time-util: rename usec_sub() to usec_sub_signed() and add usec_sub_unsigned()

Quite often we just want to subtract two normal usec_t values, hence
provide an implementation for that.

4 files changed, 49 insertions, 23 deletions

diff --git a/src/basic/time-util.c b/src/basic/time-util.c
index 8d55af8492..51b06698ad 100644
--- a/src/basic/time-util.c
+++ b/src/basic/time-util.c
@@ -107,7 +107,7 @@ dual_timestamp* dual_timestamp_from_realtime(dual_timestamp *ts, usec_t u) {
         ts->realtime = u;
 
         delta = (int64_t) now(CLOCK_REALTIME) - (int64_t) u;
-        ts->monotonic = usec_sub(now(CLOCK_MONOTONIC), delta);
+        ts->monotonic = usec_sub_signed(now(CLOCK_MONOTONIC), delta);
 
         return ts;
 }
@@ -124,8 +124,8 @@ triple_timestamp* triple_timestamp_from_realtime(triple_timestamp *ts, usec_t u)
 
         ts->realtime = u;
         delta = (int64_t) now(CLOCK_REALTIME) - (int64_t) u;
-        ts->monotonic = usec_sub(now(CLOCK_MONOTONIC), delta);
-        ts->boottime = clock_boottime_supported() ? usec_sub(now(CLOCK_BOOTTIME), delta) : USEC_INFINITY;
+        ts->monotonic = usec_sub_signed(now(CLOCK_MONOTONIC), delta);
+        ts->boottime = clock_boottime_supported() ? usec_sub_signed(now(CLOCK_BOOTTIME), delta) : USEC_INFINITY;
 
         return ts;
 }
@@ -141,7 +141,7 @@ dual_timestamp* dual_timestamp_from_monotonic(dual_timestamp *ts, usec_t u) {
 
         ts->monotonic = u;
         delta = (int64_t) now(CLOCK_MONOTONIC) - (int64_t) u;
-        ts->realtime = usec_sub(now(CLOCK_REALTIME), delta);
+        ts->realtime = usec_sub_signed(now(CLOCK_REALTIME), delta);
 
         return ts;
 }
@@ -156,8 +156,8 @@ dual_timestamp* dual_timestamp_from_boottime_or_monotonic(dual_timestamp *ts, us
 
         dual_timestamp_get(ts);
         delta = (int64_t) now(clock_boottime_or_monotonic()) - (int64_t) u;
-        ts->realtime = usec_sub(ts->realtime, delta);
-        ts->monotonic = usec_sub(ts->monotonic, delta);
+        ts->realtime = usec_sub_signed(ts->realtime, delta);
+        ts->monotonic = usec_sub_signed(ts->monotonic, delta);
 
         return ts;
 }
diff --git a/src/basic/time-util.h b/src/basic/time-util.h
index 7463507f51..8e2715cf68 100644
--- a/src/basic/time-util.h
+++ b/src/basic/time-util.h
@@ -169,19 +169,23 @@ static inline usec_t usec_add(usec_t a, usec_t b) {
         return c;
 }
 
-static inline usec_t usec_sub(usec_t timestamp, int64_t delta) {
-        if (delta < 0)
-                return usec_add(timestamp, (usec_t) (-delta));
+static inline usec_t usec_sub_unsigned(usec_t timestamp, usec_t delta) {
 
         if (timestamp == USEC_INFINITY) /* Make sure infinity doesn't degrade */
                 return USEC_INFINITY;
-
-        if (timestamp < (usec_t) delta)
+        if (timestamp < delta)
                 return 0;
 
         return timestamp - delta;
 }
 
+static inline usec_t usec_sub_signed(usec_t timestamp, int64_t delta) {
+        if (delta < 0)
+                return usec_add(timestamp, (usec_t) (-delta));
+        else
+                return usec_sub_unsigned(timestamp, (usec_t) delta);
+}
+
 #if SIZEOF_TIME_T == 8
 /* The last second we can format is 31. Dec 9999, 1s before midnight, because otherwise we'd enter 5 digit year
  * territory. However, since we want to stay away from this in all timezones we take one day off. */
diff --git a/src/journal-remote/journal-upload-journal.c b/src/journal-remote/journal-upload-journal.c
index 8ce8e1895e..3a36e46ae0 100644
--- a/src/journal-remote/journal-upload-journal.c
+++ b/src/journal-remote/journal-upload-journal.c
@@ -251,7 +251,7 @@ static inline void check_update_watchdog(Uploader *u) {
                 return;
 
