1 /*

     2  * Lagged Fibonacci PRNG

     3  * Copyright (c) 2008 Michael Niedermayer

     4  *

     5  * This file is part of Libav.

     6  *

     7  * Libav is free software; you can redistribute it and/or

     8  * modify it under the terms of the GNU Lesser General Public

     9  * License as published by the Free Software Foundation; either

    10  * version 2.1 of the License, or (at your option) any later version.

    11  *

    12  * Libav is distributed in the hope that it will be useful,

    13  * but WITHOUT ANY WARRANTY; without even the implied warranty of

    14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

    15  * Lesser General Public License for more details.

    16  *

    17  * You should have received a copy of the GNU Lesser General Public

    18  * License along with Libav; if not, write to the Free Software

    19  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA

    20  */

    21 

    22 #ifndef AVUTIL_LFG_H

    23 #define AVUTIL_LFG_H

    24 

    25 typedef struct AVLFG {

    26     unsigned int state[64];

    27     int index;

    28 } AVLFG;

    29 

    30 void av_lfg_init(AVLFG *c, unsigned int seed);

    31 

    32 /**

    33  * Get the next random unsigned 32-bit number using an ALFG.

    34  *

    35  * Please also consider a simple LCG like state= state*1664525+1013904223,

    36  * it may be good enough and faster for your specific use case.

    37  */

    38 static inline unsigned int av_lfg_get(AVLFG *c){

    39     c->state[c->index & 63] = c->state[(c->index-24) & 63] + c->state[(c->index-55) & 63];

    40     return c->state[c->index++ & 63];

    41 }

    42 

    43 /**

    44  * Get the next random unsigned 32-bit number using a MLFG.

    45  *

    46  * Please also consider av_lfg_get() above, it is faster.

    47  */

    48 static inline unsigned int av_mlfg_get(AVLFG *c){

    49     unsigned int a= c->state[(c->index-55) & 63];

    50     unsigned int b= c->state[(c->index-24) & 63];

    51     return c->state[c->index++ & 63] = 2*a*b+a+b;

    52 }

    53 

    54 /**

    55  * Get the next two numbers generated by a Box-Muller Gaussian

    56  * generator using the random numbers issued by lfg.

    57  *

    58  * @param out array where the two generated numbers are placed

    59  */

    60 void av_bmg_get(AVLFG *lfg, double out[2]);

    61 

    62 #endif /* AVUTIL_LFG_H */