123 lines
3.7 KiB
C
123 lines
3.7 KiB
C
/*
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** 2001 September 15
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**
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** The author disclaims copyright to this source code. In place of
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** a legal notice, here is a blessing:
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**
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** May you do good and not evil.
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** May you find forgiveness for yourself and forgive others.
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** May you share freely, never taking more than you give.
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**
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*************************************************************************
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** This file contains code to implement a pseudo-random number
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** generator (PRNG) for SQLite.
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**
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** Random numbers are used by some of the database backends in order
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** to generate random integer keys for tables or random filenames.
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*/
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#include "sqliteInt.h"
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/* All threads share a single random number generator.
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** This structure is the current state of the generator.
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*/
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static SQLITE_WSD struct sqlite3PrngType {
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unsigned char isInit; /* True if initialized */
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unsigned char i, j; /* State variables */
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unsigned char s[256]; /* State variables */
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} sqlite3Prng;
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/*
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** Return N random bytes.
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*/
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void sqlite3_randomness(int N, void *pBuf){
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unsigned char t;
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unsigned char *zBuf = pBuf;
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/* The "wsdPrng" macro will resolve to the pseudo-random number generator
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** state vector. If writable static data is unsupported on the target,
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** we have to locate the state vector at run-time. In the more common
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** case where writable static data is supported, wsdPrng can refer directly
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** to the "sqlite3Prng" state vector declared above.
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*/
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#ifdef SQLITE_OMIT_WSD
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struct sqlite3PrngType *p = &GLOBAL(struct sqlite3PrngType, sqlite3Prng);
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# define wsdPrng p[0]
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#else
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# define wsdPrng sqlite3Prng
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#endif
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#if SQLITE_THREADSAFE
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sqlite3_mutex *mutex = sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_PRNG);
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sqlite3_mutex_enter(mutex);
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#endif
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/* Initialize the state of the random number generator once,
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** the first time this routine is called. The seed value does
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** not need to contain a lot of randomness since we are not
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** trying to do secure encryption or anything like that...
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**
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** Nothing in this file or anywhere else in SQLite does any kind of
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** encryption. The RC4 algorithm is being used as a PRNG (pseudo-random
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** number generator) not as an encryption device.
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*/
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if( !wsdPrng.isInit ){
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int i;
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char k[256];
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wsdPrng.j = 0;
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wsdPrng.i = 0;
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sqlite3OsRandomness(sqlite3_vfs_find(0), 256, k);
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for(i=0; i<256; i++){
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wsdPrng.s[i] = (u8)i;
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}
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for(i=0; i<256; i++){
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wsdPrng.j += wsdPrng.s[i] + k[i];
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t = wsdPrng.s[wsdPrng.j];
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wsdPrng.s[wsdPrng.j] = wsdPrng.s[i];
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wsdPrng.s[i] = t;
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}
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wsdPrng.isInit = 1;
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}
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while( N-- ){
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wsdPrng.i++;
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t = wsdPrng.s[wsdPrng.i];
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wsdPrng.j += t;
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wsdPrng.s[wsdPrng.i] = wsdPrng.s[wsdPrng.j];
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wsdPrng.s[wsdPrng.j] = t;
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t += wsdPrng.s[wsdPrng.i];
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*(zBuf++) = wsdPrng.s[t];
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}
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sqlite3_mutex_leave(mutex);
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}
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#ifndef SQLITE_OMIT_BUILTIN_TEST
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/*
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** For testing purposes, we sometimes want to preserve the state of
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** PRNG and restore the PRNG to its saved state at a later time, or
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** to reset the PRNG to its initial state. These routines accomplish
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** those tasks.
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**
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** The sqlite3_test_control() interface calls these routines to
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** control the PRNG.
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*/
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static SQLITE_WSD struct sqlite3PrngType sqlite3SavedPrng;
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void sqlite3PrngSaveState(void){
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memcpy(
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&GLOBAL(struct sqlite3PrngType, sqlite3SavedPrng),
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&GLOBAL(struct sqlite3PrngType, sqlite3Prng),
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sizeof(sqlite3Prng)
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);
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}
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void sqlite3PrngRestoreState(void){
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memcpy(
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&GLOBAL(struct sqlite3PrngType, sqlite3Prng),
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&GLOBAL(struct sqlite3PrngType, sqlite3SavedPrng),
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sizeof(sqlite3Prng)
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);
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}
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void sqlite3PrngResetState(void){
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GLOBAL(struct sqlite3PrngType, sqlite3Prng).isInit = 0;
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}
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#endif /* SQLITE_OMIT_BUILTIN_TEST */
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