--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/engine/sqlite/src/random.cpp	Thu Feb 25 14:29:19 2010 +0000
@@ -0,0 +1,103 @@
+/*
+** 2001 September 15
+**
+** The author disclaims copyright to this source code.  In place of
+** a legal notice, here is a blessing:
+**
+**    May you do good and not evil.
+**    May you find forgiveness for yourself and forgive others.
+**    May you share freely, never taking more than you give.
+**
+*************************************************************************
+** This file contains code to implement a pseudo-random number
+** generator (PRNG) for SQLite.
+**
+** Random numbers are used by some of the database backends in order
+** to generate random integer keys for tables or random filenames.
+**
+** $Id: random.cpp 1282 2008-11-13 09:31:33Z LarsPson $
+*/
+#include "sqliteInt.h"
+
+
+/*
+** Get a single 8-bit random value from the RC4 PRNG.  The Mutex
+** must be held while executing this routine.
+**
+** Why not just use a library random generator like lrand48() for this?
+** Because the OP_NewRowid opcode in the VDBE depends on having a very
+** good source of random numbers.  The lrand48() library function may
+** well be good enough.  But maybe not.  Or maybe lrand48() has some
+** subtle problems on some systems that could cause problems.  It is hard
+** to know.  To minimize the risk of problems due to bad lrand48()
+** implementations, SQLite uses this random number generator based
+** on RC4, which we know works very well.
+**
+** (Later):  Actually, OP_NewRowid does not depend on a good source of
+** randomness any more.  But we will leave this code in all the same.
+*/
+static int randomByte(void){
+  unsigned char t;
+
+  /* All threads share a single random number generator.
+  ** This structure is the current state of the generator.
+  */
+  static struct {
+    unsigned char isInit;          /* True if initialized */
+    unsigned char i, j;            /* State variables */
+    unsigned char s[256];          /* State variables */
+  } prng;
+
+  /* Initialize the state of the random number generator once,
+  ** the first time this routine is called.  The seed value does
+  ** not need to contain a lot of randomness since we are not
+  ** trying to do secure encryption or anything like that...
+  **
+  ** Nothing in this file or anywhere else in SQLite does any kind of
+  ** encryption.  The RC4 algorithm is being used as a PRNG (pseudo-random
+  ** number generator) not as an encryption device.
+  */
+  if( !prng.isInit ){
+    int i;
+    char k[256];
+    prng.j = 0;
+    prng.i = 0;
+    sqlite3OsRandomness(sqlite3_vfs_find(0), 256, k);
+    for(i=0; i<256; i++){
+      prng.s[i] = i;
+    }
+    for(i=0; i<256; i++){
+      prng.j += prng.s[i] + k[i];
+      t = prng.s[prng.j];
+      prng.s[prng.j] = prng.s[i];
+      prng.s[i] = t;
+    }
+    prng.isInit = 1;
+  }
+
+  /* Generate and return single random byte
+  */
+  prng.i++;
+  t = prng.s[prng.i];
+  prng.j += t;
+  prng.s[prng.i] = prng.s[prng.j];
+  prng.s[prng.j] = t;
+  t += prng.s[prng.i];
+  return prng.s[t];
+}
+
+/*
+** Return N random bytes.
+*/
+void sqlite3Randomness(int N, void *pBuf){
+  unsigned char *zBuf = (unsigned char*)pBuf;
+  static sqlite3_mutex *mutex = 0;
+  if( mutex==0 ){
+    mutex = sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_PRNG);
+  }
+  sqlite3_mutex_enter(mutex);
+  while( N-- ){
+    *(zBuf++) = randomByte();
+  }
+  sqlite3_mutex_leave(mutex);
+}