text: /*
   * Copyright (c) 2014-2015 ARM Limited. All rights reserved.
   * SPDX-License-Identifier: Apache-2.0
   * Licensed under the Apache License, Version 2.0 (the License); you may
   * not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   * http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an AS IS BASIS, WITHOUT
   * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  #include <stdint.h>
  #include <limits.h>
  #include "randLIB.h"
  #include "platform/arm_hal_random.h"
  
  /**
   * This library is made for getting random numbers for timing needs in
   * protocols, plus to generate dynamic ports, random IDs etc.
   *
   * **not safe to use for security or cryptographic operations.**
   *
   * Base implementation is a pseudo-RNG, but may also use a system RNG.
   * Replay of sequence by reseeding is not possible.
   *
   * Base pseudo-RNG is the xoroshiro128+ generator by Marsaglia, Blackman and
   * Vigna:
   *
   * http://xoroshiro.di.unimi.it/
   *
   * Certainly not the fastest for 32-bit or smaller platforms, but speed
   * is not critical. None of the long operations in the core are actually hard,
   * unlike the divisions and multiplies in the utility functions below, where we
   * do try to keep the operations narrow.
   */
  
  /* On some platforms, read from a system RNG, rather than use our own */
  /* RANDLIB_PRNG disables this and forces use of the PRNG (useful for test only?) */
  #ifndef RANDLIB_PRNG
  #ifdef __linux
  #define RANDOM_DEVICE "/dev/urandom"
  #endif
  #endif // RANDLIB_PRNG
  
  /* RAM usage - 16 bytes of state (or a FILE * pointer and underlying FILE, which
   * will include a buffer) */
  #ifdef RANDOM_DEVICE
  #include <stdio.h>
  static FILE *random_file;
  #else
  static uint64_t state[2];
  #endif
  
  #ifdef RANDLIB_PRNG
  void randLIB_reset(void)
  {
      state[0] = 0;
      state[1] = 0;
  }
  #endif
  
  #ifndef RANDOM_DEVICE
  static inline uint64_t rol(uint64_t n, int bits)
  {
      return (n << bits) | (n >> (64 - bits));
  }
  
  /* Lower-quality generator used only for initial seeding, if platform
   * isn't returning multiple seeds itself. Multiplies are rather heavy
   * for lower-end platforms, but this is initialisation only.
   */
  static uint64_t splitmix64(uint64_t *seed)
  {
      uint64_t z = (*seed += UINT64_C(0x9E3779B97F4A7C15));
      z = (z ^ (z >> 30)) * UINT64_C(0xBF58476D1CE4E5B9);
      z = (z ^ (z >> 27)) * UINT64_C(0x94D049BB133111EB);
      return z ^ (z >> 31);
  }
  #endif // RANDOM_DEVICE
  
  void randLIB_seed_random(void)
  {
  #ifdef RANDOM_DEVICE
      if (!random_file) {
          random_file = fopen(RANDOM_DEVICE, "rb");
      }
  #else
      arm_random_module_init();
  
      /* We exclusive-OR with the current state, in case they make this call
       * multiple times,or in case someone has called randLIB_add_seed before
       * this. We don't want to potentially lose entropy.
       */
  
      /* Spell out expressions so we get known ordering of 4 seed calls */
      uint64_t s = (uint64_t) arm_random_seed_get() << 32;
      state[0] ^= ( s | arm_random_seed_get());
  
      s = (uint64_t) arm_random_seed_get() << 32;
      state[1] ^= s | arm_random_seed_get();
  
      /* This check serves to both to stir the state if the platform is returning
       * constant seeding values, and to avoid the illegal all-zero state.
       */
      if (state[0] == state[1]) {
          randLIB_add_seed(state[0]);
      }
  #endif // RANDOM_DEVICE
  }
  
  void randLIB_add_seed(uint64_t seed)
  {
  #ifndef RANDOM_DEVICE
      state[0] ^= splitmix64(&seed);
      state[1] ^= splitmix64(&seed);
      /* This is absolutely necessary, but I challenge you to add it to line coverage */
      if (state[1] == 0 && state[0] == 0) {
          state[0] = 1;
      }
  #else
      (void)seed;
  #endif
  }
  
  uint8_t randLIB_get_8bit(void)
  {
      uint64_t r = randLIB_get_64bit();
      return (uint8_t) (r >> 56);
  }
  
  uint16_t randLIB_get_16bit(void)
  {
      uint64_t r = randLIB_get_64bit();
      return (uint16_t) (r >> 48);
  }
  
