/*
  * Lagged Fibonacci PRNG
  * Copyright (c) 2008 Michael Niedermayer
  *
  * This file is part of FFmpeg.
  *
  * FFmpeg is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
  * License as published by the Free Software Foundation; either
  * version 2.1 of the License, or (at your option) any later version.
  *
  * FFmpeg is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * Lesser General Public License for more details.
  *
  * You should have received a copy of the GNU Lesser General Public
  * License along with FFmpeg; if not, write to the Free Software
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
 #include <inttypes.h>

 #include <limits.h>
 #include <math.h>

 #include "lfg.h"
 #include "md5.h"
 #include "intreadwrite.h"

 #include "attributes.h"

 av_cold void av_lfg_init(AVLFG *c, unsigned int seed)

 {
     uint8_t tmp[16] = { 0 };

     int i;
 

     for (i = 8; i < 64; i += 4) {
         AV_WL32(tmp, seed);
         tmp[4] = i;
         av_md5_sum(tmp, tmp, 16);
         c->state[i    ] = AV_RL32(tmp);
         c->state[i + 1] = AV_RL32(tmp + 4);
         c->state[i + 2] = AV_RL32(tmp + 8);
         c->state[i + 3] = AV_RL32(tmp + 12);

     }

     c->index = 0;

 }
 

 void av_bmg_get(AVLFG *lfg, double out[2])
 {
     double x1, x2, w;
 
     do {

         x1 = 2.0 / UINT_MAX * av_lfg_get(lfg) - 1.0;
         x2 = 2.0 / UINT_MAX * av_lfg_get(lfg) - 1.0;
         w  = x1 * x1 + x2 * x2;

     } while (w >= 1.0);
 
     w = sqrt((-2.0 * log(w)) / w);
     out[0] = x1 * w;
     out[1] = x2 * w;
 }
 

 #ifdef TEST
 #include "log.h"

 #include "timer.h"

 
 int main(void)
 {

     int x = 0;

     int i, j;
     AVLFG state;
 
     av_lfg_init(&state, 0xdeadbeef);
     for (j = 0; j < 10000; j++) {
         START_TIMER
         for (i = 0; i < 624; i++) {

             //av_log(NULL, AV_LOG_ERROR, "%X\n", av_lfg_get(&state));
             x += av_lfg_get(&state);

         }

         STOP_TIMER("624 calls of av_lfg_get");

     }
     av_log(NULL, AV_LOG_ERROR, "final value:%X\n", x);

 
     /* BMG usage example */
     {
         double mean   = 1000;
         double stddev = 53;
 
         av_lfg_init(&state, 42);
 
         for (i = 0; i < 1000; i += 2) {
             double bmg_out[2];
             av_bmg_get(&state, bmg_out);
             av_log(NULL, AV_LOG_INFO,
                    "%f\n%f\n",
                    bmg_out[0] * stddev + mean,
                    bmg_out[1] * stddev + mean);
         }
     }
 

     return 0;
 }
 #endif