From f976c98d334dce9ba30aa7da4427bb530aeea536 Mon Sep 17 00:00:00 2001
From: Tavian Barnes <tavianator@tavianator.com>
Date: Mon, 6 May 2024 16:04:05 -0400
Subject: xtime: Use the libc's timegm() if present

---
 build/has/timegm.c |  9 +++++++++
 build/header.mk    |  1 +
 src/xtime.c        | 36 +++++++++++++++++++++++++++++++++---
 tests/xtime.c      | 12 ++++++++----
 4 files changed, 51 insertions(+), 7 deletions(-)
 create mode 100644 build/has/timegm.c

diff --git a/build/has/timegm.c b/build/has/timegm.c
new file mode 100644
index 0000000..6e2d155
--- /dev/null
+++ b/build/has/timegm.c
@@ -0,0 +1,9 @@
+// Copyright © Tavian Barnes <tavianator@tavianator.com>
+// SPDX-License-Identifier: 0BSD
+
+#include <time.h>
+
+int main(void) {
+	struct tm tm = {0};
+	return (int)timegm(&tm);
+}
diff --git a/build/header.mk b/build/header.mk
index a9157ad..d235fd0 100644
--- a/build/header.mk
+++ b/build/header.mk
@@ -40,6 +40,7 @@ HEADERS := \
     gen/has/strerror-l.h \
     gen/has/strerror-r-gnu.h \
     gen/has/strerror-r-posix.h \
+    gen/has/timegm.h \
     gen/has/tm-gmtoff.h \
     gen/has/uselocale.h
 
diff --git a/src/xtime.c b/src/xtime.c
index 91ed915..c3537e7 100644
--- a/src/xtime.c
+++ b/src/xtime.c
@@ -12,13 +12,13 @@
 #include <unistd.h>
 
 int xmktime(struct tm *tm, time_t *timep) {
-	*timep = mktime(tm);
+	time_t time = mktime(tm);
 
-	if (*timep == -1) {
+	if (time == -1) {
 		int error = errno;
 
 		struct tm tmp;
-		if (!localtime_r(timep, &tmp)) {
+		if (!localtime_r(&time, &tmp)) {
 			bfs_bug("localtime_r(-1): %s", xstrerror(errno));
 			return -1;
 		}
@@ -30,9 +30,37 @@ int xmktime(struct tm *tm, time_t *timep) {
 		}
 	}
 
+	*timep = time;
+	return 0;
+}
+
+#if BFS_HAS_TIMEGM
+
+int xtimegm(struct tm *tm, time_t *timep) {
+	time_t time = timegm(tm);
+
+	if (time == -1) {
+		int error = errno;
+
+		struct tm tmp;
+		if (!gmtime_r(&time, &tmp)) {
+			bfs_bug("gmtime_r(-1): %s", xstrerror(errno));
+			return -1;
+		}
+
+		if (tm->tm_year != tmp.tm_year || tm->tm_yday != tmp.tm_yday
+		    || tm->tm_hour != tmp.tm_hour || tm->tm_min != tmp.tm_min || tm->tm_sec != tmp.tm_sec) {
+			errno = error;
+			return -1;
+		}
+	}
+
+	*timep = time;
 	return 0;
 }
 
+#else
+
 static int safe_add(int *value, int delta) {
 	if (*value >= 0) {
 		if (delta > INT_MAX - *value) {
@@ -147,6 +175,8 @@ overflow:
 	return -1;
 }
 
+#endif // !BFS_HAS_TIMEGM
+
 /** Parse a decimal digit. */
 static int xgetdigit(char c) {
 	int ret = c - '0';
diff --git a/tests/xtime.c b/tests/xtime.c
index a7c63d2..d9d6c5c 100644
--- a/tests/xtime.c
+++ b/tests/xtime.c
@@ -137,6 +137,7 @@ static bool check_one_xtimegm(const struct tm *tm) {
 	return ret;
 }
 
+#if !BFS_HAS_TIMEGM
 /** Check an overflowing xtimegm() call. */
 static bool check_xtimegm_overflow(const struct tm *tm) {
 	struct tm copy = *tm;
@@ -154,6 +155,7 @@ static bool check_xtimegm_overflow(const struct tm *tm) {
 
 	return ret;
 }
+#endif
 
 /** xtimegm() tests. */
 static bool check_xtimegm(void) {
@@ -173,11 +175,13 @@ static bool check_xtimegm(void) {
 		ret &= check_one_xtimegm(&tm);
 	}
 
+#if !BFS_HAS_TIMEGM
 	// Check integer overflow cases
-	check_xtimegm_overflow(&(struct tm) { .tm_sec = INT_MAX, .tm_min = INT_MAX });
-	check_xtimegm_overflow(&(struct tm) { .tm_min = INT_MAX, .tm_hour = INT_MAX });
-	check_xtimegm_overflow(&(struct tm) { .tm_hour = INT_MAX, .tm_mday = INT_MAX });
-	check_xtimegm_overflow(&(struct tm) { .tm_mon = INT_MAX, .tm_year = INT_MAX });
+	ret &= check_xtimegm_overflow(&(struct tm) { .tm_sec = INT_MAX, .tm_min = INT_MAX });
+	ret &= check_xtimegm_overflow(&(struct tm) { .tm_min = INT_MAX, .tm_hour = INT_MAX });
+	ret &= check_xtimegm_overflow(&(struct tm) { .tm_hour = INT_MAX, .tm_mday = INT_MAX });
+	ret &= check_xtimegm_overflow(&(struct tm) { .tm_mon = INT_MAX, .tm_year = INT_MAX });
+#endif
 
 	return ret;
 }
-- 
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