1 /* Pseudo random number generation functions derived from the drand48()
2 * function obtained from pysam source code.
3 *
4 * This functions are used in order to replace the default math.random()
5 * Lua implementation with something having exactly the same behavior
6 * across different systems (by default Lua uses libc's rand() that is not
7 * required to implement a specific PRNG generating the same sequence
8 * in different systems if seeded with the same integer).
9 *
10 * The original code appears to be under the public domain.
11 * I modified it removing the non needed functions and all the
12 * 1960-style C coding stuff...
13 *
14 * ----------------------------------------------------------------------------
15 *
16 * Copyright (c) 2010-2012, Salvatore Sanfilippo <antirez at gmail dot com>
17 * All rights reserved.
18 *
19 * Redistribution and use in source and binary forms, with or without
20 * modification, are permitted provided that the following conditions are met:
21 *
22 * * Redistributions of source code must retain the above copyright notice,
23 * this list of conditions and the following disclaimer.
24 * * Redistributions in binary form must reproduce the above copyright
25 * notice, this list of conditions and the following disclaimer in the
26 * documentation and/or other materials provided with the distribution.
27 * * Neither the name of Redis nor the names of its contributors may be used
28 * to endorse or promote products derived from this software without
29 * specific prior written permission.
30 *
31 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
32 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
33 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
34 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
35 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
36 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
37 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
38 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
39 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
40 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
41 * POSSIBILITY OF SUCH DAMAGE.
42 */
43
44 #include <stdint.h>
45
46 #define N 16
47 #define MASK ((1 << (N - 1)) + (1 << (N - 1)) - 1)
48 #define LOW(x) ((unsigned)(x) & MASK)
49 #define HIGH(x) LOW((x) >> N)
50 #define MUL(x, y, z) { int32_t l = (long)(x) * (long)(y); \
51 (z)[0] = LOW(l); (z)[1] = HIGH(l); }
52 #define CARRY(x, y) ((int32_t)(x) + (long)(y) > MASK)
53 #define ADDEQU(x, y, z) (z = CARRY(x, (y)), x = LOW(x + (y)))
54 #define X0 0x330E
55 #define X1 0xABCD
56 #define X2 0x1234
57 #define A0 0xE66D
58 #define A1 0xDEEC
59 #define A2 0x5
60 #define C 0xB
61 #define SET3(x, x0, x1, x2) ((x)[0] = (x0), (x)[1] = (x1), (x)[2] = (x2))
62 #define SETLOW(x, y, n) SET3(x, LOW((y)[n]), LOW((y)[(n)+1]), LOW((y)[(n)+2]))
63 #define SEED(x0, x1, x2) (SET3(x, x0, x1, x2), SET3(a, A0, A1, A2), c = C)
64 #define REST(v) for (i = 0; i < 3; i++) { xsubi[i] = x[i]; x[i] = temp[i]; } \
65 return (v);
66 #define HI_BIT (1L << (2 * N - 1))
67
68 static uint32_t x[3] = { X0, X1, X2 }, a[3] = { A0, A1, A2 }, c = C;
69 static void next(void);
70
redisLrand48()71 int32_t redisLrand48() {
72 next();
73 return (((int32_t)x[2] << (N - 1)) + (x[1] >> 1));
74 }
75
redisSrand48(int32_t seedval)76 void redisSrand48(int32_t seedval) {
77 SEED(X0, LOW(seedval), HIGH(seedval));
78 }
79
next(void)80 static void next(void) {
81 uint32_t p[2], q[2], r[2], carry0, carry1;
82
83 MUL(a[0], x[0], p);
84 ADDEQU(p[0], c, carry0);
85 ADDEQU(p[1], carry0, carry1);
86 MUL(a[0], x[1], q);
87 ADDEQU(p[1], q[0], carry0);
88 MUL(a[1], x[0], r);
89 x[2] = LOW(carry0 + carry1 + CARRY(p[1], r[0]) + q[1] + r[1] +
90 a[0] * x[2] + a[1] * x[1] + a[2] * x[0]);
91 x[1] = LOW(p[1] + r[0]);
92 x[0] = LOW(p[0]);
93 }
94