1999/0421/port/tod.c (diff list | history)

1999/0227/sys/src/9/port/tod.c:31,41 – 1999/0421/sys/src/9/port/tod.c:31,41 (short | long | prev | next)
1999/0225		// constraints: // // 1) log2(1000000000<<s1) <= 63 // or s1 <= 33 // 2) accomodate 15 minutes of ticks without overflow // or log2(((1000000000<<s1)/f)*((15*60*f)>>s2)) <= 63 // or log2(mult) + 12 + log2(f) - s2 <= 63 // or log2(mult) + log2(f) - 51 <= s2
1999/0421		// or s1 <= 32 // 2) accomodate 1 minute of ticks without overflow // or log2(((1000000000<<s1)/f)*((60*f)>>s2)) <= 63 // or log2(mult) + 6 + log2(f) - s2 <= 63 // or log2(mult) + log2(f) - 57 <= s2
1999/0225		// // by definition //
1999/0227/sys/src/9/port/tod.c:50,58 – 1999/0421/sys/src/9/port/tod.c:50,58
1999/0225		// // Combining 2) and 4) we get // // 5) log2(f) - s2 + log2(f) - 51 <= s2 // or 2*log2(f) - 51 <= 2*s2 // or log2(f) - 25 <= s2
1999/0421		// 5) log2(f) - s2 + log2(f) - 57 <= s2 // or 2*log2(f) - 57 <= 2*s2 // or log2(f) - 28 <= s2
1999/0225		// // Combining 3) and 4) //
1999/0227/sys/src/9/port/tod.c:74,91 – 1999/0421/sys/src/9/port/tod.c:74,91
1999/0225		// // for f = 267000000, log2(f) = 28 // // s2 = 3 // s1 = 23
1999/0421		// s2 = 0 // s1 = 26
1999/0225		// // for f = 2000000000, log2(f) = 31 // // s2 = 6 // s1 = 26
1999/0421		// s2 = 3 // s1 = 29
1999/0225		// // for f = 8000000000, log2(f) = 33 // // s2 = 8 // s1 = 28
1999/0421		// s2 = 5 // s1 = 31
1999/0219		// frequency of the tod clock #define TODFREQ 1000000000LL
1999/0227/sys/src/9/port/tod.c:97,103 – 1999/0421/sys/src/9/port/tod.c:97,102
1999/0225		int s1; // time = ((ticks>>s2)*multiplier)>>(s1-s2)
1999/0219		vlong multiplier; // ...
1999/0225		int s2; // ... vlong maxdiff; // max diff between ticks and last to avoid overflow
1999/0219		vlong hz; // frequency of fast clock vlong last; // last reading of fast clock vlong off; // offset from epoch to last
1999/0227/sys/src/9/port/tod.c:148,163 – 1999/0421/sys/src/9/port/tod.c:147,161
1999/0219		ilock(&tod); tod.hz = f;
1999/0225		lf = log2(f); tod.s2 = lf - 25;
1999/0421		tod.s2 = lf - 28;
1999/0225		if(tod.s2 < 0) tod.s2 = 0; tod.s1 = 2*lf - tod.s2 - 30; if(tod.s1 < 0) tod.s1 = 0; if(tod.s1 > 33) tod.s1 = 33;
1999/0421		if(tod.s1 > 32) tod.s1 = 32;
1999/0225		tod.multiplier = (TODFREQ<<tod.s1)/f; tod.maxdiff = 1LL<<(10 + lf);
1999/0219		iunlock(&tod); }
1999/0227/sys/src/9/port/tod.c:219,229 – 1999/0421/sys/src/9/port/tod.c:217,225
1999/0225		x = ((diff>>tod.s2)*tod.multiplier)>>(tod.s1-tod.s2);
1999/0219		x += tod.off; // protect against overflows
1999/0225		if(diff > tod.maxdiff){
1999/0219		tod.last = ticks; tod.off = x; }
1999/0421		// protect against overflows (gettod is called at least once a second) tod.last = ticks; tod.off = x;
1999/0219		/* time can't go backwards */ if(x < tod.lasttime)