171 lines
5.9 KiB
C
171 lines
5.9 KiB
C
/*
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* Copyright © 2012 Siarhei Siamashka <siarhei.siamashka@gmail.com>
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*
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* Based on the public domain implementation of small noncryptographic PRNG
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* authored by Bob Jenkins: http://burtleburtle.net/bob/rand/smallprng.html
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*
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* Permission is hereby granted, free of charge, to any person obtaining a
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* copy of this software and associated documentation files (the "Software"),
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* to deal in the Software without restriction, including without limitation
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* the rights to use, copy, modify, merge, publish, distribute, sublicense,
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* and/or sell copies of the Software, and to permit persons to whom the
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* Software is furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice (including the next
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* paragraph) shall be included in all copies or substantial portions of the
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* Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
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* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
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* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
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* DEALINGS IN THE SOFTWARE.
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*/
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#ifndef __UTILS_PRNG_H__
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#define __UTILS_PRNG_H__
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/*
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* This file provides a fast SIMD-optimized noncryptographic PRNG (pseudorandom
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* number generator), with the output good enough to pass "Big Crush" tests
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* from TestU01 (http://en.wikipedia.org/wiki/TestU01).
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*
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* SIMD code uses http://gcc.gnu.org/onlinedocs/gcc/Vector-Extensions.html
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* which is a GCC specific extension. There is also a slower alternative
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* code path, which should work with any C compiler.
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*
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* The "prng_t" structure keeps the internal state of the random number
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* generator. It is possible to have multiple instances of the random number
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* generator active at the same time, in this case each of them needs to have
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* its own "prng_t". All the functions take a pointer to "prng_t"
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* as the first argument.
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*
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* Functions:
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*
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* ----------------------------------------------------------------------------
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* void prng_srand_r (prng_t *prng, uint32_t seed);
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*
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* Initialize the pseudorandom number generator. The sequence of preudorandom
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* numbers is deterministic and only depends on "seed". Any two generators
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* initialized with the same seed will produce exactly the same sequence.
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*
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* ----------------------------------------------------------------------------
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* uint32_t prng_rand_r (prng_t *prng);
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*
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* Generate a single uniformly distributed 32-bit pseudorandom value.
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*
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* ----------------------------------------------------------------------------
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* void prng_randmemset_r (prng_t *prng,
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* void *buffer,
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* size_t size,
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* prng_randmemset_flags_t flags);
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*
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* Fills the memory buffer "buffer" with "size" bytes of pseudorandom data.
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* The "flags" argument may be used to tweak some statistics properties:
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* RANDMEMSET_MORE_00 - set ~25% of bytes to 0x00
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* RANDMEMSET_MORE_FF - set ~25% of bytes to 0xFF
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* The flags can be combined. This allows a bit better simulation of typical
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* pixel data, which normally contains a lot of fully transparent or fully
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* opaque pixels.
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*/
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#ifdef HAVE_CONFIG_H
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#include <config.h>
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#endif
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#include "pixman-private.h"
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/*****************************************************************************/
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#ifdef HAVE_GCC_VECTOR_EXTENSIONS
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typedef uint32_t uint32x4 __attribute__ ((vector_size(16)));
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typedef uint8_t uint8x16 __attribute__ ((vector_size(16)));
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#endif
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typedef struct
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{
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uint32_t a, b, c, d;
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} smallprng_t;
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typedef struct
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{
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#ifdef HAVE_GCC_VECTOR_EXTENSIONS
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uint32x4 a, b, c, d;
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#else
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smallprng_t p1, p2, p3, p4;
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#endif
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smallprng_t p0;
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} prng_t;
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typedef union
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{
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uint8_t b[16];
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uint32_t w[4];
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#ifdef HAVE_GCC_VECTOR_EXTENSIONS
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uint8x16 vb;
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uint32x4 vw;
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#endif
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} prng_rand_128_data_t;
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/*****************************************************************************/
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static force_inline uint32_t
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smallprng_rand_r (smallprng_t *x)
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{
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uint32_t e = x->a - ((x->b << 27) + (x->b >> (32 - 27)));
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x->a = x->b ^ ((x->c << 17) ^ (x->c >> (32 - 17)));
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x->b = x->c + x->d;
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x->c = x->d + e;
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x->d = e + x->a;
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return x->d;
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}
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/* Generate 4 bytes (32-bits) of random data */
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static force_inline uint32_t
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prng_rand_r (prng_t *x)
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{
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return smallprng_rand_r (&x->p0);
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}
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/* Generate 16 bytes (128-bits) of random data */
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static force_inline void
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prng_rand_128_r (prng_t *x, prng_rand_128_data_t *data)
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{
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#ifdef HAVE_GCC_VECTOR_EXTENSIONS
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uint32x4 e = x->a - ((x->b << 27) + (x->b >> (32 - 27)));
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x->a = x->b ^ ((x->c << 17) ^ (x->c >> (32 - 17)));
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x->b = x->c + x->d;
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x->c = x->d + e;
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x->d = e + x->a;
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data->vw = x->d;
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#else
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data->w[0] = smallprng_rand_r (&x->p1);
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data->w[1] = smallprng_rand_r (&x->p2);
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data->w[2] = smallprng_rand_r (&x->p3);
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data->w[3] = smallprng_rand_r (&x->p4);
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#endif
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}
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typedef enum
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{
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RANDMEMSET_MORE_00 = 1, /* ~25% chance for 0x00 bytes */
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RANDMEMSET_MORE_FF = 2, /* ~25% chance for 0xFF bytes */
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RANDMEMSET_MORE_00000000 = 4, /* ~25% chance for 0x00000000 clusters */
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RANDMEMSET_MORE_FFFFFFFF = 8, /* ~25% chance for 0xFFFFFFFF clusters */
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RANDMEMSET_MORE_00_AND_FF = (RANDMEMSET_MORE_00 | RANDMEMSET_MORE_00000000 |
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RANDMEMSET_MORE_FF | RANDMEMSET_MORE_FFFFFFFF)
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} prng_randmemset_flags_t;
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/* Set the 32-bit seed for PRNG */
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void prng_srand_r (prng_t *prng, uint32_t seed);
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/* Fill memory buffer with random data */
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void prng_randmemset_r (prng_t *prng,
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void *buffer,
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size_t size,
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prng_randmemset_flags_t flags);
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#endif
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