text: // Copyrights(c) 2017-2018, The Electroneum Project
  // Copyrights(c) 2014-2017, The Monero Project
  // 
  // All rights reserved.
  // 
  // Redistribution and use in source and binary forms, with or without modification, are
  // permitted provided that the following conditions are met:
  // 
  // 1. Redistributions of source code must retain the above copyright notice, this list of
  //    conditions and the following disclaimer.
  // 
  // 2. Redistributions in binary form must reproduce the above copyright notice, this list
  //    of conditions and the following disclaimer in the documentation and/or other
  //    materials provided with the distribution.
  // 
  // 3. Neither the name of the copyright holder nor the names of its contributors may be
  //    used to endorse or promote products derived from this software without specific
  //    prior written permission.
  // 
  // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY
  // EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
  // MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
  // THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
  // PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
  // INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
  // STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
  // THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  // 
  // Parts of this file are originally copyright (c) 2012-2013 The Cryptonote developers
  
  #include <assert.h>
  #include <stddef.h>
  #include <string.h>
  
  #include "hash-ops.h"
  #include "initializer.h"
  #include "random.h"
  
  static void generate_system_random_bytes(size_t n, void *result);
  
  #if defined(_WIN32)
  
  #include <windows.h>
  #include <wincrypt.h>
  
  static void generate_system_random_bytes(size_t n, void *result) {
    HCRYPTPROV prov;
  #define must_succeed(x) do if (!(x)) abort(); while (0)
    must_succeed(CryptAcquireContext(&prov, NULL, NULL, PROV_RSA_FULL, CRYPT_VERIFYCONTEXT | CRYPT_SILENT));
    must_succeed(CryptGenRandom(prov, (DWORD)n, result));
    must_succeed(CryptReleaseContext(prov, 0));
  #undef must_succeed
  }
  
  #else
  
  #include <err.h>
  #include <errno.h>
  #include <fcntl.h>
  #include <stdlib.h>
  #include <sys/stat.h>
  #include <sys/types.h>
  #include <unistd.h>
  
  static void generate_system_random_bytes(size_t n, void *result) {
    int fd;
    if ((fd = open("/dev/urandom", O_RDONLY | O_NOCTTY | O_CLOEXEC)) < 0) {
      err(EXIT_FAILURE, "open /dev/urandom");
    }
    for (;;) {
      ssize_t res = read(fd, result, n);
      if ((size_t) res == n) {
        break;
      }
      if (res < 0) {
        if (errno != EINTR) {
          err(EXIT_FAILURE, "read /dev/urandom");
        }
      } else if (res == 0) {
        errx(EXIT_FAILURE, "read /dev/urandom: end of file");
      } else {
        result = padd(result, (size_t) res);
        n -= (size_t) res;
      }
    }
    if (close(fd) < 0) {
      err(EXIT_FAILURE, "close /dev/urandom");
    }
  }
  
  #endif
  
  static union hash_state state;
  
  #if !defined(NDEBUG)
  static volatile int curstate; /* To catch thread safety problems. */
  #endif
  
  FINALIZER(deinit_random) {
  #if !defined(NDEBUG)
    assert(curstate == 1);
    curstate = 0;
  #endif
    memset(&state, 0, sizeof(union hash_state));
  }
  
  INITIALIZER(init_random) {
    generate_system_random_bytes(32, &state);
    REGISTER_FINALIZER(deinit_random);
  #if !defined(NDEBUG)
    assert(curstate == 0);
    curstate = 1;
  #endif
  }
  
  void generate_random_bytes_not_thread_safe(size_t n, void *result) {
  #if !defined(NDEBUG)
    assert(curstate == 1);
    curstate = 2;
  #endif
    if (n == 0) {
  #if !defined(NDEBUG)
      assert(curstate == 2);
      curstate = 1;
  #endif
      return;
    }
    for (;;) {
      hash_permutation(&state);
      if (n <= HASH_DATA_AREA) {
        memcpy(result, &state, n);
  #if !defined(NDEBUG)
        assert(curstate == 2);
        curstate = 1;
  #endif
        return;
      } else {
        memcpy(result, &state, HASH_DATA_AREA);
        result = padd(result, HASH_DATA_AREA);
        n -= HASH_DATA_AREA;
      }
    }
  }
  