text: // Copyright (c) 2017 The Bitcoin Core developers
  // Copyright (c) 2017-2019 The Raven Core developers
  // Copyright (c) 2020-2021 The redecoin Core developers
  // Distributed under the MIT software license, see the accompanying
  // file COPYING or http://www.opensource.org/licenses/mit-license.php.
  
  // Based on the public domain implementation 'merged' by D. J. Bernstein
  // See https://cr.yp.to/chacha.html.
  
  #include "crypto/common.h"
  #include "crypto/chacha20.h"
  
  #include <string.h>
  
  constexpr static inline uint32_t rotl32(uint32_t v, int c) { return (v << c) | (v >> (32 - c)); }
  
  #define QUARTERROUND(a,b,c,d) \
    a += b; d = rotl32(d ^ a, 16); \
    c += d; b = rotl32(b ^ c, 12); \
    a += b; d = rotl32(d ^ a, 8); \
    c += d; b = rotl32(b ^ c, 7);
  
  static const unsigned char sigma[] = "expand 32-byte k";
  static const unsigned char tau[] = "expand 16-byte k";
  
  void ChaCha20::SetKey(const unsigned char* k, size_t keylen)
  {
      const unsigned char *constants;
  
      input[4] = ReadLE32(k + 0);
      input[5] = ReadLE32(k + 4);
      input[6] = ReadLE32(k + 8);
      input[7] = ReadLE32(k + 12);
      if (keylen == 32) { /* recommended */
          k += 16;
          constants = sigma;
      } else { /* keylen == 16 */
          constants = tau;
      }
      input[8] = ReadLE32(k + 0);
      input[9] = ReadLE32(k + 4);
      input[10] = ReadLE32(k + 8);
      input[11] = ReadLE32(k + 12);
      input[0] = ReadLE32(constants + 0);
      input[1] = ReadLE32(constants + 4);
      input[2] = ReadLE32(constants + 8);
      input[3] = ReadLE32(constants + 12);
      input[12] = 0;
      input[13] = 0;
      input[14] = 0;
      input[15] = 0;
  }
  
  ChaCha20::ChaCha20()
  {
      memset(input, 0, sizeof(input));
  }
  
  ChaCha20::ChaCha20(const unsigned char* k, size_t keylen)
  {
      SetKey(k, keylen);
  }
  
  void ChaCha20::SetIV(uint64_t iv)
  {
      input[14] = iv;
      input[15] = iv >> 32;
  }
  
  void ChaCha20::Seek(uint64_t pos)
  {
      input[12] = pos;
      input[13] = pos >> 32;
  }
  
  void ChaCha20::Output(unsigned char* c, size_t bytes)
  {
      uint32_t x0, x1, x2, x3, x4, x5, x6, x7, x8, x9, x10, x11, x12, x13, x14, x15;
      uint32_t j0, j1, j2, j3, j4, j5, j6, j7, j8, j9, j10, j11, j12, j13, j14, j15;
      unsigned char *ctarget = nullptr;
      unsigned char tmp[64];
      unsigned int i;
  
      if (!bytes) return;
  
      j0 = input[0];
      j1 = input[1];
      j2 = input[2];
      j3 = input[3];
      j4 = input[4];
      j5 = input[5];
      j6 = input[6];
      j7 = input[7];
      j8 = input[8];
      j9 = input[9];
      j10 = input[10];
      j11 = input[11];
      j12 = input[12];
      j13 = input[13];
      j14 = input[14];
      j15 = input[15];
  
      for (;;) {
          if (bytes < 64) {
              ctarget = c;
              c = tmp;
          }
          x0 = j0;
          x1 = j1;
          x2 = j2;
          x3 = j3;
          x4 = j4;
          x5 = j5;
          x6 = j6;
          x7 = j7;
          x8 = j8;
          x9 = j9;
          x10 = j10;
          x11 = j11;
          x12 = j12;
          x13 = j13;
          x14 = j14;
          x15 = j15;
          for (i = 20;i > 0;i -= 2) {
              QUARTERROUND( x0, x4, x8,x12)
              QUARTERROUND( x1, x5, x9,x13)
              QUARTERROUND( x2, x6,x10,x14)
              QUARTERROUND( x3, x7,x11,x15)
              QUARTERROUND( x0, x5,x10,x15)
              QUARTERROUND( x1, x6,x11,x12)
              QUARTERROUND( x2, x7, x8,x13)
              QUARTERROUND( x3, x4, x9,x14)
          }
          x0 += j0;
          x1 += j1;
          x2 += j2;
          x3 += j3;
          x4 += j4;
          x5 += j5;
          x6 += j6;
          x7 += j7;
          x8 += j8;
          x9 += j9;
          x10 += j10;
          x11 += j11;
          x12 += j12;
          x13 += j13;
          x14 += j14;
          x15 += j15;
  
          ++j12;
          if (!j12) ++j13;
  
          WriteLE32(c + 0, x0);
          WriteLE32(c + 4, x1);
          WriteLE32(c + 8, x2);
          WriteLE32(c + 12, x3);
          WriteLE32(c + 16, x4);
          WriteLE32(c + 20, x5);
          WriteLE32(c + 24, x6);
          WriteLE32(c + 28, x7);
          WriteLE32(c + 32, x8);
          WriteLE32(c + 36, x9);
          WriteLE32(c + 40, x10);
          WriteLE32(c + 44, x11);
          WriteLE32(c + 48, x12);
          WriteLE32(c + 52, x13);
          WriteLE32(c + 56, x14);
          WriteLE32(c + 60, x15);
  
          if (bytes <= 64) {
              if (bytes < 64) {
                  for (i = 0;i < bytes;++i) ctarget[i] = c[i];
              }
              input[12] = j12;
              input[13] = j13;
              return;
          }
          bytes -= 64;
          c += 64;
      }
  }
  