Initial Commit

.svn/pristine/0a/0a1822ebb4debbfdc5bf05419628fddf99e84070.svn-base

@@ -0,0 +1,82 @@
+#include "init_random_seed.h"
+
+#include <stdlib.h>
+#include <stdint.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <sys/time.h>
+#include <unistd.h>
+
+/* basic PRNG to use for improving the basic seed selection */
+static unsigned lcg (uint64_t seed)
+{
+  if (0 ==seed)
+    {
+      seed = UINT64_C(104729);
+    }
+  else
+    {
+      seed %= UINT64_C(4294967296);
+    }
+  seed = (seed * UINT64_C(279470273)) % UINT64_C(4294967291);
+  return seed % UINT64_MAX;
+}
+
+/* Generate a good PRNG seed value */
+void init_random_seed(void)
+{
+  unsigned seed = 0u;
+  int have_seed = 0;
+
+  // try /dev/urandom for an initial seed
+  int random_source;
+  if ((random_source = open ("/dev/urandom", O_RDONLY)) >= 0)
+    {
+      size_t random_data_length = 0;
+      have_seed = -1;
+      while (random_data_length < sizeof seed)
+        {
+          ssize_t result = read (random_source, &seed + random_data_length, (sizeof seed) - random_data_length);
+          if (result < 0)
+            {
+              // error, unable to read /dev/random
+              have_seed = 0;
+            }
+          random_data_length += result;
+        }
+      close (random_source);
+    }
+  if (!have_seed)
+    {
+      // fallback to combining the time and PID in a fairly random way
+      pid_t pid = getpid ();
+      struct timeval tv;
+      gettimeofday (&tv, NULL);
+      seed = (unsigned)(((unsigned)pid << 16)
+        ^ (unsigned)pid
+        ^ (unsigned)tv.tv_sec
+        ^ (unsigned)tv.tv_usec);
+      seed = lcg (seed);
+    }
+  srand (seed);
+}
+
+#ifdef TEST
+#include <stdio.h>
+
+int main (int argc, char * argv[])
+{
+  init_random_seed ();
+  int i, j;
+  int r[10][4];
+  for (i = 0; i < 10; ++i)
+    {
+      for (j = 0; j < 4; ++j)
+        {
+          printf ("%10d ", rand ());
+        }
+      printf ("\n");
+    }
+  return 0;
+}
+#endif