e883f21fe8
Files correlati : sqlite Ricompilazione Demo : [ ] Commento : Passaggio da Sqlite 2 a Sqlite 3.3.5 git-svn-id: svn://10.65.10.50/trunk@13902 c028cbd2-c16b-5b4b-a496-9718f37d4682
101 lines
3.0 KiB
C
Executable File
101 lines
3.0 KiB
C
Executable File
/*
|
|
** 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 1.2 2006-04-13 12:44:29 guy Exp $
|
|
*/
|
|
#include "sqliteInt.h"
|
|
#include "os.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(){
|
|
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;
|
|
sqlite3OsRandomSeed(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 = pBuf;
|
|
sqlite3OsEnterMutex();
|
|
while( N-- ){
|
|
*(zBuf++) = randomByte();
|
|
}
|
|
sqlite3OsLeaveMutex();
|
|
}
|