release/src/router/dnscrypt/src/libnacl/cpucycles/dev4ns.c

   1 #include <sys/types.h>
   2 #include <fcntl.h>
   3 #include <time.h>
   4 #include <stdio.h>
   5 #include <unistd.h>
   6 #include <sys/time.h>
   7
   8 static int fddev = -1;
   9 static int prev[3];
  10 static unsigned long long prevcycles = 0;
  11 static int now[3];
  12 static long long cyclespersec = 0;
  13
  14 static void readdev(unsigned int *result)
  15 {
  16   if (read(fddev,result,12) == 12) return;
  17   result[0] = result[1] = result[2] = 0;
  18 }
  19
  20 long long cpucycles_dev4ns(void)
  21 {
  22   unsigned long long delta4;
  23   int deltan;
  24   int deltas;
  25   unsigned long long guesscycles;
  26
  27   if (fddev == -1) {
  28     fddev = open("/dev/cpucycles4ns",O_RDONLY);
  29     readdev(prev);
  30   }
  31
  32   readdev(now);
  33   delta4 = (unsigned int) (now[0] - prev[0]); /* unsigned change in number of cycles mod 2^32 */
  34   deltan = now[1] - prev[1]; /* signed change in number of nanoseconds mod 10^9 */
  35   deltas = now[2] - prev[2]; /* signed change in number of seconds */
  36   if ((deltas == 0 && deltan < 200000000) || (deltas == 1 && deltan < -800000000))
  37     return prevcycles + delta4;
  38
  39   prev[0] = now[0];
  40   prev[1] = now[1];
  41   prev[2] = now[2];
  42
  43   if ((deltas == 0 && deltan < 300000000) || (deltas == 1 && deltan < -700000000)) {
  44     // actual number of cycles cannot have increased by 2^32 in <0.3ms
  45     cyclespersec = 1000000000 * (unsigned long long) delta4;
  46     cyclespersec /= deltan + 1000000000 * (long long) deltas;
  47   } else {
  48     guesscycles = deltas * cyclespersec;
  49     guesscycles += (deltan * cyclespersec) / 1000000000;
  50     while (delta4 + 2147483648ULL < guesscycles) delta4 += 4294967296ULL;
  51     /* XXX: could do longer-term extrapolation here */
  52   }
  53
  54   prevcycles += delta4;
  55   return prevcycles;
  56 }
  57
  58 long long cpucycles_dev4ns_persecond(void)
  59 {
  60   while (!cyclespersec) cpucycles_dev4ns();
  61   return cyclespersec;
  62 }