1 files changed, 59 insertions, 0 deletions

diff --git a/nacl/cpucycles/x86estimate.c b/nacl/cpucycles/x86estimate.c
new file mode 100644
index 00000000..e5ae66cf
--- /dev/null
+++ b/nacl/cpucycles/x86estimate.c
@@ -0,0 +1,59 @@
+#include <time.h>
+#include <sys/time.h>
+#include <sys/types.h>
+#include <sys/sysctl.h>
+
+long long cpucycles_x86estimate(void)
+{
+  long long result;
+  asm volatile(".byte 15;.byte 49" : "=A" (result));
+  return result;
+}
+
+static long long microseconds(void)
+{
+  struct timeval t;
+  gettimeofday(&t,(struct timezone *) 0);
+  return t.tv_sec * (long long) 1000000 + t.tv_usec;
+}
+
+static double guessfreq(void)
+{
+  long long tb0; long long us0;
+  long long tb1; long long us1;
+
+  tb0 = cpucycles_x86estimate();
+  us0 = microseconds();
+  do {
+    tb1 = cpucycles_x86estimate();
+    us1 = microseconds();
+  } while (us1 - us0 < 10000 || tb1 - tb0 < 1000);
+  if (tb1 <= tb0) return 0;
+  tb1 -= tb0;
+  us1 -= us0;
+  return ((double) tb1) / (0.000001 * (double) us1);
+}
+
+static double cpufrequency = 0;
+
+static void init(void)
+{
+  double guess1;
+  double guess2;
+  int loop;
+
+  for (loop = 0;loop < 100;++loop) {
+    guess1 = guessfreq();
+    guess2 = guessfreq();
+    if (guess1 > 1.01 * guess2) continue;
+    if (guess2 > 1.01 * guess1) continue;
+    cpufrequency = 0.5 * (guess1 + guess2);
+    break;
+  }
+}
+
+long long cpucycles_x86estimate_persecond(void)
+{
+  if (!cpufrequency) init();
+  return cpufrequency;
+}