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[PATCH] NTP shift_right cleanup

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Create a macro shift_right() that avoids the numerous ugly conditionals in the
NTP code that look like:

        if(a < 0)
                b = -(-a >> shift);
        else
                b = a >> shift;

Replacing it with:

        b = shift_right(a, shift);

This should have zero effect on the logic, however it should probably have
a bit of testing just to be sure.

Also replace open-coded min/max with the macros.

Signed-off-by : John Stultz <johnstul@us.ibm.com>

Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
john stultz 2005-10-30 15:01:42 -08:00 committed by Linus Torvalds
parent 9c0cbd54ce
commit 1bb34a4127
3 changed files with 24 additions and 61 deletions
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7
include/linux/timex.h
View File

@ -282,6 +282,13 @@ static inline int ntp_synced(void)
return !(time_status & STA_UNSYNC);
}
/* Required to safely shift negative values */
#define shift_right(x, s) ({ \
__typeof__(x) __x = (x); \
__typeof__(s) __s = (s); \
__x < 0 ? -(-__x >> __s) : __x >> __s; \
})
#ifdef CONFIG_TIME_INTERPOLATION

25
kernel/time.c
View File

@ -338,30 +338,20 @@ int do_adjtimex(struct timex *txc)
if (mtemp >= MINSEC) {
ltemp = (time_offset / mtemp) << (SHIFT_USEC -
SHIFT_UPDATE);
if (ltemp < 0)
time_freq -= -ltemp >> SHIFT_KH;
else
time_freq += ltemp >> SHIFT_KH;
time_freq += shift_right(ltemp, SHIFT_KH);
} else /* calibration interval too short (p. 12) */
result = TIME_ERROR;
} else { /* PLL mode */
if (mtemp < MAXSEC) {
ltemp *= mtemp;
if (ltemp < 0)
time_freq -= -ltemp >> (time_constant +
time_constant +
SHIFT_KF - SHIFT_USEC);
else
time_freq += ltemp >> (time_constant +
time_freq += shift_right(ltemp,(time_constant +
time_constant +
SHIFT_KF - SHIFT_USEC);
SHIFT_KF - SHIFT_USEC));
} else /* calibration interval too long (p. 12) */
result = TIME_ERROR;
}
if (time_freq > time_tolerance)
time_freq = time_tolerance;
else if (time_freq < -time_tolerance)
time_freq = -time_tolerance;
time_freq = min(time_freq, time_tolerance);
time_freq = max(time_freq, -time_tolerance);
} /* STA_PLL || STA_PPSTIME */
} /* txc->modes & ADJ_OFFSET */
if (txc->modes & ADJ_TICK) {
@ -384,10 +374,7 @@ leave: if ((time_status & (STA_UNSYNC|STA_CLOCKERR)) != 0
if ((txc->modes & ADJ_OFFSET_SINGLESHOT) == ADJ_OFFSET_SINGLESHOT)
txc->offset = save_adjust;
else {
if (time_offset < 0)
txc->offset = -(-time_offset >> SHIFT_UPDATE);
else
txc->offset = time_offset >> SHIFT_UPDATE;
txc->offset = shift_right(time_offset, SHIFT_UPDATE);
}
txc->freq = time_freq + pps_freq;
txc->maxerror = time_maxerror;

