Switched the macOS code to use timerprivInt128ToUint64(). Also rearranged the arguments of timerprivInt128ToInt64() and added proper timerDurationMin/Max constants instead of the incorrect-for-that-function timerTimeMin/Max in the Windows code.

test/initmain.c

@@ -53,6 +53,12 @@ struct testParams {
 	timerSysError err;
 };
 
+/*
+TODO if I remove the uiQuit() from this test on Windows, I will occasionally get
+=== RUN   TestQueueMain_DifferentThread
+    ../test/initmain.c:161: uiMain() timed out (5s)
+--- FAIL: TestQueueMain_DifferentThread (4.9989539s)
+*/
 static void queued(void *data)
 {
 	struct testParams *p = (struct testParams *) data;
@@ -147,12 +153,6 @@ static void queueThread(void *data)
 	uiQueueMain(queued, p);
 }
 
-/*
-TODO if I remove the uiQuit() from this test on Windows, I will occasionally get
-=== RUN   TestQueueMain_DifferentThread
-    ../test/initmain.c:161: uiMain() timed out (5s)
---- FAIL: TestQueueMain_DifferentThread (4.9989539s)
-*/
 testingTest(QueueMain_DifferentThread)
 {
 	threadThread *thread;

test/lib/timer.c

@@ -306,7 +306,7 @@ void timerprivMulDivUint64(uint64_t x, uint64_t y, uint64_t z, timerprivInt128 *
 	int128MulDiv64(&a, &b, &c, quot);
 }
 
-int64_t timerprivInt128ToInt64(const timerprivInt128 *n, int64_t min, int64_t max, int64_t minCap, int64_t maxCap)
+int64_t timerprivInt128ToInt64(const timerprivInt128 *n, int64_t min, int64_t minCap, int64_t max, int64_t maxCap)
 {
 	if (n->neg) {
 		int64_t ret;
@@ -347,6 +347,9 @@ uint64_t timerprivInt128ToUint64(const timerprivInt128 *n, uint64_t max, uint64_
 {
 	if (n->neg)
 		return 0;
-	// TODO
-	return 0;
+	if (n->high != 0)
+		return maxCap;
+	if (n->low > maxCap)
+		return maxCap;
+	return n->low;
 }

test/lib/timer.h

@@ -5,8 +5,9 @@
 typedef int64_t timerDuration;
 typedef int64_t timerTime;
 
-#define timerTimeMin ((timerTime) INT64_MIN)
 #define timerTimeMax ((timerTime) INT64_MAX)
+#define timerDurationMin ((timerDuration) INT64_MIN)
+#define timerDurationMax ((timerDuration) INT64_MAX)
 
 #define timerNanosecond ((timerDuration) 1)
 #define timerMicrosecond ((timerDuration) 1000)

test/lib/timer_darwinunix.c

@@ -55,10 +55,9 @@ timerTime timerMonotonicNow(void)
 	t = mach_absolute_time() - base;
 	timerprivMulDivUint64(t, mt.numer, mt.denom, &quot);
 	// on overflow, return the maximum possible timerTime; this is inspired by what Go does
-	if (quot.high == 0)
-		if (quot.low <= ((uint64_t) timerTimeMax))
-			return (timerTime) (quot.low);
-	return timerTimeMax;
+	// the limit check will ensure we can safely cast the return value to a timerTime
+	return (timerTime) timerprivInt128ToUint64(&quot,
+		(uint64_t) timerTimeMax, (uint64_t) timerTimeMax);
 }
 
 #else

test/lib/timer_windows.c

@@ -186,9 +186,10 @@ timerDuration timerTimeSub(timerTime end, timerTime start)
 
 	QueryPerformanceFrequency(&qpf);
 	timerprivMulDivInt64(end - start, timerSecond, qpf.QuadPart, &quot);
+	// on underflow/overflow, return the minimum/maximum possible timerDuration (respectively); this is based on what Go does
 	return timerprivInt128ToInt64(&quot,
-		INT64_MIN, INT64_MAX,
-		timerTimeMin, timerTimeMax);
+		INT64_MIN, timerDurationMin,
+		INT64_MAX, timerDurationMax);
 }
 
 // note: the idea for the SetThreadContext() nuttery is from https://www.codeproject.com/Articles/71529/Exception-Injection-Throwing-an-Exception-in-Other

test/lib/timerpriv.h

@@ -10,5 +10,5 @@ struct timerprivInt128 {
 
 extern void timerprivMulDivInt64(int64_t x, int64_t y, int64_t z, timerprivInt128 *quot);
 extern void timerprivMulDivUint64(uint64_t x, uint64_t y, uint64_t z, timerprivInt128 *quot);
-extern int64_t timerprivInt128ToInt64(const timerprivInt128 *n, int64_t min, int64_t max, int64_t minCap, int64_t maxCap);
+extern int64_t timerprivInt128ToInt64(const timerprivInt128 *n, int64_t min, int64_t minCap, int64_t max, int64_t maxCap);
 extern uint64_t timerprivInt128ToUint64(const timerprivInt128 *n, uint64_t max, uint64_t maxCap);