mtime: Minimize imprecision and prevent overflow on darwin.

[vlc] / src / misc / mtime.c

diff --git a/src/misc/mtime.c b/src/misc/mtime.c
index 7341a664b5ef68fd89380b6c4f52d4132f602916..115dbe9ffc6cce42a2ef2e9a5dde211a035b9fd1 100644 (file)
--- a/src/misc/mtime.c
+++ b/src/misc/mtime.c
@@ -214,13 +214,18 @@ mtime_t mdate( void )
 #elif defined( USE_APPLE_MACH )
     pthread_once(&mtime_timebase_info_once, mtime_init_timebase);
     uint64_t date = mach_absolute_time();
+    mach_timebase_info_data_t tb = mtime_timebase_info;
 
-    /* Convert to nanoseconds */
-    date *= mtime_timebase_info.numer;
-    date /= mtime_timebase_info.denom;
+    /* tb.denom is uint32_t, switch to 64 bits to prevent overflow. */
+    uint64_t denom = tb.denom;
 
-    /* Convert to microseconds */
-    res = date / 1000;
+    /* Switch to microsecs */
+    denom *= 1000LL;
+
+    /* Split the division to prevent overflow */
+    lldiv_t d = lldiv (tb.numer, denom);
+
+    res = (d.quot * date) + ((d.rem * date) / denom);
 
 #elif defined( WIN32 ) || defined( UNDER_CE )
     /* We don't need the real date, just the value of a high precision timer */