Messages in this thread Patch in this message | | | Subject | [PATCH] Time: optimize out some mults, since gcc can't avoid them | From | john stultz <> | Date | Fri, 05 May 2006 18:44:33 -0700 |
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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@us.ibm.com>
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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