/*
** 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.
*/
#include "sqliteInt.h"
/* All threads share a single random number generator.
** This structure is the current state of the generator.
*/
static SQLITE_WSD struct sqlite3PrngType {
unsigned char isInit; /* True if initialized */
unsigned char i, j; /* State variables */
unsigned char s[256]; /* State variables */
} sqlite3Prng;
/*
** 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 u8 randomByte(void){
unsigned char t;
/* The "wsdPrng" macro will resolve to the pseudo-random number generator
** state vector. If writable static data is unsupported on the target,
** we have to locate the state vector at run-time. In the more common
** case where writable static data is supported, wsdPrng can refer directly
** to the "sqlite3Prng" state vector declared above.
*/
#ifdef SQLITE_OMIT_WSD
struct sqlite3PrngType *p = &GLOBAL(struct sqlite3PrngType, sqlite3Prng);
# define wsdPrng p[0]
#else
# define wsdPrng sqlite3Prng
#endif
/* 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( !wsdPrng.isInit ){
int i;
char k[256];
wsdPrng.j = 0;
wsdPrng.i = 0;
sqlite3OsRandomness(sqlite3_vfs_find(0), 256, k);
for(i=0; i<256; i++){
wsdPrng.s[i] = (u8)i;
}
for(i=0; i<256; i++){
wsdPrng.j += wsdPrng.s[i] + k[i];
t = wsdPrng.s[wsdPrng.j];
wsdPrng.s[wsdPrng.j] = wsdPrng.s[i];
wsdPrng.s[i] = t;
}
wsdPrng.isInit = 1;
}
/* Generate and return single random byte
*/
wsdPrng.i++;
t = wsdPrng.s[wsdPrng.i];
wsdPrng.j += t;
wsdPrng.s[wsdPrng.i] = wsdPrng.s[wsdPrng.j];
wsdPrng.s[wsdPrng.j] = t;
t += wsdPrng.s[wsdPrng.i];
return wsdPrng.s[t];
}
/*
** Return N random bytes.
*/
void sqlite3_randomness(int N, void *pBuf){
unsigned char *zBuf = pBuf;
#if SQLITE_THREADSAFE
sqlite3_mutex *mutex = sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_PRNG);
#endif
sqlite3_mutex_enter(mutex);
while( N-- ){
*(zBuf++) = randomByte();
}
sqlite3_mutex_leave(mutex);
}
#ifndef SQLITE_OMIT_BUILTIN_TEST
/*
** For testing purposes, we sometimes want to preserve the state of
** PRNG and restore the PRNG to its saved state at a later time, or
** to reset the PRNG to its initial state. These routines accomplish
** those tasks.
**
** The sqlite3_test_control() interface calls these routines to
** control the PRNG.
*/
static SQLITE_WSD struct sqlite3PrngType sqlite3SavedPrng;
void sqlite3PrngSaveState(void){
memcpy(
&GLOBAL(struct sqlite3PrngType, sqlite3SavedPrng),
&GLOBAL(struct sqlite3PrngType, sqlite3Prng),
sizeof(sqlite3Prng)
);
}
void sqlite3PrngRestoreState(void){
memcpy(
&GLOBAL(struct sqlite3PrngType, sqlite3Prng),
&GLOBAL(struct sqlite3PrngType, sqlite3SavedPrng),
sizeof(sqlite3Prng)
);
}
void sqlite3PrngResetState(void){
GLOBAL(struct sqlite3PrngType, sqlite3Prng).isInit = 0;
}
#endif /* SQLITE_OMIT_BUILTIN_TEST */