         after = now(CLOCK_MONOTONIC);
-        elapsed_time = usec_sub(after, u->watchdog_timestamp);
+        elapsed_time = usec_sub_unsigned(after, u->watchdog_timestamp);
         if (elapsed_time > u->watchdog_usec / 2) {
                 log_debug("Update watchdog timer");
                 sd_notify(false, "WATCHDOG=1");
diff --git a/src/test/test-time.c b/src/test/test-time.c
index c9e31e90e1..5523263e76 100644
--- a/src/test/test-time.c
+++ b/src/test/test-time.c
@@ -195,16 +195,37 @@ static void test_usec_add(void) {
         assert_se(usec_add(USEC_INFINITY, 2) == USEC_INFINITY);
 }
 
-static void test_usec_sub(void) {
-        assert_se(usec_sub(0, 0) == 0);
-        assert_se(usec_sub(4, 1) == 3);
-        assert_se(usec_sub(4, 4) == 0);
-        assert_se(usec_sub(4, 5) == 0);
-        assert_se(usec_sub(USEC_INFINITY-3, -3) == USEC_INFINITY);
-        assert_se(usec_sub(USEC_INFINITY-3, -3) == USEC_INFINITY);
-        assert_se(usec_sub(USEC_INFINITY-3, -4) == USEC_INFINITY);
-        assert_se(usec_sub(USEC_INFINITY-3, -5) == USEC_INFINITY);
-        assert_se(usec_sub(USEC_INFINITY, 5) == USEC_INFINITY);
+static void test_usec_sub_unsigned(void) {
+        assert_se(usec_sub_unsigned(0, 0) == 0);
+        assert_se(usec_sub_unsigned(0, 2) == 0);
+        assert_se(usec_sub_unsigned(0, USEC_INFINITY) == 0);
+        assert_se(usec_sub_unsigned(1, 0) == 1);
+        assert_se(usec_sub_unsigned(1, 1) == 0);
+        assert_se(usec_sub_unsigned(1, 2) == 0);
+        assert_se(usec_sub_unsigned(1, 3) == 0);
+        assert_se(usec_sub_unsigned(1, USEC_INFINITY) == 0);
+        assert_se(usec_sub_unsigned(USEC_INFINITY-1, 0) == USEC_INFINITY-1);
+        assert_se(usec_sub_unsigned(USEC_INFINITY-1, 1) == USEC_INFINITY-2);
+        assert_se(usec_sub_unsigned(USEC_INFINITY-1, 2) == USEC_INFINITY-3);
+        assert_se(usec_sub_unsigned(USEC_INFINITY-1, USEC_INFINITY-2) == 1);
+        assert_se(usec_sub_unsigned(USEC_INFINITY-1, USEC_INFINITY-1) == 0);
+        assert_se(usec_sub_unsigned(USEC_INFINITY-1, USEC_INFINITY) == 0);
+        assert_se(usec_sub_unsigned(USEC_INFINITY, 0) == USEC_INFINITY);
+        assert_se(usec_sub_unsigned(USEC_INFINITY, 1) == USEC_INFINITY);
+        assert_se(usec_sub_unsigned(USEC_INFINITY, 2) == USEC_INFINITY);
+        assert_se(usec_sub_unsigned(USEC_INFINITY, USEC_INFINITY) == USEC_INFINITY);
+}
+
+static void test_usec_sub_signed(void) {
+        assert_se(usec_sub_signed(0, 0) == 0);
+        assert_se(usec_sub_signed(4, 1) == 3);
+        assert_se(usec_sub_signed(4, 4) == 0);
+        assert_se(usec_sub_signed(4, 5) == 0);
+        assert_se(usec_sub_signed(USEC_INFINITY-3, -3) == USEC_INFINITY);
+        assert_se(usec_sub_signed(USEC_INFINITY-3, -3) == USEC_INFINITY);
+        assert_se(usec_sub_signed(USEC_INFINITY-3, -4) == USEC_INFINITY);
+        assert_se(usec_sub_signed(USEC_INFINITY-3, -5) == USEC_INFINITY);
+        assert_se(usec_sub_signed(USEC_INFINITY, 5) == USEC_INFINITY);
 }
 
 static void test_format_timestamp(void) {
@@ -322,7 +343,8 @@ int main(int argc, char *argv[]) {
         test_timezone_is_valid();
         test_get_timezones();
         test_usec_add();
-        test_usec_sub();
+        test_usec_sub_signed();
+        test_usec_sub_unsigned();
         test_format_timestamp();
         test_format_timestamp_utc();
         test_dual_timestamp_deserialize();