text: /**********************************************************************
   * Copyright (c) 2013-2015 Pieter Wuille                              *
   * Distributed under the MIT software license, see the accompanying   *
   * file COPYING or http://www.opensource.org/licenses/mit-license.php.*
   **********************************************************************/
  
  #ifndef SECP256K1_TESTRAND_IMPL_H
  #define SECP256K1_TESTRAND_IMPL_H
  
  #include <stdint.h>
  #include <string.h>
  
  #include "testrand.h"
  #include "hash.h"
  
  static rustsecp256k1_v0_2_0_rfc6979_hmac_sha256 rustsecp256k1_v0_2_0_test_rng;
  static uint32_t rustsecp256k1_v0_2_0_test_rng_precomputed[8];
  static int rustsecp256k1_v0_2_0_test_rng_precomputed_used = 8;
  static uint64_t rustsecp256k1_v0_2_0_test_rng_integer;
  static int rustsecp256k1_v0_2_0_test_rng_integer_bits_left = 0;
  
  SECP256K1_INLINE static void rustsecp256k1_v0_2_0_rand_seed(const unsigned char *seed16) {
      rustsecp256k1_v0_2_0_rfc6979_hmac_sha256_initialize(&rustsecp256k1_v0_2_0_test_rng, seed16, 16);
  }
  
  SECP256K1_INLINE static uint32_t rustsecp256k1_v0_2_0_rand32(void) {
      if (rustsecp256k1_v0_2_0_test_rng_precomputed_used == 8) {
          rustsecp256k1_v0_2_0_rfc6979_hmac_sha256_generate(&rustsecp256k1_v0_2_0_test_rng, (unsigned char*)(&rustsecp256k1_v0_2_0_test_rng_precomputed[0]), sizeof(rustsecp256k1_v0_2_0_test_rng_precomputed));
          rustsecp256k1_v0_2_0_test_rng_precomputed_used = 0;
      }
      return rustsecp256k1_v0_2_0_test_rng_precomputed[rustsecp256k1_v0_2_0_test_rng_precomputed_used++];
  }
  
  static uint32_t rustsecp256k1_v0_2_0_rand_bits(int bits) {
      uint32_t ret;
      if (rustsecp256k1_v0_2_0_test_rng_integer_bits_left < bits) {
          rustsecp256k1_v0_2_0_test_rng_integer |= (((uint64_t)rustsecp256k1_v0_2_0_rand32()) << rustsecp256k1_v0_2_0_test_rng_integer_bits_left);
          rustsecp256k1_v0_2_0_test_rng_integer_bits_left += 32;
      }
      ret = rustsecp256k1_v0_2_0_test_rng_integer;
      rustsecp256k1_v0_2_0_test_rng_integer >>= bits;
      rustsecp256k1_v0_2_0_test_rng_integer_bits_left -= bits;
      ret &= ((~((uint32_t)0)) >> (32 - bits));
      return ret;
  }
  
  static uint32_t rustsecp256k1_v0_2_0_rand_int(uint32_t range) {
      /* We want a uniform integer between 0 and range-1, inclusive.
       * B is the smallest number such that range <= 2**B.
       * two mechanisms implemented here:
       * - generate B bits numbers until one below range is found, and return it
       * - find the largest multiple M of range that is <= 2**(B+A), generate B+A
       *   bits numbers until one below M is found, and return it modulo range
       * The second mechanism consumes A more bits of entropy in every iteration,
       * but may need fewer iterations due to M being closer to 2**(B+A) then
       * range is to 2**B. The array below (indexed by B) contains a 0 when the
       * first mechanism is to be used, and the number A otherwise.
       */
      static const int addbits[] = {0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 2, 2, 2, 2, 2, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 2, 1, 0};
      uint32_t trange, mult;
      int bits = 0;
      if (range <= 1) {
          return 0;
      }
      trange = range - 1;
      while (trange > 0) {
          trange >>= 1;
          bits++;
      }
      if (addbits[bits]) {
          bits = bits + addbits[bits];
          mult = ((~((uint32_t)0)) >> (32 - bits)) / range;
          trange = range * mult;
      } else {
          trange = range;
          mult = 1;
      }
      while(1) {
          uint32_t x = rustsecp256k1_v0_2_0_rand_bits(bits);
          if (x < trange) {
              return (mult == 1) ? x : (x % range);
          }
      }
  }
  
  static void rustsecp256k1_v0_2_0_rand256(unsigned char *b32) {
      rustsecp256k1_v0_2_0_rfc6979_hmac_sha256_generate(&rustsecp256k1_v0_2_0_test_rng, b32, 32);
  }
  
  static void rustsecp256k1_v0_2_0_rand_bytes_test(unsigned char *bytes, size_t len) {
      size_t bits = 0;
      memset(bytes, 0, len);
      while (bits < len * 8) {
          int now;
          uint32_t val;
          now = 1 + (rustsecp256k1_v0_2_0_rand_bits(6) * rustsecp256k1_v0_2_0_rand_bits(5) + 16) / 31;
          val = rustsecp256k1_v0_2_0_rand_bits(1);
          while (now > 0 && bits < len * 8) {
              bytes[bits / 8] |= val << (bits % 8);
              now--;
              bits++;
          }
      }
  }
  
  static void rustsecp256k1_v0_2_0_rand256_test(unsigned char *b32) {
      rustsecp256k1_v0_2_0_rand_bytes_test(b32, 32);
  }
  
  #endif /* SECP256K1_TESTRAND_IMPL_H */
  