github.com/shopperooofficial/ethereum-protocol@v1.9.7/crypto/secp256k1/libsecp256k1/src/testrand_impl.h (about)

     1  /**********************************************************************
     2   * Copyright (c) 2013-2015 Pieter Wuille                              *
     3   * Distributed under the MIT software license, see the accompanying   *
     4   * file COPYING or http://www.opensource.org/licenses/mit-license.php.*
     5   **********************************************************************/
     6  
     7  #ifndef _SECP256K1_TESTRAND_IMPL_H_
     8  #define _SECP256K1_TESTRAND_IMPL_H_
     9  
    10  #include <stdint.h>
    11  #include <string.h>
    12  
    13  #include "testrand.h"
    14  #include "hash.h"
    15  
    16  static secp256k1_rfc6979_hmac_sha256_t secp256k1_test_rng;
    17  static uint32_t secp256k1_test_rng_precomputed[8];
    18  static int secp256k1_test_rng_precomputed_used = 8;
    19  static uint64_t secp256k1_test_rng_integer;
    20  static int secp256k1_test_rng_integer_bits_left = 0;
    21  
    22  SECP256K1_INLINE static void secp256k1_rand_seed(const unsigned char *seed16) {
    23      secp256k1_rfc6979_hmac_sha256_initialize(&secp256k1_test_rng, seed16, 16);
    24  }
    25  
    26  SECP256K1_INLINE static uint32_t secp256k1_rand32(void) {
    27      if (secp256k1_test_rng_precomputed_used == 8) {
    28          secp256k1_rfc6979_hmac_sha256_generate(&secp256k1_test_rng, (unsigned char*)(&secp256k1_test_rng_precomputed[0]), sizeof(secp256k1_test_rng_precomputed));
    29          secp256k1_test_rng_precomputed_used = 0;
    30      }
    31      return secp256k1_test_rng_precomputed[secp256k1_test_rng_precomputed_used++];
    32  }
    33  
    34  static uint32_t secp256k1_rand_bits(int bits) {
    35      uint32_t ret;
    36      if (secp256k1_test_rng_integer_bits_left < bits) {
    37          secp256k1_test_rng_integer |= (((uint64_t)secp256k1_rand32()) << secp256k1_test_rng_integer_bits_left);
    38          secp256k1_test_rng_integer_bits_left += 32;
    39      }
    40      ret = secp256k1_test_rng_integer;
    41      secp256k1_test_rng_integer >>= bits;
    42      secp256k1_test_rng_integer_bits_left -= bits;
    43      ret &= ((~((uint32_t)0)) >> (32 - bits));
    44      return ret;
    45  }
    46  
    47  static uint32_t secp256k1_rand_int(uint32_t range) {
    48      /* We want a uniform integer between 0 and range-1, inclusive.
    49       * B is the smallest number such that range <= 2**B.
    50       * two mechanisms implemented here:
    51       * - generate B bits numbers until one below range is found, and return it
    52       * - find the largest multiple M of range that is <= 2**(B+A), generate B+A
    53       *   bits numbers until one below M is found, and return it modulo range
    54       * The second mechanism consumes A more bits of entropy in every iteration,
    55       * but may need fewer iterations due to M being closer to 2**(B+A) then
    56       * range is to 2**B. The array below (indexed by B) contains a 0 when the
    57       * first mechanism is to be used, and the number A otherwise.
    58       */
    59      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};
    60      uint32_t trange, mult;
    61      int bits = 0;
    62      if (range <= 1) {
    63          return 0;
    64      }
    65      trange = range - 1;
    66      while (trange > 0) {
    67          trange >>= 1;
    68          bits++;
    69      }
    70      if (addbits[bits]) {
    71          bits = bits + addbits[bits];
    72          mult = ((~((uint32_t)0)) >> (32 - bits)) / range;
    73          trange = range * mult;
    74      } else {
    75          trange = range;
    76          mult = 1;
    77      }
    78      while(1) {
    79          uint32_t x = secp256k1_rand_bits(bits);
    80          if (x < trange) {
    81              return (mult == 1) ? x : (x % range);
    82          }
    83      }
    84  }
    85  
    86  static void secp256k1_rand256(unsigned char *b32) {
    87      secp256k1_rfc6979_hmac_sha256_generate(&secp256k1_test_rng, b32, 32);
    88  }
    89  
    90  static void secp256k1_rand_bytes_test(unsigned char *bytes, size_t len) {
    91      size_t bits = 0;
    92      memset(bytes, 0, len);
    93      while (bits < len * 8) {
    94          int now;
    95          uint32_t val;
    96          now = 1 + (secp256k1_rand_bits(6) * secp256k1_rand_bits(5) + 16) / 31;
    97          val = secp256k1_rand_bits(1);
    98          while (now > 0 && bits < len * 8) {
    99              bytes[bits / 8] |= val << (bits % 8);
   100              now--;
   101              bits++;
   102          }
   103      }
   104  }
   105  
   106  static void secp256k1_rand256_test(unsigned char *b32) {
   107      secp256k1_rand_bytes_test(b32, 32);
   108  }
   109  
   110  #endif