util: fix and move `get_current_time_msec` into a util file

This commit makes `get_current_time_msec` correctly return milliseconds
as opposed to microseconds. It also considers the value of `tv_sec`, so
we don't lose occasionally go back in time by one second. Finally, the
function is moved into `util/time.cc` so that it can be reused elsewhere
without having to consider these pitfalls.

backend/wayland/seat.c

@@ -20,6 +20,7 @@
 #include "relative-pointer-unstable-v1-client-protocol.h"
 #include "backend/wayland.h"
 #include "util/signal.h"
+#include "util/time.h"
 
 static struct wlr_wl_pointer *output_get_pointer(struct wlr_wl_output *output) {
 	struct wlr_input_device *wlr_dev;
@@ -197,12 +198,6 @@ static void keyboard_handle_keymap(void *data, struct wl_keyboard *wl_keyboard,
 	close(fd);
 }
 
-static uint32_t get_current_time_msec(void) {
-	struct timespec now;
-	clock_gettime(CLOCK_MONOTONIC, &now);
-	return now.tv_nsec / 1000;
-}
-
 static void keyboard_handle_enter(void *data, struct wl_keyboard *wl_keyboard,
 		uint32_t serial, struct wl_surface *surface, struct wl_array *keys) {
 	struct wlr_input_device *dev = data;

backend/wayland/tablet_v2.c

@@ -13,6 +13,7 @@
 #include <wlr/interfaces/wlr_input_device.h>
 
 #include "util/signal.h"
+#include "util/time.h"
 #include "wlr/util/log.h"
 #include "tablet-unstable-v2-client-protocol.h"
 
@@ -84,12 +85,6 @@ struct wlr_wl_tablet_pad_group {
 	struct wl_list strips; // wlr_wl_tablet_pad_strips::link
 };
 
-static uint32_t get_current_time_msec(void) {
-	struct timespec now;
-	clock_gettime(CLOCK_MONOTONIC, &now);
-	return now.tv_nsec / (1000 * 1000) + now.tv_sec * 1000;
-}
-
 static void handle_tablet_pad_ring_source(void *data,
 		struct zwp_tablet_pad_ring_v2 *zwp_tablet_pad_ring_v2,
 		uint32_t source) {

include/util/time.h

@@ -0,0 +1,9 @@
+#ifndef UTIL_TIME_H
+#define UTIL_TIME_H
+
+/**
+ * Get the current time, in milliseconds.
+ */
+uint32_t get_current_time_msec(void);
+
+#endif

util/meson.build

@@ -5,4 +5,5 @@ wlr_files += files(
 	'region.c',
 	'shm.c',
 	'signal.c',
+	'time.c',
 )

util/time.c

@@ -0,0 +1,11 @@
+#define _POSIX_C_SOURCE 200809L
+#include <stdint.h>
+#include <time.h>
+
+#include "util/time.h"
+
+uint32_t get_current_time_msec(void) {
+	struct timespec now;
+	clock_gettime(CLOCK_MONOTONIC, &now);
+	return now.tv_sec * 1000 + now.tv_nsec / 1000000;
+}