1 files changed, 127 insertions, 0 deletions
diff --git a/src/random.c b/src/random.c
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+++ b/src/random.c
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+/*
+** Copyright (c) 2000 D. Richard Hipp
+**
+** This program is free software; you can redistribute it and/or
+** modify it under the terms of the GNU General Public
+** License as published by the Free Software Foundation; either
+** version 2 of the License, or (at your option) any later version.
+**
+** This program is distributed in the hope that it will be useful,
+** but WITHOUT ANY WARRANTY; without even the implied warranty of
+** MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+** General Public License for more details.
+** 
+** You should have received a copy of the GNU General Public
+** License along with this library; if not, write to the
+** Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+** Boston, MA  02111-1307, USA.
+**
+** Author contact information:
+**   drh@hwaci.com
+**   http://www.hwaci.com/drh/
+**
+*************************************************************************
+** 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.c,v 1.1 2001/01/13 14:34:07 drh Exp $
+*/
+#include "sqliteInt.h"
+
+
+/*
+** Get a single 8-bit random value from the RC4 PRNG.
+*/
+int sqliteRandomByte(void){
+  int t;
+
+  /*
+  ** The following structure holds the current state of the RC4 algorithm.
+  ** We use RC4 as a random number generator.  Each call to RC4 gives
+  ** a random 8-bit number.
+  **
+  ** 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.
+  */
+  static struct {
+    int isInit;
+    int i, j;
+    int s[256];
+  } prng_state;
+ 
+  /* 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...
+  */
+  if( !prng_state.isInit ){
+    int i;
+    static char seed[] = "    sqlite random seed";
+    char k[256];
+    time((time_t*)seed);
+    prng_state.j = 0;
+    prng_state.i = 0;
+    for(i=0; i<256; i++){
+      prng_state.s[i] = i;
+      k[i] = seed[i%sizeof(seed)];
+    }
+    for(i=0; i<256; i++){
+      int t;
+      prng_state.j = (prng_state.j + prng_state.s[i] + k[i]) & 0xff;
+      t = prng_state.s[prng_state.j];
+      prng_state.s[prng_state.j] = prng_state.s[i];
+      prng_state.s[i] = t;
+    }
+    prng_state.isInit = 1;
+  }
+
+  /* Generate and return single random byte
+  */
+  prng_state.i = (prng_state.i + 1) & 0xff;
+  prng_state.j = (prng_state.j + prng_state.s[prng_state.i]) & 0xff;
+  t = prng_state.s[prng_state.i];
+  prng_state.s[prng_state.i] = prng_state.s[prng_state.j];
+  prng_state.s[prng_state.j] = t;
+  t = prng_state.s[prng_state.i] + prng_state.s[prng_state.j];
+  return t & 0xff;
+}
+
+/*
+** Return a random 32-bit integer.  The integer is generated by making
+** 4 calls to sqliteRandomByte().
+*/
+int sqliteRandomInteger(void){
+  int r;
+  int i;
+  r = sqliteRandomByte();
+  for(i=1; i<4; i++){
+    r = (r<<8) + sqliteRandomByte();
+  }
+  return r;
+}
+
+
+/*
+** Generate a random filename with the given prefix.  The new filename
+** is written into zBuf[].  The calling function must insure that
+** zBuf[] is big enough to hold the prefix plus 20 or so extra
+** characters.
+**
+** Very random names are chosen so that the chance of a
+** collision with an existing filename is very very small.
+*/
+void sqliteRandomName(char *zBuf, char *zPrefix){
+  int i, j;
+  static const char zRandomChars[] = "abcdefghijklmnopqrstuvwxyz0123456789";
+  strcpy(zBuf, zPrefix);
+  j = strlen(zBuf);
+  for(i=0; i<15; i++){
+    int c = sqliteRandomByte() % (sizeof(zRandomChars) - 1);
+    zBuf[j++] = zRandomChars[c];
+  }
+  zBuf[j] = 0;
+}