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

   1 /*
   2 cpucycles/cortex.c version 20101203
   3 D. J. Bernstein
   4 Public domain.
   5 */
   6
   7 #define SCALE 1
   8 #include <time.h>
   9 #include <unistd.h>
  10 #include <sys/time.h>
  11
  12 static int enabled = 0;
  13
  14 static int prev[3];
  15 static unsigned long long prevcycles = 0;
  16 static int now[3];
  17 static long long cyclespersec = 0;
  18
  19 static void readticks(unsigned int *result)
  20 {
  21   struct timeval t;
  22   unsigned int cc;
  23   if (!enabled) {
  24     asm volatile("mcr p15, 0, %0, c9, c12, 0" :: "r"(17));
  25     asm volatile("mcr p15, 0, %0, c9, c12, 1" :: "r"(0x8000000f));
  26     asm volatile("mcr p15, 0, %0, c9, c12, 3" :: "r"(0x8000000f));
  27     enabled = 1;
  28   }
  29   asm volatile("mrc p15, 0, %0, c9, c13, 0" : "=r"(cc));
  30   gettimeofday(&t,(struct timezone *) 0);
  31   result[0] = cc;
  32   result[1] = t.tv_usec;
  33   result[2] = t.tv_sec;
  34 }
  35
  36 long long cpucycles_cortex(void)
  37 {
  38   unsigned long long delta4;
  39   int deltan;
  40   int deltas;
  41   unsigned long long guesscycles;
  42
  43   readticks(now);
  44   delta4 = (unsigned int) (now[0] - prev[0]); /* unsigned change in number of cycles mod 2^32 */
  45   deltan = now[1] - prev[1]; /* signed change in number of nanoseconds mod 10^9 */
  46   deltas = now[2] - prev[2]; /* signed change in number of seconds */
  47   if ((deltas == 0 && deltan < 200000) || (deltas == 1 && deltan < -800000))
  48     return (prevcycles + delta4) * SCALE;
  49
  50   prev[0] = now[0];
  51   prev[1] = now[1];
  52   prev[2] = now[2];
  53
  54   if ((deltas == 0 && deltan < 300000) || (deltas == 1 && deltan < -700000)) {
  55     // actual number of cycles cannot have increased by 2^32 in <0.3ms
  56     cyclespersec = 1000000 * (unsigned long long) delta4;
  57     cyclespersec /= deltan + 1000000 * (long long) deltas;
  58   } else {
  59     guesscycles = deltas * cyclespersec;
  60     guesscycles += (deltan * cyclespersec) / 1000000;
  61     while (delta4 + 2147483648ULL < guesscycles) delta4 += 4294967296ULL;
  62     /* XXX: could do longer-term extrapolation here */
  63   }
  64
  65   prevcycles += delta4;
  66   return prevcycles * SCALE;
  67 }
  68
  69 long long cpucycles_cortex_persecond(void)
  70 {
  71   while (!cyclespersec) cpucycles_cortex();
  72   return cyclespersec * SCALE;
  73 }