53
kernel/timer.c
View File

@ -703,23 +703,13 @@ static void second_overflow(void)
* the adjustment over not more than the number of
* seconds between updates.
*/
if (time_offset < 0) {
ltemp = -time_offset;
if (!(time_status & STA_FLL))
ltemp >>= SHIFT_KG + time_constant;
if (ltemp > (MAXPHASE / MINSEC) << SHIFT_UPDATE)
ltemp = (MAXPHASE / MINSEC) << SHIFT_UPDATE;
time_offset += ltemp;
time_adj = -ltemp << (SHIFT_SCALE - SHIFT_HZ - SHIFT_UPDATE);
} else {
ltemp = time_offset;
if (!(time_status & STA_FLL))
ltemp >>= SHIFT_KG + time_constant;
if (ltemp > (MAXPHASE / MINSEC) << SHIFT_UPDATE)
ltemp = (MAXPHASE / MINSEC) << SHIFT_UPDATE;
ltemp = shift_right(ltemp, SHIFT_KG + time_constant);
ltemp = min(ltemp, (MAXPHASE / MINSEC) << SHIFT_UPDATE);
ltemp = max(ltemp, -(MAXPHASE / MINSEC) << SHIFT_UPDATE);
time_offset -= ltemp;
time_adj = ltemp << (SHIFT_SCALE - SHIFT_HZ - SHIFT_UPDATE);
}
/*
* Compute the frequency estimate and additional phase
@ -736,39 +726,25 @@ static void second_overflow(void)
STA_PPSWANDER | STA_PPSERROR);
}
ltemp = time_freq + pps_freq;
if (ltemp < 0)
time_adj -= -ltemp >>
(SHIFT_USEC + SHIFT_HZ - SHIFT_SCALE);
else
time_adj += ltemp >>
(SHIFT_USEC + SHIFT_HZ - SHIFT_SCALE);
time_adj += shift_right(ltemp,(SHIFT_USEC + SHIFT_HZ - SHIFT_SCALE));
#if HZ == 100
/* Compensate for (HZ==100) != (1 << SHIFT_HZ).
* Add 25% and 3.125% to get 128.125; => only 0.125% error (p. 14)
*/
if (time_adj < 0)
time_adj -= (-time_adj >> 2) + (-time_adj >> 5);
else
time_adj += (time_adj >> 2) + (time_adj >> 5);
time_adj += shift_right(time_adj, 2) + shift_right(time_adj, 5);
#endif
#if HZ == 250
/* Compensate for (HZ==250) != (1 << SHIFT_HZ).
* Add 1.5625% and 0.78125% to get 255.85938; => only 0.05% error (p. 14)
*/
if (time_adj < 0)
time_adj -= (-time_adj >> 6) + (-time_adj >> 7);
else
time_adj += (time_adj >> 6) + (time_adj >> 7);
time_adj += shift_right(time_adj, 6) + shift_right(time_adj, 7);
#endif
#if HZ == 1000
/* Compensate for (HZ==1000) != (1 << SHIFT_HZ).
* Add 1.5625% and 0.78125% to get 1023.4375; => only 0.05% error (p. 14)
*/
if (time_adj < 0)
time_adj -= (-time_adj >> 6) + (-time_adj >> 7);
else
time_adj += (time_adj >> 6) + (time_adj >> 7);
time_adj += shift_right(time_adj, 6) + shift_right(time_adj, 7);
#endif
}
@ -787,10 +763,8 @@ static void update_wall_time_one_tick(void)
* Limit the amount of the step to be in the range
* -tickadj .. +tickadj
*/
if (time_adjust > tickadj)
time_adjust_step = tickadj;
else if (time_adjust < -tickadj)
time_adjust_step = -tickadj;
time_adjust_step = min(time_adjust_step, (long)tickadj);
time_adjust_step = max(time_adjust_step, (long)-tickadj);
/* Reduce by this step the amount of time left */
time_adjust -= time_adjust_step;
@ -801,13 +775,8 @@ static void update_wall_time_one_tick(void)
* advance the tick more.
*/
time_phase += time_adj;
if (time_phase <= -FINENSEC) {
long ltemp = -time_phase >> (SHIFT_SCALE - 10);
time_phase += ltemp << (SHIFT_SCALE - 10);
delta_nsec -= ltemp;
}
else if (time_phase >= FINENSEC) {
long ltemp = time_phase >> (SHIFT_SCALE - 10);
if ((time_phase >= FINENSEC) || (time_phase <= -FINENSEC)) {
long ltemp = shift_right(time_phase, (SHIFT_SCALE - 10));
time_phase -= ltemp << (SHIFT_SCALE - 10);
delta_nsec += ltemp;
}