  uint32_t randLIB_get_32bit(void)
  {
      uint64_t r = randLIB_get_64bit();
      return (uint32_t) (r >> 32);
  }
  
  
  uint64_t randLIB_get_64bit(void)
  {
  #ifdef RANDOM_DEVICE
      if (!random_file) {
          return 0;
      }
      uint64_t result;
      if (fread(&result, sizeof result, 1, random_file) != 1) {
          result = 0;
      }
      return result;
  #else
      const uint64_t s0 = state[0];
      uint64_t s1 = state[1];
      const uint64_t result = s0 + s1;
  
      s1 ^= s0;
      state[0] = rol(s0, 55) ^ s1 ^ (s1 << 14);
      state[1] = rol(s1, 36);
  
      return result;
  #endif
  }
  
  void *randLIB_get_n_bytes_random(void *ptr, uint8_t count)
  {
      uint8_t *data_ptr = ptr;
      uint64_t r = 0;
      for (uint_fast8_t i = 0; i < count; i++) {
          /* Take 8 bytes at a time */
          if (i % 8 == 0) {
              r = randLIB_get_64bit();
          } else {
              r >>= 8;
          }
          data_ptr[i] = (uint8_t) r;
      }
      return data_ptr;
  }
  
  uint16_t randLIB_get_random_in_range(uint16_t min, uint16_t max)
  {
      /* This special case is potentially common, particularly in this routine's
       * first user (Trickle), so worth catching immediately */
      if (min == max) {
          return min;
      }
  
  #if UINT_MAX >= 0xFFFFFFFF
      const unsigned int rand_max = 0xFFFFFFFFu; // will use rand32
  #else
      const unsigned int rand_max = 0xFFFFu; // will use rand16
  
      /* 16-bit arithmetic below fails in this extreme case; we can optimise it */
      if (max - min == 0xFFFF) {
          return randLIB_get_16bit();
      }
  #endif
  
      /* We get rand_max values from rand16 or 32() in the range [0..rand_max-1], and
       * need to divvy them up into the number of values we need. And reroll any
       * odd values off the end as we insist every value having equal chance.
       *
       * Using the range [0..rand_max-1] saves long division on the band
       * calculation - it means rand_max ends up always being rerolled.
       *
       * Eg, range(1,2), rand_max = 0xFFFF:
       * We have 2 bands of size 0x7FFF (0xFFFF/2).
       *
       * We roll: 0x0000..0x7FFE -> 1
       *          0x7FFF..0xFFFD -> 2
       *          0xFFFE..0xFFFF -> reroll
       * (calculating band size as 0x10000/2 would have avoided the reroll cases)
       *
       * Eg, range(1,3), rand_max = 0xFFFFFFFF:
       * We have 3 bands of size 0x55555555 (0xFFFFFFFF/3).
       *
       * We roll: 0x00000000..0x555555554 -> 1
       *          0x55555555..0xAAAAAAAA9 -> 2
       *          0xAAAAAAAA..0xFFFFFFFFE -> 3
       *          0xFFFFFFFF              -> reroll
       *
       * (Bias problem clearly pretty insignificant there, but gets worse as
       * range increases).
       */
      const unsigned int values_needed = max + 1 - min;
      /* Avoid the need for long division, at the expense of fractionally
       * increasing reroll chance. */
      const unsigned int band_size = rand_max / values_needed;
      const unsigned int top_of_bands = band_size * values_needed;
      unsigned int result;
      do {
  #if UINT_MAX > 0xFFFF
          result = randLIB_get_32bit();
  #else
          result = randLIB_get_16bit();
  #endif
      } while (result >= top_of_bands);
  
      return min + (uint16_t)(result / band_size);
  }
  
  uint32_t randLIB_randomise_base(uint32_t base, uint16_t min_factor, uint16_t max_factor)
  {
      uint16_t random_factor = randLIB_get_random_in_range(min_factor, max_factor);
  
      /* 32x16-bit long multiplication, to get 48-bit result */
      uint32_t hi = (base >> 16) * random_factor;
      uint32_t lo = (base & 0xFFFF) * random_factor;
      /* Add halves, and take top 32 bits of 48-bit result */
      uint32_t res = hi + (lo >> 16);
  
      /* Randomisation factor is *2^15, so need to shift up 1 more bit, avoiding overflow */
      if (res & 0x80000000) {
          res = 0xFFFFFFFF;
      } else {
          res = (res << 1) | ((lo >> 15) & 1);
      }
  
      return res;
  }
  