[PATCH] Time: optimize out some mults, since gcc can't avoid them

Newsflash: GCC not as smart as once hoped.

This patch removes some mults since GCC can't figure out how.

Pointed out by Roman Zippel.

Signed-off-by: John Stultz <johnstul@xxxxxxxxxx>

diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h
index 585789f..5f4a7f7 100644
--- a/include/linux/clocksource.h
+++ b/include/linux/clocksource.h
@@ -236,7 +236,6 @@ static inline int error_aproximation(u64
*
* Where mult_delta is the adjustment value made to mult
*
- * XXX - Hopefully gcc is smart enough to avoid the multiplies.
*/
static inline s64 make_ntp_adj(struct clocksource *clock,
cycles_t cycles_delta, s64* error)
@@ -244,27 +243,27 @@ static inline s64 make_ntp_adj(struct cl
s64 ret = 0;
if (*error > ((s64)clock->interval_cycles+1)/2) {
/* calculate adjustment value */
- int adjustment = 1 << error_aproximation(*error,
+ int adjustment = error_aproximation(*error,
clock->interval_cycles);
/* adjust clock */
- clock->mult += adjustment;
- clock->interval_snsecs += clock->interval_cycles * adjustment;
+ clock->mult += 1 << adjustment;
+ clock->interval_snsecs += clock->interval_cycles << adjustment;

/* adjust the base and error for the adjustment */
- ret = -(cycles_delta * adjustment);
- *error -= clock->interval_cycles * adjustment;
+ ret = -(cycles_delta << adjustment);
+ *error -= clock->interval_cycles << adjustment;
/* XXX adj error for cycle_delta offset? */
} else if ((-(*error)) > ((s64)clock->interval_cycles+1)/2) {
/* calculate adjustment value */
- int adjustment = 1 << error_aproximation(-(*error),
+ int adjustment = error_aproximation(-(*error),
clock->interval_cycles);
/* adjust clock */
- clock->mult -= adjustment;
- clock->interval_snsecs -= clock->interval_cycles * adjustment;
+ clock->mult -= 1 << adjustment;
+ clock->interval_snsecs -= clock->interval_cycles << adjustment;

/* adjust the base and error for the adjustment */
- ret = cycles_delta * adjustment;
- *error += clock->interval_cycles * adjustment;
+ ret = cycles_delta << adjustment;
+ *error += clock->interval_cycles << adjustment;
/* XXX adj error for cycle_delta offset? */
}
return ret;


-
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