text: // Copyright (c) 2012-2017, The CryptoNote developers, The Marcoin developers
  //
  // This file is part of Marcoin.
  //
  // Bytecoin is free software: you can redistribute it and/or modify
  // it under the terms of the GNU Lesser General Public License as published by
  // the Free Software Foundation, either version 3 of the License, or
  // (at your option) any later version.
  //
  // Bytecoin is distributed in the hope that it will be useful,
  // but WITHOUT ANY WARRANTY; without even the implied warranty of
  // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  // GNU Lesser General Public License for more details.
  //
  // You should have received a copy of the GNU Lesser General Public License
  // along with Bytecoin.  If not, see <http://www.gnu.org/licenses/>.
  
  #include <alloca.h>
  #include <assert.h>
  #include <stddef.h>
  #include <string.h>
  
  #include "hash-ops.h"
  
  void tree_hash(const char (*hashes)[HASH_SIZE], size_t count, char *root_hash) {
    assert(count > 0);
    if (count == 1) {
      memcpy(root_hash, hashes, HASH_SIZE);
    } else if (count == 2) {
      cn_fast_hash(hashes, 2 * HASH_SIZE, root_hash);
    } else {
      size_t i, j;
      size_t cnt = count - 1;
      char (*ints)[HASH_SIZE];
      for (i = 1; i < 8 * sizeof(size_t); i <<= 1) {
        cnt |= cnt >> i;
      }
      cnt &= ~(cnt >> 1);
      ints = alloca(cnt * HASH_SIZE);
      memcpy(ints, hashes, (2 * cnt - count) * HASH_SIZE);
      for (i = 2 * cnt - count, j = 2 * cnt - count; j < cnt; i += 2, ++j) {
        cn_fast_hash(hashes[i], 2 * HASH_SIZE, ints[j]);
      }
      assert(i == count);
      while (cnt > 2) {
        cnt >>= 1;
        for (i = 0, j = 0; j < cnt; i += 2, ++j) {
          cn_fast_hash(ints[i], 2 * HASH_SIZE, ints[j]);
        }
      }
      cn_fast_hash(ints[0], 2 * HASH_SIZE, root_hash);
    }
  }
  
  size_t tree_depth(size_t count) {
    size_t i;
    size_t depth = 0;
    assert(count > 0);
    for (i = sizeof(size_t) << 2; i > 0; i >>= 1) {
      if (count >> i > 0) {
        count >>= i;
        depth += i;
      }
    }
    return depth;
  }
  
  void tree_branch(const char (*hashes)[HASH_SIZE], size_t count, char (*branch)[HASH_SIZE]) {
    size_t i, j;
    size_t cnt = 1;
    size_t depth = 0;
    char (*ints)[HASH_SIZE];
    assert(count > 0);
    for (i = sizeof(size_t) << 2; i > 0; i >>= 1) {
      if (cnt << i <= count) {
        cnt <<= i;
        depth += i;
      }
    }
    assert(cnt == 1ULL << depth);
    assert(depth == tree_depth(count));
    ints = alloca((cnt - 1) * HASH_SIZE);
    memcpy(ints, hashes + 1, (2 * cnt - count - 1) * HASH_SIZE);
    for (i = 2 * cnt - count, j = 2 * cnt - count - 1; j < cnt - 1; i += 2, ++j) {
      cn_fast_hash(hashes[i], 2 * HASH_SIZE, ints[j]);
    }
    assert(i == count);
    while (depth > 0) {
      assert(cnt == 1ULL << depth);
      cnt >>= 1;
      --depth;
      memcpy(branch[depth], ints[0], HASH_SIZE);
      for (i = 1, j = 0; j < cnt - 1; i += 2, ++j) {
        cn_fast_hash(ints[i], 2 * HASH_SIZE, ints[j]);
      }
    }
  }
  
  void tree_hash_from_branch(const char (*branch)[HASH_SIZE], size_t depth, const char *leaf, const void *path, char *root_hash) {
    if (depth == 0) {
      memcpy(root_hash, leaf, HASH_SIZE);
    } else {
      char buffer[2][HASH_SIZE];
      int from_leaf = 1;
      char *leaf_path, *branch_path;
      while (depth > 0) {
        --depth;
        if (path && (((const char *) path)[depth >> 3] & (1 << (depth & 7))) != 0) {
          leaf_path = buffer[1];
          branch_path = buffer[0];
        } else {
          leaf_path = buffer[0];
          branch_path = buffer[1];
        }
        if (from_leaf) {
          memcpy(leaf_path, leaf, HASH_SIZE);
          from_leaf = 0;
        } else {
          cn_fast_hash(buffer, 2 * HASH_SIZE, leaf_path);
        }
        memcpy(branch_path, branch[depth], HASH_SIZE);
      }
      cn_fast_hash(buffer, 2 * HASH_SIZE, root_hash);
    }
  }
  