tile: avoid overflow in ns2cycles

[sfrench/cifs-2.6.git] / arch / tile / kernel / time.c

diff --git a/arch/tile/kernel/time.c b/arch/tile/kernel/time.c
index 5d10642db63e8e9f98934e36200128a9dfd26073..462dcd0c1700221adda93563b5f7904511a9c656 100644 (file)
--- a/arch/tile/kernel/time.c
+++ b/arch/tile/kernel/time.c
@@ -236,7 +236,15 @@ cycles_t ns2cycles(unsigned long nsecs)
         * clock frequency.
         */
        struct clock_event_device *dev = &__raw_get_cpu_var(tile_timer);
-       return ((u64)nsecs * dev->mult) >> dev->shift;
+
+       /*
+        * as in clocksource.h and x86's timer.h, we split the calculation
+        * into 2 parts to avoid unecessary overflow of the intermediate
+        * value. This will not lead to any loss of precision.
+        */
+       u64 quot = (u64)nsecs >> dev->shift;
+       u64 rem  = (u64)nsecs & ((1ULL << dev->shift) - 1);
+       return quot * dev->mult + ((rem * dev->mult) >> dev->shift);
 }
 
 void update_vsyscall_tz(void)