From 60a33ca726518a3325e56d77f65bfdcbecf91444 Mon Sep 17 00:00:00 2001
From: Tavian Barnes <tavianator@tavianator.com>
Date: Tue, 11 Feb 2020 22:20:57 -0500
Subject: Implement explicit reference times (-newerXt)

---
 util.c | 54 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 54 insertions(+)

(limited to 'util.c')

diff --git a/util.c b/util.c
index 691402c..88f90aa 100644
--- a/util.c
+++ b/util.c
@@ -174,6 +174,60 @@ int xlocaltime(const time_t *timep, struct tm *result) {
 	}
 }
 
+int xgmtime(const time_t *timep, struct tm *result) {
+	// Should be called before gmtime_r() according to POSIX.1-2004
+	tzset();
+
+	if (gmtime_r(timep, result)) {
+		return 0;
+	} else {
+		return -1;
+	}
+}
+
+time_t xtimegm(struct tm *tm) {
+	// Some man pages for timegm() recommend this as a portable approach
+	time_t ret = -1;
+	int error;
+
+	char *old_tz = getenv("TZ");
+	if (old_tz) {
+		old_tz = strdup(old_tz);
+		if (!old_tz) {
+			error = errno;
+			goto fail;
+		}
+	}
+
+	if (setenv("TZ", "UTC0", true) != 0) {
+		error = errno;
+		goto fail;
+	}
+
+	ret = mktime(tm);
+	error = errno;
+
+	if (old_tz) {
+		if (setenv("TZ", old_tz, true) != 0) {
+			ret = -1;
+			error = errno;
+			goto fail;
+		}
+	} else {
+		if (unsetenv("TZ") != 0) {
+			ret = -1;
+			error = errno;
+			goto fail;
+		}
+	}
+
+	tzset();
+fail:
+	free(old_tz);
+	errno = error;
+	return ret;
+}
+
 void format_mode(mode_t mode, char str[11]) {
 	strcpy(str, "----------");
 
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