release/src/router/dnscrypt/src/libnacl/cpucycles/x86estimate.c

   1 #include <time.h>
   2 #include <sys/time.h>
   3 #include <sys/types.h>
   4 #include <sys/param.h>
   5 #include <sys/sysctl.h>
   6
   7 long long cpucycles_x86estimate(void)
   8 {
   9   long long result;
  10   asm volatile(".byte 15;.byte 49" : "=A" (result));
  11   return result;
  12 }
  13
  14 static long long microseconds(void)
  15 {
  16   struct timeval t;
  17   gettimeofday(&t,(struct timezone *) 0);
  18   return t.tv_sec * (long long) 1000000 + t.tv_usec;
  19 }
  20
  21 static double guessfreq(void)
  22 {
  23   long long tb0; long long us0;
  24   long long tb1; long long us1;
  25
  26   tb0 = cpucycles_x86estimate();
  27   us0 = microseconds();
  28   do {
  29     tb1 = cpucycles_x86estimate();
  30     us1 = microseconds();
  31   } while (us1 - us0 < 10000 || tb1 - tb0 < 1000);
  32   if (tb1 <= tb0) return 0;
  33   tb1 -= tb0;
  34   us1 -= us0;
  35   return ((double) tb1) / (0.000001 * (double) us1);
  36 }
  37
  38 static double cpufrequency = 0;
  39
  40 static void init(void)
  41 {
  42   double guess1;
  43   double guess2;
  44   int loop;
  45
  46   for (loop = 0;loop < 100;++loop) {
  47     guess1 = guessfreq();
  48     guess2 = guessfreq();
  49     if (guess1 > 1.01 * guess2) continue;
  50     if (guess2 > 1.01 * guess1) continue;
  51     cpufrequency = 0.5 * (guess1 + guess2);
  52     break;
  53   }
  54 }
  55
  56 long long cpucycles_x86estimate_persecond(void)
  57 {
  58   if (!cpufrequency) init();
  59   return cpufrequency;
  60 }