1 files changed, 73 insertions, 0 deletions

diff --git a/nacl/cpucycles/cortex.c b/nacl/cpucycles/cortex.c
new file mode 100644
index 00000000..07e2fa02
--- /dev/null
+++ b/nacl/cpucycles/cortex.c
@@ -0,0 +1,73 @@
+/*
+cpucycles/cortex.c version 20101203
+D. J. Bernstein
+Public domain.
+*/
+
+#define SCALE 1
+#include <time.h>
+#include <unistd.h>
+#include <sys/time.h>
+
+static int enabled = 0;
+
+static int prev[3];
+static unsigned long long prevcycles = 0;
+static int now[3];
+static long long cyclespersec = 0;
+
+static void readticks(unsigned int *result)
+{
+  struct timeval t;
+  unsigned int cc;
+  if (!enabled) {
+    asm volatile("mcr p15, 0, %0, c9, c12, 0" :: "r"(17));
+    asm volatile("mcr p15, 0, %0, c9, c12, 1" :: "r"(0x8000000f));
+    asm volatile("mcr p15, 0, %0, c9, c12, 3" :: "r"(0x8000000f));
+    enabled = 1;
+  }
+  asm volatile("mrc p15, 0, %0, c9, c13, 0" : "=r"(cc));
+  gettimeofday(&t,(struct timezone *) 0);
+  result[0] = cc;
+  result[1] = t.tv_usec;
+  result[2] = t.tv_sec;
+}
+
+long long cpucycles_cortex(void)
+{
+  unsigned long long delta4;
+  int deltan;
+  int deltas;
+  unsigned long long guesscycles;
+  
+  readticks(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 < 200000) || (deltas == 1 && deltan < -800000))
+    return (prevcycles + delta4) * SCALE;
+
+  prev[0] = now[0];
+  prev[1] = now[1];
+  prev[2] = now[2];
+
+  if ((deltas == 0 && deltan < 300000) || (deltas == 1 && deltan < -700000)) {
+    // actual number of cycles cannot have increased by 2^32 in <0.3ms
+    cyclespersec = 1000000 * (unsigned long long) delta4;
+    cyclespersec /= deltan + 1000000 * (long long) deltas;
+  } else {
+    guesscycles = deltas * cyclespersec;
+    guesscycles += (deltan * cyclespersec) / 1000000;
+    while (delta4 + 2147483648ULL < guesscycles) delta4 += 4294967296ULL;
+    /* XXX: could do longer-term extrapolation here */
+  }
+
+  prevcycles += delta4;
+  return prevcycles * SCALE;
+}
+
+long long cpucycles_cortex_persecond(void)
+{
+  while (!cyclespersec) cpucycles_cortex();
+  return cyclespersec * SCALE;
+}