1 files changed, 62 insertions, 0 deletions

diff --git a/nacl/cpucycles/dev4ns.c b/nacl/cpucycles/dev4ns.c
new file mode 100644
index 00000000..73ff5755
--- /dev/null
+++ b/nacl/cpucycles/dev4ns.c
@@ -0,0 +1,62 @@
+#include <sys/types.h>
+#include <fcntl.h>
+#include <time.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <sys/time.h>
+
+static int fddev = -1;
+static int prev[3];
+static unsigned long long prevcycles = 0;
+static int now[3];
+static long long cyclespersec = 0;
+
+static void readdev(unsigned int *result)
+{
+  if (read(fddev,result,12) == 12) return;
+  result[0] = result[1] = result[2] = 0;
+}
+
+long long cpucycles_dev4ns(void)
+{
+  unsigned long long delta4;
+  int deltan;
+  int deltas;
+  unsigned long long guesscycles;
+
+  if (fddev == -1) {
+    fddev = open("/dev/cpucycles4ns",O_RDONLY);
+    readdev(prev);
+  }
+  
+  readdev(now);
+  delta4 = (unsigned int) (now[0] - prev[0]); /* unsigned change in number of cycles mod 2^32 */
+  deltan = now[1] - prev[1]; /* signed change in number of nanoseconds mod 10^9 */
+  deltas = now[2] - prev[2]; /* signed change in number of seconds */
+  if ((deltas == 0 && deltan < 200000000) || (deltas == 1 && deltan < -800000000))
+    return prevcycles + delta4;
+
+  prev[0] = now[0];
+  prev[1] = now[1];
+  prev[2] = now[2];
+
+  if ((deltas == 0 && deltan < 300000000) || (deltas == 1 && deltan < -700000000)) {
+    // actual number of cycles cannot have increased by 2^32 in <0.3ms
+    cyclespersec = 1000000000 * (unsigned long long) delta4;
+    cyclespersec /= deltan + 1000000000 * (long long) deltas;
+  } else {
+    guesscycles = deltas * cyclespersec;
+    guesscycles += (deltan * cyclespersec) / 1000000000;
+    while (delta4 + 2147483648ULL < guesscycles) delta4 += 4294967296ULL;
+    /* XXX: could do longer-term extrapolation here */
+  }
+
+  prevcycles += delta4;
+  return prevcycles;
+}
+
+long long cpucycles_dev4ns_persecond(void)
+{
+  while (!cyclespersec) cpucycles_dev4ns();
+  return cyclespersec;
+}