]=='J' && (x < 60 || !is_leap)) x--;
+		t += 86400 * x;
+	} else {
+		m = rule[1];
+		n = rule[2];
+		d = rule[3];
+		t += __month_to_secs(m-1, is_leap);
+		int wday = (int)((t + 4*86400) % (7*86400)) / 86400;
+		int days = d - wday;
+		if (days < 0) days += 7;
+		if (n == 5 && days+28 >= days_in_month(m, is_leap)) n = 4;
+		t += 86400 * (days + 7*(n-1));
+	}
+	t += rule[4];
+	return t;
+}
+
+/* Determine the time zone in effect for a given time in seconds since the
+ * epoch. It can be given in local or universal time. The results will
+ * indicate whether DST is in effect at the queried time, and will give both
+ * the GMT offset for the active zone/DST rule and the opposite DST. This
+ * enables a caller to efficiently adjust for the case where an explicit
+ * DST specification mismatches what would be in effect at the time. */
+
+void __secs_to_zone(long long t, int local, int *isdst, long *offset, long *oppoff, const char **zonename)
+{
+	LOCK(lock);
+
+	do_tzset();
+
+	if (zi) {
+		size_t alt, i = scan_trans(t, local, &alt);
+		if (i != -1) {
+			*isdst = types[6*i+4];
+			*offset = -(int32_t)zi_read32(types+6*i);
+			*zonename = (const char *)abbrevs + types[6*i+5];
+			if (oppoff) *oppoff = -(int32_t)zi_read32(types+6*alt);
+			UNLOCK(lock);
+			return;
+		}
+	}
+
+	if (!__daylight) goto std;
+
+	/* FIXME: may be broken if DST changes right at year boundary?
+	 * Also, this could be more efficient.*/
+	long long y = t / 31556952 + 70;
+	while (__year_to_secs(y, 0) > t) y--;
+	while (__year_to_secs(y+1, 0) < t) y++;
+
+	long long t0 = rule_to_secs(r0, y);
+	long long t1 = rule_to_secs(r1, y);
+
+	if (t0 < t1) {
+		if (!local) {
+			t0 += __timezone;
+			t1 += dst_off;
+		}
+		if (t >= t0 && t < t1) goto dst;
+		goto std;
+	} else {
+		if (!local) {
+			t1 += __timezone;
+			t0 += dst_off;
+		}
+		if (t >= t1 && t < t0) goto std;
+		goto dst;
+	}
+std:
+	*isdst = 0;
+	*offset = __timezone;
+	if (oppoff) *oppoff = dst_off;
+	*zonename = __tzname[0];
+	UNLOCK(lock);
+	return;
+dst:
+	*isdst = 1;
+	*offset = dst_off;
+	if (oppoff) *oppoff = __timezone;
+	*zonename = __tzname[1];
+	UNLOCK(lock);
+}
+
+void __tzset()
+{
+	LOCK(lock);
+	do_tzset();
+	UNLOCK(lock);
+}
+
+weak_alias(__tzset, tzset);