drh
104 lines
2.6 KiB
C
104 lines
2.6 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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** $Id: random.c,v 1.8 2001/10/09 04:19:47 drh Exp $
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*/
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#include "sqliteInt.h"
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#include "os.h"
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/*
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** Get a single 8-bit random value from the RC4 PRNG. The Mutex
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** must be held while executing this routine.
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*/
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static int randomByte(){
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int t;
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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 struct {
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int isInit; /* True if initialized */
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int i, j; /* State variables */
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int s[256]; /* State variables */
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} prng;
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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( !prng.isInit ){
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int i;
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char k[256];
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prng.j = 0;
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prng.i = 0;
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sqliteOsRandomSeed(k);
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for(i=0; i<256; i++){
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prng.s[i] = i;
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}
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for(i=0; i<256; i++){
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int t;
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prng.j = (prng.j + prng.s[i] + k[i]) & 0xff;
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t = prng.s[prng.j];
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prng.s[prng.j] = prng.s[i];
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prng.s[i] = t;
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}
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prng.isInit = 1;
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}
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/* Generate and return single random byte
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*/
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prng.i = (prng.i + 1) & 0xff;
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prng.j = (prng.j + prng.s[prng.i]) & 0xff;
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t = prng.s[prng.i];
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prng.s[prng.i] = prng.s[prng.j];
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prng.s[prng.j] = t;
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t = prng.s[prng.i] + prng.s[prng.j];
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return prng.s[t & 0xff];
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}
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/*
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** Return an random 8-bit integer.
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*/
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int sqliteRandomByte(){
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int r;
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sqliteOsEnterMutex();
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r = randomByte();
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sqliteOsLeaveMutex();
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return r;
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}
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/*
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** Return a random 32-bit integer. The integer is generated by making
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** 4 calls to sqliteRandomByte().
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*/
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int sqliteRandomInteger(){
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int r;
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int i;
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sqliteOsEnterMutex();
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r = randomByte();
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for(i=1; i<4; i++){
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r = (r<<8) + randomByte();
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}
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sqliteOsLeaveMutex();
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return r;
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}
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