1/*
2 * Copyright © 2012 Siarhei Siamashka <siarhei.siamashka@gmail.com>
3 *
4 * Based on the public domain implementation of small noncryptographic PRNG
5 * authored by Bob Jenkins: http://burtleburtle.net/bob/rand/smallprng.html
6 *
7 * Permission is hereby granted, free of charge, to any person obtaining a
8 * copy of this software and associated documentation files (the "Software"),
9 * to deal in the Software without restriction, including without limitation
10 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
11 * and/or sell copies of the Software, and to permit persons to whom the
12 * Software is furnished to do so, subject to the following conditions:
13 *
14 * The above copyright notice and this permission notice (including the next
15 * paragraph) shall be included in all copies or substantial portions of the
16 * Software.
17 *
18 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
19 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
20 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
21 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
22 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
23 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
24 * DEALINGS IN THE SOFTWARE.
25 */
26
27#ifndef __UTILS_PRNG_H__
28#define __UTILS_PRNG_H__
29
30/*
31 * This file provides a fast SIMD-optimized noncryptographic PRNG (pseudorandom
32 * number generator), with the output good enough to pass "Big Crush" tests
33 * from TestU01 (http://en.wikipedia.org/wiki/TestU01).
34 *
35 * SIMD code uses http://gcc.gnu.org/onlinedocs/gcc/Vector-Extensions.html
36 * which is a GCC specific extension. There is also a slower alternative
37 * code path, which should work with any C compiler.
38 *
39 * The "prng_t" structure keeps the internal state of the random number
40 * generator. It is possible to have multiple instances of the random number
41 * generator active at the same time, in this case each of them needs to have
42 * its own "prng_t". All the functions take a pointer to "prng_t"
43 * as the first argument.
44 *
45 * Functions:
46 *
47 * ----------------------------------------------------------------------------
48 * void prng_srand_r (prng_t *prng, uint32_t seed);
49 *
50 * Initialize the pseudorandom number generator. The sequence of preudorandom
51 * numbers is deterministic and only depends on "seed". Any two generators
52 * initialized with the same seed will produce exactly the same sequence.
53 *
54 * ----------------------------------------------------------------------------
55 * uint32_t prng_rand_r (prng_t *prng);
56 *
57 * Generate a single uniformly distributed 32-bit pseudorandom value.
58 *
59 * ----------------------------------------------------------------------------
60 * void prng_randmemset_r (prng_t                  *prng,
61 *                         void                    *buffer,
62 *                         size_t                   size,
63 *                         prng_randmemset_flags_t  flags);
64 *
65 * Fills the memory buffer "buffer" with "size" bytes of pseudorandom data.
66 * The "flags" argument may be used to tweak some statistics properties:
67 *    RANDMEMSET_MORE_00 - set ~25% of bytes to 0x00
68 *    RANDMEMSET_MORE_FF - set ~25% of bytes to 0xFF
69 * The flags can be combined. This allows a bit better simulation of typical
70 * pixel data, which normally contains a lot of fully transparent or fully
71 * opaque pixels.
72 */
73
74#ifdef HAVE_CONFIG_H
75#include <pixman-config.h>
76#endif
77
78#include "pixman-private.h"
79
80/*****************************************************************************/
81
82#ifdef HAVE_GCC_VECTOR_EXTENSIONS
83typedef uint32_t uint32x4 __attribute__ ((vector_size(16)));
84typedef uint8_t  uint8x16 __attribute__ ((vector_size(16)));
85#endif
86
87typedef struct
88{
89    uint32_t a, b, c, d;
90} smallprng_t;
91
92typedef struct
93{
94#ifdef HAVE_GCC_VECTOR_EXTENSIONS
95    uint32x4 a, b, c, d;
96#else
97    smallprng_t p1, p2, p3, p4;
98#endif
99    smallprng_t p0;
100} prng_t;
101
102typedef union
103{
104    uint8_t  b[16];
105    uint32_t w[4];
106#ifdef HAVE_GCC_VECTOR_EXTENSIONS
107    uint8x16 vb;
108    uint32x4 vw;
109#endif
110} prng_rand_128_data_t;
111
112/*****************************************************************************/
113
114static force_inline uint32_t
115smallprng_rand_r (smallprng_t *x)
116{
117    uint32_t e = x->a - ((x->b << 27) + (x->b >> (32 - 27)));
118    x->a = x->b ^ ((x->c << 17) ^ (x->c >> (32 - 17)));
119    x->b = x->c + x->d;
120    x->c = x->d + e;
121    x->d = e + x->a;
122    return x->d;
123}
124
125/* Generate 4 bytes (32-bits) of random data */
126static force_inline uint32_t
127prng_rand_r (prng_t *x)
128{
129    return smallprng_rand_r (&x->p0);
130}
131
132/* Generate 16 bytes (128-bits) of random data */
133static force_inline void
134prng_rand_128_r (prng_t *x, prng_rand_128_data_t *data)
135{
136#ifdef HAVE_GCC_VECTOR_EXTENSIONS
137    uint32x4 e = x->a - ((x->b << 27) + (x->b >> (32 - 27)));
138    x->a = x->b ^ ((x->c << 17) ^ (x->c >> (32 - 17)));
139    x->b = x->c + x->d;
140    x->c = x->d + e;
141    x->d = e + x->a;
142    data->vw = x->d;
143#else
144    data->w[0] = smallprng_rand_r (&x->p1);
145    data->w[1] = smallprng_rand_r (&x->p2);
146    data->w[2] = smallprng_rand_r (&x->p3);
147    data->w[3] = smallprng_rand_r (&x->p4);
148#endif
149}
150
151typedef enum
152{
153    RANDMEMSET_MORE_00        = 1, /* ~25% chance for 0x00 bytes */
154    RANDMEMSET_MORE_FF        = 2, /* ~25% chance for 0xFF bytes */
155    RANDMEMSET_MORE_00000000  = 4, /* ~25% chance for 0x00000000 clusters */
156    RANDMEMSET_MORE_FFFFFFFF  = 8, /* ~25% chance for 0xFFFFFFFF clusters */
157    RANDMEMSET_MORE_00_AND_FF = (RANDMEMSET_MORE_00 | RANDMEMSET_MORE_00000000 |
158                                 RANDMEMSET_MORE_FF | RANDMEMSET_MORE_FFFFFFFF)
159} prng_randmemset_flags_t;
160
161/* Set the 32-bit seed for PRNG */
162void prng_srand_r (prng_t *prng, uint32_t seed);
163
164/* Fill memory buffer with random data */
165void prng_randmemset_r (prng_t                  *prng,
166                        void                    *buffer,
167                        size_t                   size,
168                        prng_randmemset_flags_t  flags);
169
170#endif
171