Messages in this thread Patch in this message | | | Subject | [RFC][PATCH - 7/12] NTP cleanup: Cleanup signed shifting logic | From | john stultz <> | Date | Fri, 15 Jul 2005 20:04:23 -0700 |
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All, Signed shifting must be done carefully, and the ntp code has quite a number of conditionals to do the signed shifting. This patch makes use of the local shiftR() macro introduced in a previous patch to simplify a bit of logic.
Any comments or feedback would be greatly appreciated.
thanks -john
linux-2.6.13-rc3_timeofday-ntp-part7_B4.patch ============================================ diff --git a/kernel/ntp.c b/kernel/ntp.c --- a/kernel/ntp.c +++ b/kernel/ntp.c @@ -165,28 +165,19 @@ void second_overflow(void) } ltemp = time_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 += shiftR(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 += shiftR(time_adj,2) + shiftR(time_adj,5); #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 += shiftR(time_adj,6) + shiftR(time_adj,7); #endif } @@ -352,10 +343,7 @@ int ntp_adjtimex(struct timex *txc) 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 = shiftR(time_offset, SHIFT_UPDATE); } txc->freq = time_freq; txc->maxerror = time_maxerror;
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