text: // Copyright (c) 2020 The Widecoin Core developers
  // Distributed under the MIT software license, see the accompanying
  // file COPYING or http://www.opensource.org/licenses/mit-license.php.
  
  // Based on https://github.com/mjosaarinen/tiny_sha3/blob/master/sha3.c
  // by Markku-Juhani O. Saarinen <mjos@iki.fi>
  
  #include <crypto/sha3.h>
  #include <crypto/common.h>
  #include <span.h>
  
  #include <algorithm>
  #include <array> // For std::begin and std::end.
  
  #include <stdint.h>
  
  // Internal implementation code.
  namespace
  {
  uint64_t Rotl(uint64_t x, int n) { return (x << n) | (x >> (64 - n)); }
  } // namespace
  
  void KeccakF(uint64_t (&st)[25])
  {
      static constexpr uint64_t RNDC[24] = {
          0x0000000000000001, 0x0000000000008082, 0x800000000000808a, 0x8000000080008000,
          0x000000000000808b, 0x0000000080000001, 0x8000000080008081, 0x8000000000008009,
          0x000000000000008a, 0x0000000000000088, 0x0000000080008009, 0x000000008000000a,
          0x000000008000808b, 0x800000000000008b, 0x8000000000008089, 0x8000000000008003,
          0x8000000000008002, 0x8000000000000080, 0x000000000000800a, 0x800000008000000a,
          0x8000000080008081, 0x8000000000008080, 0x0000000080000001, 0x8000000080008008
      };
      static constexpr int ROUNDS = 24;
  
      for (int round = 0; round < ROUNDS; ++round) {
          uint64_t bc0, bc1, bc2, bc3, bc4, t;
  
          // Theta
          bc0 = st[0] ^ st[5] ^ st[10] ^ st[15] ^ st[20];
          bc1 = st[1] ^ st[6] ^ st[11] ^ st[16] ^ st[21];
          bc2 = st[2] ^ st[7] ^ st[12] ^ st[17] ^ st[22];
          bc3 = st[3] ^ st[8] ^ st[13] ^ st[18] ^ st[23];
          bc4 = st[4] ^ st[9] ^ st[14] ^ st[19] ^ st[24];
          t = bc4 ^ Rotl(bc1, 1); st[0] ^= t; st[5] ^= t; st[10] ^= t; st[15] ^= t; st[20] ^= t;
          t = bc0 ^ Rotl(bc2, 1); st[1] ^= t; st[6] ^= t; st[11] ^= t; st[16] ^= t; st[21] ^= t;
          t = bc1 ^ Rotl(bc3, 1); st[2] ^= t; st[7] ^= t; st[12] ^= t; st[17] ^= t; st[22] ^= t;
          t = bc2 ^ Rotl(bc4, 1); st[3] ^= t; st[8] ^= t; st[13] ^= t; st[18] ^= t; st[23] ^= t;
          t = bc3 ^ Rotl(bc0, 1); st[4] ^= t; st[9] ^= t; st[14] ^= t; st[19] ^= t; st[24] ^= t;
  
          // Rho Pi
          t = st[1];
          bc0 = st[10]; st[10] = Rotl(t, 1); t = bc0;
          bc0 = st[7]; st[7] = Rotl(t, 3); t = bc0;
          bc0 = st[11]; st[11] = Rotl(t, 6); t = bc0;
          bc0 = st[17]; st[17] = Rotl(t, 10); t = bc0;
          bc0 = st[18]; st[18] = Rotl(t, 15); t = bc0;
          bc0 = st[3]; st[3] = Rotl(t, 21); t = bc0;
          bc0 = st[5]; st[5] = Rotl(t, 28); t = bc0;
          bc0 = st[16]; st[16] = Rotl(t, 36); t = bc0;
          bc0 = st[8]; st[8] = Rotl(t, 45); t = bc0;
          bc0 = st[21]; st[21] = Rotl(t, 55); t = bc0;
          bc0 = st[24]; st[24] = Rotl(t, 2); t = bc0;
          bc0 = st[4]; st[4] = Rotl(t, 14); t = bc0;
          bc0 = st[15]; st[15] = Rotl(t, 27); t = bc0;
          bc0 = st[23]; st[23] = Rotl(t, 41); t = bc0;
          bc0 = st[19]; st[19] = Rotl(t, 56); t = bc0;
          bc0 = st[13]; st[13] = Rotl(t, 8); t = bc0;
          bc0 = st[12]; st[12] = Rotl(t, 25); t = bc0;
          bc0 = st[2]; st[2] = Rotl(t, 43); t = bc0;
          bc0 = st[20]; st[20] = Rotl(t, 62); t = bc0;
          bc0 = st[14]; st[14] = Rotl(t, 18); t = bc0;
          bc0 = st[22]; st[22] = Rotl(t, 39); t = bc0;
          bc0 = st[9]; st[9] = Rotl(t, 61); t = bc0;
          bc0 = st[6]; st[6] = Rotl(t, 20); t = bc0;
          st[1] = Rotl(t, 44);
  
