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authorMartin Schwidefsky <schwidefsky@de.ibm.com>2017-03-01 09:47:57 +0100
committerMartin Schwidefsky <schwidefsky@de.ibm.com>2017-03-01 09:59:28 +0100
commitd03bd0454b101adb94d0b5a9cc11396182943cb4 (patch)
tree1ff875a7337cbbd3ba85f8990e3d4103139c41cf /arch/s390
parente53051e757d6cd66741955b93581e54415e48a70 (diff)
downloadlinux-d03bd0454b101adb94d0b5a9cc11396182943cb4.tar.bz2
s390/timex: micro optimization for tod_to_ns
The conversion of a TOD value to nano-seconds currently uses a 32/32 bit split with the calculation for "nsecs = (TOD * 125) >> 9". Using a 55/9 bit split saves an instruction. Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Diffstat (limited to 'arch/s390')
-rw-r--r--arch/s390/include/asm/timex.h12
1 files changed, 4 insertions, 8 deletions
diff --git a/arch/s390/include/asm/timex.h b/arch/s390/include/asm/timex.h
index 354344dcc198..118535123f34 100644
--- a/arch/s390/include/asm/timex.h
+++ b/arch/s390/include/asm/timex.h
@@ -206,20 +206,16 @@ static inline unsigned long long get_tod_clock_monotonic(void)
* ns = (todval * 125) >> 9;
*
* In order to avoid an overflow with the multiplication we can rewrite this.
- * With a split todval == 2^32 * th + tl (th upper 32 bits, tl lower 32 bits)
+ * With a split todval == 2^9 * th + tl (th upper 55 bits, tl lower 9 bits)
* we end up with
*
- * ns = ((2^32 * th + tl) * 125 ) >> 9;
- * -> ns = (2^23 * th * 125) + ((tl * 125) >> 9);
+ * ns = ((2^9 * th + tl) * 125 ) >> 9;
+ * -> ns = (th * 125) + ((tl * 125) >> 9);
*
*/
static inline unsigned long long tod_to_ns(unsigned long long todval)
{
- unsigned long long ns;
-
- ns = ((todval >> 32) << 23) * 125;
- ns += ((todval & 0xffffffff) * 125) >> 9;
- return ns;
+ return ((todval >> 9) * 125) + (((todval & 0x1ff) * 125) >> 9);
}
#endif