zig

commit 907c5589ae20d1b2a73acf26c9d67139dfe3bfb9 (tree)
parent cfe1fbad0f6a47fa0f5798df1423702b84bf34aa
Author: Heide Onas Auri <48419392+heidezomp@users.noreply.github.com>
Date:   Mon, 24 Feb 2020 00:25:52 +0100

std.time.Timer.lap: only read system time once (#4533)

Calling Timer.lap queried the system time twice; once to compute the lap
time and once to reset the timer. This can lead to time discrepancies
between actual and computed durations when summing the result of
Timer.lap in a loop. This commit fixes that.

also fix Timer.read to not require a pointer
Diffstat:
M
lib/std/time.zig
 | 
22
+++++++++++++---------

1 file changed, 13 insertions(+), 9 deletions(-)
diff --git a/lib/std/time.zig b/lib/std/time.zig
@@ -153,15 +153,9 @@ pub const Timer = struct {
     }
 
     /// Reads the timer value since start or the last reset in nanoseconds
-    pub fn read(self: *Timer) u64 {
+    pub fn read(self: Timer) u64 {
         var clock = clockNative() - self.start_time;
-        if (builtin.os == .windows) {
-            return @divFloor(clock * ns_per_s, self.frequency);
-        }
-        if (comptime std.Target.current.isDarwin()) {
-            return @divFloor(clock * self.frequency.numer, self.frequency.denom);
-        }
-        return clock;
+        return self.nativeDurationToNanos(clock);
     }
 
     /// Resets the timer value to 0/now.
@@ -172,7 +166,7 @@ pub const Timer = struct {
     /// Returns the current value of the timer in nanoseconds, then resets it
     pub fn lap(self: *Timer) u64 {
         var now = clockNative();
-        var lap_time = self.read();
+        var lap_time = self.nativeDurationToNanos(now - self.start_time);
         self.start_time = now;
         return lap_time;
     }
@@ -188,6 +182,16 @@ pub const Timer = struct {
         os.clock_gettime(monotonic_clock_id, &ts) catch unreachable;
         return @intCast(u64, ts.tv_sec) * @as(u64, ns_per_s) + @intCast(u64, ts.tv_nsec);
     }
+
+    fn nativeDurationToNanos(self: Timer, duration: u64) u64 {
+        if (builtin.os == .windows) {
+            return @divFloor(duration * ns_per_s, self.frequency);
+        }
+        if (comptime std.Target.current.isDarwin()) {
+            return @divFloor(duration * self.frequency.numer, self.frequency.denom);
+        }
+        return duration;
+    }
 };
 
 test "sleep" {