          // Chi Iota
          bc0 = st[0]; bc1 = st[1]; bc2 = st[2]; bc3 = st[3]; bc4 = st[4];
          st[0] = bc0 ^ (~bc1 & bc2) ^ RNDC[round];
          st[1] = bc1 ^ (~bc2 & bc3);
          st[2] = bc2 ^ (~bc3 & bc4);
          st[3] = bc3 ^ (~bc4 & bc0);
          st[4] = bc4 ^ (~bc0 & bc1);
          bc0 = st[5]; bc1 = st[6]; bc2 = st[7]; bc3 = st[8]; bc4 = st[9];
          st[5] = bc0 ^ (~bc1 & bc2);
          st[6] = bc1 ^ (~bc2 & bc3);
          st[7] = bc2 ^ (~bc3 & bc4);
          st[8] = bc3 ^ (~bc4 & bc0);
          st[9] = bc4 ^ (~bc0 & bc1);
          bc0 = st[10]; bc1 = st[11]; bc2 = st[12]; bc3 = st[13]; bc4 = st[14];
          st[10] = bc0 ^ (~bc1 & bc2);
          st[11] = bc1 ^ (~bc2 & bc3);
          st[12] = bc2 ^ (~bc3 & bc4);
          st[13] = bc3 ^ (~bc4 & bc0);
          st[14] = bc4 ^ (~bc0 & bc1);
          bc0 = st[15]; bc1 = st[16]; bc2 = st[17]; bc3 = st[18]; bc4 = st[19];
          st[15] = bc0 ^ (~bc1 & bc2);
          st[16] = bc1 ^ (~bc2 & bc3);
          st[17] = bc2 ^ (~bc3 & bc4);
          st[18] = bc3 ^ (~bc4 & bc0);
          st[19] = bc4 ^ (~bc0 & bc1);
          bc0 = st[20]; bc1 = st[21]; bc2 = st[22]; bc3 = st[23]; bc4 = st[24];
          st[20] = bc0 ^ (~bc1 & bc2);
          st[21] = bc1 ^ (~bc2 & bc3);
          st[22] = bc2 ^ (~bc3 & bc4);
          st[23] = bc3 ^ (~bc4 & bc0);
          st[24] = bc4 ^ (~bc0 & bc1);
      }
  }
  
  SHA3_256& SHA3_256::Write(Span<const unsigned char> data)
  {
      if (m_bufsize && m_bufsize + data.size() >= sizeof(m_buffer)) {
          // Fill the buffer and process it.
          std::copy(data.begin(), data.begin() + sizeof(m_buffer) - m_bufsize, m_buffer + m_bufsize);
          data = data.subspan(sizeof(m_buffer) - m_bufsize);
          m_state[m_pos++] ^= ReadLE64(m_buffer);
          m_bufsize = 0;
          if (m_pos == RATE_BUFFERS) {
              KeccakF(m_state);
              m_pos = 0;
          }
      }
      while (data.size() >= sizeof(m_buffer)) {
          // Process chunks directly from the buffer.
          m_state[m_pos++] ^= ReadLE64(data.data());
          data = data.subspan(8);
          if (m_pos == RATE_BUFFERS) {
              KeccakF(m_state);
              m_pos = 0;
          }
      }
      if (data.size()) {
          // Keep the remainder in the buffer.
          std::copy(data.begin(), data.end(), m_buffer + m_bufsize);
          m_bufsize += data.size();
      }
      return *this;
  }
  
  SHA3_256& SHA3_256::Finalize(Span<unsigned char> output)
  {
      assert(output.size() == OUTPUT_SIZE);
      std::fill(m_buffer + m_bufsize, m_buffer + sizeof(m_buffer), 0);
      m_buffer[m_bufsize] ^= 0x06;
      m_state[m_pos] ^= ReadLE64(m_buffer);
      m_state[RATE_BUFFERS - 1] ^= 0x8000000000000000;
      KeccakF(m_state);
      for (unsigned i = 0; i < 4; ++i) {
          WriteLE64(output.data() + 8 * i, m_state[i]);
      }
      return *this;
  }
  
  SHA3_256& SHA3_256::Reset()
  {
      m_bufsize = 0;
      m_pos = 0;
      std::fill(std::begin(m_state), std::end(m_state), 0);
      return *this;
  }
  