1.1 --- /dev/null Thu Jan 01 00:00:00 1970 +0000
1.2 +++ b/os/persistentdata/persistentstorage/sql/SQLite/random.c Fri Jun 15 03:10:57 2012 +0200
1.3 @@ -0,0 +1,122 @@
1.4 +/*
1.5 +** 2001 September 15
1.6 +**
1.7 +** The author disclaims copyright to this source code. In place of
1.8 +** a legal notice, here is a blessing:
1.9 +**
1.10 +** May you do good and not evil.
1.11 +** May you find forgiveness for yourself and forgive others.
1.12 +** May you share freely, never taking more than you give.
1.13 +**
1.14 +*************************************************************************
1.15 +** This file contains code to implement a pseudo-random number
1.16 +** generator (PRNG) for SQLite.
1.17 +**
1.18 +** Random numbers are used by some of the database backends in order
1.19 +** to generate random integer keys for tables or random filenames.
1.20 +**
1.21 +** $Id: random.c,v 1.25 2008/06/19 01:03:18 drh Exp $
1.22 +*/
1.23 +#include "sqliteInt.h"
1.24 +
1.25 +
1.26 +/* All threads share a single random number generator.
1.27 +** This structure is the current state of the generator.
1.28 +*/
1.29 +static struct sqlite3PrngType {
1.30 + unsigned char isInit; /* True if initialized */
1.31 + unsigned char i, j; /* State variables */
1.32 + unsigned char s[256]; /* State variables */
1.33 +} sqlite3Prng;
1.34 +
1.35 +/*
1.36 +** Get a single 8-bit random value from the RC4 PRNG. The Mutex
1.37 +** must be held while executing this routine.
1.38 +**
1.39 +** Why not just use a library random generator like lrand48() for this?
1.40 +** Because the OP_NewRowid opcode in the VDBE depends on having a very
1.41 +** good source of random numbers. The lrand48() library function may
1.42 +** well be good enough. But maybe not. Or maybe lrand48() has some
1.43 +** subtle problems on some systems that could cause problems. It is hard
1.44 +** to know. To minimize the risk of problems due to bad lrand48()
1.45 +** implementations, SQLite uses this random number generator based
1.46 +** on RC4, which we know works very well.
1.47 +**
1.48 +** (Later): Actually, OP_NewRowid does not depend on a good source of
1.49 +** randomness any more. But we will leave this code in all the same.
1.50 +*/
1.51 +static int randomByte(void){
1.52 + unsigned char t;
1.53 +
1.54 +
1.55 + /* Initialize the state of the random number generator once,
1.56 + ** the first time this routine is called. The seed value does
1.57 + ** not need to contain a lot of randomness since we are not
1.58 + ** trying to do secure encryption or anything like that...
1.59 + **
1.60 + ** Nothing in this file or anywhere else in SQLite does any kind of
1.61 + ** encryption. The RC4 algorithm is being used as a PRNG (pseudo-random
1.62 + ** number generator) not as an encryption device.
1.63 + */
1.64 + if( !sqlite3Prng.isInit ){
1.65 + int i;
1.66 + char k[256];
1.67 + sqlite3Prng.j = 0;
1.68 + sqlite3Prng.i = 0;
1.69 + sqlite3OsRandomness(sqlite3_vfs_find(0), 256, k);
1.70 + for(i=0; i<256; i++){
1.71 + sqlite3Prng.s[i] = i;
1.72 + }
1.73 + for(i=0; i<256; i++){
1.74 + sqlite3Prng.j += sqlite3Prng.s[i] + k[i];
1.75 + t = sqlite3Prng.s[sqlite3Prng.j];
1.76 + sqlite3Prng.s[sqlite3Prng.j] = sqlite3Prng.s[i];
1.77 + sqlite3Prng.s[i] = t;
1.78 + }
1.79 + sqlite3Prng.isInit = 1;
1.80 + }
1.81 +
1.82 + /* Generate and return single random byte
1.83 + */
1.84 + sqlite3Prng.i++;
1.85 + t = sqlite3Prng.s[sqlite3Prng.i];
1.86 + sqlite3Prng.j += t;
1.87 + sqlite3Prng.s[sqlite3Prng.i] = sqlite3Prng.s[sqlite3Prng.j];
1.88 + sqlite3Prng.s[sqlite3Prng.j] = t;
1.89 + t += sqlite3Prng.s[sqlite3Prng.i];
1.90 + return sqlite3Prng.s[t];
1.91 +}
1.92 +
1.93 +/*
1.94 +** Return N random bytes.
1.95 +*/
1.96 +void sqlite3_randomness(int N, void *pBuf){
1.97 + unsigned char *zBuf = pBuf;
1.98 +#ifndef SQLITE_MUTEX_NOOP
1.99 + sqlite3_mutex *mutex = sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_PRNG);
1.100 +#endif
1.101 + sqlite3_mutex_enter(mutex);
1.102 + while( N-- ){
1.103 + *(zBuf++) = randomByte();
1.104 + }
1.105 + sqlite3_mutex_leave(mutex);
1.106 +}
1.107 +
1.108 +#ifndef SQLITE_OMIT_BUILTIN_TEST
1.109 +/*
1.110 +** For testing purposes, we sometimes want to preserve the state of
1.111 +** PRNG and restore the PRNG to its saved state at a later time.
1.112 +** The sqlite3_test_control() interface calls these routines to
1.113 +** control the PRNG.
1.114 +*/
1.115 +static struct sqlite3PrngType sqlite3SavedPrng;
1.116 +void sqlite3PrngSaveState(void){
1.117 + memcpy(&sqlite3SavedPrng, &sqlite3Prng, sizeof(sqlite3Prng));
1.118 +}
1.119 +void sqlite3PrngRestoreState(void){
1.120 + memcpy(&sqlite3Prng, &sqlite3SavedPrng, sizeof(sqlite3Prng));
1.121 +}
1.122 +void sqlite3PrngResetState(void){
1.123 + sqlite3Prng.isInit = 0;
1.124 +}
1.125 +#endif /* SQLITE_OMIT_BUILTIN_TEST */