File Coverage

random.c

Criterion	Covered	Total	%
statement	27	27	100.0
branch	8	8	100.0
condition			n/a
subroutine			n/a
pod			n/a
total	35	35	100.0

line	stmt	bran	code
1			/*
2			** 2001 September 15
3			**
4			** The author disclaims copyright to this source code. In place of
5			** a legal notice, here is a blessing:
6			**
7			** May you do good and not evil.
8			** May you find forgiveness for yourself and forgive others.
9			** May you share freely, never taking more than you give.
10			**
11			*************************************************************************
12			** This file contains code to implement a pseudo-random number
13			** generator (PRNG) for SQLite.
14			**
15			** Random numbers are used by some of the database backends in order
16			** to generate random integer keys for tables or random filenames.
17			**
18			** $Id: random.c,v 1.1.1.1 2004/08/08 15:03:58 matt Exp $
19			*/
20			#include "sqliteInt.h"
21			#include "os.h"
22
23
24			/*
25			** Get a single 8-bit random value from the RC4 PRNG. The Mutex
26			** must be held while executing this routine.
27			**
28			** Why not just use a library random generator like lrand48() for this?
29			** Because the OP_NewRecno opcode in the VDBE depends on having a very
30			** good source of random numbers. The lrand48() library function may
31			** well be good enough. But maybe not. Or maybe lrand48() has some
32			** subtle problems on some systems that could cause problems. It is hard
33			** to know. To minimize the risk of problems due to bad lrand48()
34			** implementations, SQLite uses this random number generator based
35			** on RC4, which we know works very well.
36			*/
37	844		static int randomByte(){
38			unsigned char t;
39
40			/* All threads share a single random number generator.
41			** This structure is the current state of the generator.
42			*/
43			static struct {
44			unsigned char isInit; /* True if initialized */
45			unsigned char i, j; /* State variables */
46			unsigned char s[256]; /* State variables */
47			} prng;
48
49			/* Initialize the state of the random number generator once,
50			** the first time this routine is called. The seed value does
51			** not need to contain a lot of randomness since we are not
52			** trying to do secure encryption or anything like that...
53			**
54			** Nothing in this file or anywhere else in SQLite does any kind of
55			** encryption. The RC4 algorithm is being used as a PRNG (pseudo-random
56			** number generator) not as an encryption device.
57			*/
58	844	100	if( !prng.isInit ){
59			int i;
60			char k[256];
61	21		prng.j = 0;
62	21		prng.i = 0;
63	21		sqliteOsRandomSeed(k);
64	5397	100	for(i=0; i<256; i++){
65	5376		prng.s[i] = i;
66			}
67	5397	100	for(i=0; i<256; i++){
68	5376		prng.j += prng.s[i] + k[i];
69	5376		t = prng.s[prng.j];
70	5376		prng.s[prng.j] = prng.s[i];
71	5376		prng.s[i] = t;
72			}
73	21		prng.isInit = 1;
74			}
75
76			/* Generate and return single random byte
77			*/
78	844		prng.i++;
79	844		t = prng.s[prng.i];
80	844		prng.j += t;
81	844		prng.s[prng.i] = prng.s[prng.j];
82	844		prng.s[prng.j] = t;
83	844		t += prng.s[prng.i];
84	844		return prng.s[t];
85			}
86
87			/*
88			** Return N random bytes.
89			*/
90	158		void sqliteRandomness(int N, void *pBuf){
91	158		unsigned char *zBuf = pBuf;
92	158		sqliteOsEnterMutex();
93	1002	100	while( N-- ){
94	844		*(zBuf++) = randomByte();
95			}
96	158		sqliteOsLeaveMutex();
97	158		}