mirror of
https://github.com/servalproject/serval-dna.git
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63 lines
1.7 KiB
C
63 lines
1.7 KiB
C
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#include <sys/types.h>
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#include <fcntl.h>
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#include <time.h>
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#include <stdio.h>
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#include <unistd.h>
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#include <sys/time.h>
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static int fddev = -1;
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static int prev[3];
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static unsigned long long prevcycles = 0;
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static int now[3];
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static long long cyclespersec = 0;
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static void readdev(unsigned int *result)
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{
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if (read(fddev,result,12) == 12) return;
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result[0] = result[1] = result[2] = 0;
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}
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long long cpucycles_dev4ns(void)
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{
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unsigned long long delta4;
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int deltan;
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int deltas;
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unsigned long long guesscycles;
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if (fddev == -1) {
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fddev = open("/dev/cpucycles4ns",O_RDONLY);
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readdev(prev);
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}
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readdev(now);
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delta4 = (unsigned int) (now[0] - prev[0]); /* unsigned change in number of cycles mod 2^32 */
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deltan = now[1] - prev[1]; /* signed change in number of nanoseconds mod 10^9 */
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deltas = now[2] - prev[2]; /* signed change in number of seconds */
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if ((deltas == 0 && deltan < 200000000) || (deltas == 1 && deltan < -800000000))
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return prevcycles + delta4;
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prev[0] = now[0];
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prev[1] = now[1];
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prev[2] = now[2];
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if ((deltas == 0 && deltan < 300000000) || (deltas == 1 && deltan < -700000000)) {
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// actual number of cycles cannot have increased by 2^32 in <0.3ms
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cyclespersec = 1000000000 * (unsigned long long) delta4;
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cyclespersec /= deltan + 1000000000 * (long long) deltas;
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} else {
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guesscycles = deltas * cyclespersec;
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guesscycles += (deltan * cyclespersec) / 1000000000;
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while (delta4 + 2147483648ULL < guesscycles) delta4 += 4294967296ULL;
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/* XXX: could do longer-term extrapolation here */
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}
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prevcycles += delta4;
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return prevcycles;
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}
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long long cpucycles_dev4ns_persecond(void)
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{
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while (!cyclespersec) cpucycles_dev4ns();
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return cyclespersec;
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}
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