text: /*
   * Copyright (c) 2009 Baptiste Coudurier <baptiste.coudurier@gmail.com>
   *
   * 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 "config.h"
  
  #if HAVE_UNISTD_H
  #include <unistd.h>
  #endif
  #if HAVE_IO_H
  #include <io.h>
  #endif
  #if HAVE_CRYPTGENRANDOM
  #include <windows.h>
  #include <wincrypt.h>
  #endif
  #include <fcntl.h>
  #include <math.h>
  #include <time.h>
  #include <string.h>
  #include "avassert.h"
  #include "internal.h"
  #include "intreadwrite.h"
  #include "timer.h"
  #include "random_seed.h"
  #include "sha.h"
  
  #ifndef TEST
  #define TEST 0
  #endif
  
  static int read_random(uint32_t *dst, const char *file)
  {
  #if HAVE_UNISTD_H
      int fd = avpriv_open(file, O_RDONLY);
      int err = -1;
  
      if (fd == -1)
          return -1;
      err = read(fd, dst, sizeof(*dst));
      close(fd);
  
      return err;
  #else
      return -1;
  #endif
  }
  
  static uint32_t get_generic_seed(void)
  {
      uint8_t tmp[120];
      struct AVSHA *sha = (void*)tmp;
      clock_t last_t  = 0;
      static uint64_t i = 0;
      static uint32_t buffer[512] = { 0 };
      unsigned char digest[20];
      uint64_t last_i = i;
  
      av_assert0(sizeof(tmp) >= av_sha_size);
  
      if(TEST){
          memset(buffer, 0, sizeof(buffer));
          last_i = i = 0;
      }else{
  #ifdef AV_READ_TIME
          buffer[13] ^= AV_READ_TIME();
          buffer[41] ^= AV_READ_TIME()>>32;
  #endif
      }
  
      for (;;) {
          clock_t t = clock();
  
          if (last_t == t) {
              buffer[i & 511]++;
          } else {
              buffer[++i & 511] += (t - last_t) % 3294638521U;
              if (last_i && i - last_i > 4 || i - last_i > 64 || TEST && i - last_i > 8)
                  break;
          }
          last_t = t;
      }
  
      if(TEST) {
          buffer[0] = buffer[1] = 0;
      } else {
  #ifdef AV_READ_TIME
          buffer[111] += AV_READ_TIME();
  #endif
      }
  
      av_sha_init(sha, 160);
      av_sha_update(sha, (const uint8_t *)buffer, sizeof(buffer));
      av_sha_final(sha, digest);
      return AV_RB32(digest) + AV_RB32(digest + 16);
  }
  
  uint32_t av_get_random_seed(void)
  {
      uint32_t seed;
  
  #if HAVE_CRYPTGENRANDOM
      HCRYPTPROV provider;
      if (CryptAcquireContext(&provider, NULL, NULL, PROV_RSA_FULL,
                              CRYPT_VERIFYCONTEXT | CRYPT_SILENT)) {
          BOOL ret = CryptGenRandom(provider, sizeof(seed), (PBYTE) &seed);
          CryptReleaseContext(provider, 0);
          if (ret)
              return seed;
      }
  #endif
  
  #if HAVE_ARC4RANDOM
      return arc4random();
  #endif
  
      if (read_random(&seed, "/dev/urandom") == sizeof(seed))
          return seed;
      if (read_random(&seed, "/dev/random")  == sizeof(seed))
          return seed;
      return get_generic_seed();
  }
  