/*
** 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.c,v 1.7 2001/09/23 19:46:52 drh Exp $
*/
#include "sqliteInt.h"
#include "os.h"
/*
** Get a single 8-bit random value from the RC4 PRNG.
*/
int sqliteRandomByte(sqlite *db){
int t;
/* 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( !db->prng.isInit ){
int i;
char k[256];
db->prng.j = 0;
db->prng.i = 0;
sqliteOsRandomSeed(k);
for(i=0; i<256; i++){
db->prng.s[i] = i;
}
for(i=0; i<256; i++){
int t;
db->prng.j = (db->prng.j + db->prng.s[i] + k[i]) & 0xff;
t = db->prng.s[db->prng.j];
db->prng.s[db->prng.j] = db->prng.s[i];
db->prng.s[i] = t;
}
db->prng.isInit = 1;
}
/* Generate and return single random byte
*/
db->prng.i = (db->prng.i + 1) & 0xff;
db->prng.j = (db->prng.j + db->prng.s[db->prng.i]) & 0xff;
t = db->prng.s[db->prng.i];
db->prng.s[db->prng.i] = db->prng.s[db->prng.j];
db->prng.s[db->prng.j] = t;
t = db->prng.s[db->prng.i] + db->prng.s[db->prng.j];
return db->prng.s[t & 0xff];
}
/*
** Return a random 32-bit integer. The integer is generated by making
** 4 calls to sqliteRandomByte().
*/
int sqliteRandomInteger(sqlite *db){
int r;
int i;
r = sqliteRandomByte(db);
for(i=1; i<4; i++){
r = (r<<8) + sqliteRandomByte(db);
}
return r;
}