//

// Random number function for CUPS.

//

// Copyright © 2019-2022 by Michael R Sweet.

//

// Licensed under Apache License v2.0.  See the file "LICENSE" for more

// information.

//

#include "cups.h"

#if !defined(_WIN32) && !defined(__APPLE__)

#  include <unistd.h>

#  include <fcntl.h>

#  include <pthread.h>

#endif // !_WIN32 && !__APPLE__

//

// 'cupsGetRand()' - Return a 32-bit pseudo-random number.

//

// This function returns a 32-bit pseudo-random number suitable for use as

// one-time identifiers or nonces.  The random numbers are generated/seeded

// using system entropy.

//

unsigned        // O - Random number

cupsGetRand(void)

{

#if _WIN32

  // rand_s uses real entropy...

  unsigned v;       // Random number

  rand_s(&v);

  return (v);

#elif defined(__APPLE__)

  // macOS/iOS arc4random() uses real entropy automatically...

  return (arc4random());

#else

  // Use a Mersenne twister random number generator seeded from /dev/urandom...

  unsigned  i,      // Looping var

    temp;     // Temporary value

  static bool first_time = true;  // First time we ran?

  static unsigned mt_state[624],  // Mersenne twister state

    mt_index;   // Mersenne twister index

  static pthread_mutex_t mt_mutex = PTHREAD_MUTEX_INITIALIZER;

          // Mutex to control access to state

  pthread_mutex_lock(&mt_mutex);

  if (first_time)

  {

    int   fd;     // "/dev/urandom" file

    struct timeval curtime;   // Current time

    // Seed the random number state...

    if ((fd = open("/dev/urandom", O_RDONLY)) >= 0)

    {

      // Read random entropy from the system...

      if (read(fd, mt_state, sizeof(mt_state[0])) < sizeof(mt_state[0]))

        mt_state[0] = 0;   // Force fallback...

      close(fd);

    }

    else

      mt_state[0] = 0;

    if (!mt_state[0])

    {

      // Fallback to using the current time in microseconds...

      gettimeofday(&curtime, NULL);

      mt_state[0] = (unsigned)(curtime.tv_sec + curtime.tv_usec);

    }

    mt_index = 0;

    for (i = 1; i < 624; i ++)

      mt_state[i] = (unsigned)((1812433253 * (mt_state[i - 1] ^ (mt_state[i - 1] >> 30))) + i);

    first_time = false;

  }

  if (mt_index == 0)

  {

    // Generate a sequence of random numbers...

    unsigned i1 = 1, i397 = 397;  // Looping vars

    for (i = 0; i < 624; i ++)

    {

      temp        = (mt_state[i] & 0x80000000) + (mt_state[i1] & 0x7fffffff);

      mt_state[i] = mt_state[i397] ^ (temp >> 1);

      if (temp & 1)

  mt_state[i] ^= 2567483615u;

      i1 ++;

      i397 ++;

      if (i1 == 624)

  i1 = 0;

      if (i397 == 624)

  i397 = 0;

    }

  }

  // Pull 32-bits of random data...

  temp = mt_state[mt_index ++];

  temp ^= temp >> 11;

  temp ^= (temp << 7) & 2636928640u;

  temp ^= (temp << 15) & 4022730752u;

  temp ^= temp >> 18;

  if (mt_index == 624)

    mt_index = 0;

  pthread_mutex_unlock(&mt_mutex);

  return (temp);

#endif // _WIN32

}